Abu Dhabi, United Arab Emirates. STANDARD CONSTRUCTION SPECIFICATIONS (PART 2 - ROAD STRUCTURES, 2020)

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-18

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

and the existing water shall result in a plastic material. This is necessary for the EPB to control the
face in front of the bulkhead and to bring the material from its pressurised state at the face down to
ambient by means of the EPB screw conveyor.

For these reasons, the Contractor shall not build a closed-face rock machine but to equip an EPB
with rock cutters for driving short stretches in rock within a longer soft-ground tunnel. An exception
to this general statement shall be a rock tunnel in weak or soft rock, such as chalk, marl, shale, or
sandstone of quite low strength that essentially behaves as high-strength soft ground.

34.3.4.7

Other Measures of Groundwater Control

Groundwater control methods presented above shall account for more than 95 percent of the cases
where such control will be required in the rock tunnel. In case, for the tunnels or shafts where
something else is required, the Contractor may rely on experience or ingenuity to come up with the
solution. A few suggestions are presented here, but the Contractor may have to develop inventive
solutions on a case-by-case basis.

Compressed Air:

Where the tunnel, or shaft, can be stabilised by relatively low pressures measuring

0.07 MPa, or less, the Contractor may use compressed air; however, it requires compressor plants,
locks, special medical emergency preparation, and decompression times.

Panning may be attractive in some cases where the water inflow is not too excessive and is
concentrated at specific points or seams. In this case, pans are placed over the leaks and shotcreted
into place. Water is carried in chases or tubes to the invert and dumped into the tunnel drainage
system.

Drainage fabric could be used in rock tunnels. These geotechnical fabrics shall be installed over the
whole tunnel circumference, in strips on a set pattern, or where the leaks are occurring. Fastened to
the surface of the rock with the waterproof membrane portion facing into the tunnel, this fabric shall
then be sandwiched into place by the cast-in-place concrete lining. Fibrous portions of the fabric
shall provide a drainage pathway around and down the tunnel walls and into a collection system at
the tunnel invert.

34.3.5

Waterproofing of Tunnels in Rock

Unless otherwise specified, tunnels in rock shall be waterproofed by a sandwich consisting of:

a. A geotechnical drainage fabric that is put in place directly against the rock either continuously

or in strips. This may be held in place by pins or nails driven or shot into the rock.

b. A continuous waterproof membrane of high density polyethylene (HDPE) or polyvinylchloride

(PVC) or other similar material, as indicated in the Contract plans, specified in the particular
specifications, and approved by the Engineer. To be continuous the membrane has to be cut
and fit to all strange shapes and corners encountered and welded together (by heat) to make
a continuous waterproofing membrane within the tunnel. The Contractor shall successfully
install the waterproofing system and provide the proper workmanship in:

•

Avoiding puncturing, tearing and the like of the membrane.

•

Correctly making and testing all joints.

•

Connecting the waterproof membrane to the wall without introducing leaks.

c. A cast in place lining of concrete placed to hold the sandwich together and to provide the

desired inner surface of the tunnel. The Contractor shall ensure that the concrete is placed
without damaging the membrane(s).

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-19

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

34.4

Soft-Ground Tunnelling

34.4.1

Introduction

This work shall construct tunnelling, mostly shield tunnelling, in soft ground

— including cohesive

soils, cohesionless soils, and silty sands.

34.4.2

Tunnelling-Induced Settlement

34.4.2.1

General

Ground settlement is of greater concern for soft-ground tunnels than for rock for the following two
reasons:

•

Settlements are nearly always greater for soft-ground tunnels.

•

Typically more facilities that might be negatively impacted by settlements exist near soft-

ground tunnels than near rock tunnels.

To minimise settlements and their impact on other facilities, the Contractor shall be fully equipped.

34.4.2.2

Sources of Settlement

Although there are a large number of sources or causes of settlement, they can be conveniently
lumped into the following two broad categories:

•

those caused by groundwater depression; and,

•

those caused by lost ground.

a. Groundwater Depression

Groundwater depression may be caused by intentional lowering of the water during construction or
by the tunnel or other construction acting as a drain. When any of these occurs, the effective stress
in the ground increases. For tunnels in granular soil, the settlement due to this increase in effective
stress is usually reflected as an elastic phenomenon requiring knowledge of the low-stress modulus
of the ground and calculation of the change in effective stress. Unless the soil contains silt or very-
fine sand, this elastic settlement will typically represent the majority of the total but its absolute value
will also be relatively small.

With fine-grained soils, the conditions are reversed. In most instances, the settlement is mostly due
to consolidation brought on by the changes in effective stress. In some instances, primarily if lenses
of sands are contained in the soil, there may also be a relatively small contribution by elastic
compression. In comparison to the settlement of granular soils, consolidation can lead to
considerable settlement when the consolidating soils are thick and the change in effective stress is
significant.

b. Lost Ground

Lost ground has a number of root causes and is usually responsible for the settlements. By definition,
lost ground refers to the act of taking, or losing, more ground into the tunnelling operation than is
represented by the volume of the tunnel. Thus it is highly reflective of construction means and
methods. Modern machines shall be used by the Contractor in controlling lost ground and employ
high-quality workmanship.

For the purposes of this section, the causes of lost ground shall be lumped into the following three
groups:

•

Face losses

results from movement in front of and into the shield. This includes running,

flowing, caving, and squeezing behaviour of the ground itself or simply mining more ground
than displaced by the tunnelling machine.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-20

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

•

Shield losses

occur between the cutting edge and the tail of the shield. All shields employ

some degree of overcut so that they can be manoeuvred. Additionally, any time a shield is
off alignment, the shield yaws, pitches, or plows, when brought back to alignment. Mother
Nature abhors a vacuum and the surrounding soils begin to fill these planned or produced
voids the instant they are produced. The Contractor shall note that a 25-mm overcut plus a
3-mm hard facing on a 6-m shield produces lost ground of nearly 2 percent, if not properly
filled.

•

Tail losses

are similar to shield losses in that they are caused by the space being vacated

by the tail itself

— as well as the extra space that must be provided between the tail and the

support elements so these elements can be erected and so that they  do not become iron
bound and seize the tail shield. However, like the shield losses, these tail voids will rapidly fill
with  soil  if  they  are  not  first  eliminated  by  grouting  or  expansion  of  the  tunnel  support
elements.

34.4.2.3

Settlement Calculations

In tunnelling, the Contractor shall rely heavily on its experience with some assistance from analysis.
Thus, there are two related methods to attack the problem: experience and empirical data.

Experience can be used where a history of tunnelling and of taking of measurements exists. It shall
be anticipated that an experienced Contractor shall achieve between 0.5 percent and 1 percent
ground loss (refer to Table 34-2) while an inexperienced Contractor shall attain 1 percent to 2 percent
loss.

Table 34-2: Relationship between volume loss, construction practice,

and ground conditions

Case

VL (%)

Good practice in firm ground; tight control of face pressure within closed-face
machine in slowly ravelling or squeezing ground

0.5

Usual practice with closed-face machine in slowly ravelling or squeezing ground

Poor practice with closed-face machine in ravelling ground

Poor practice with closed-face machine in poor, or fast ravelling, ground

Poor practice with little face control in running ground

4, or more

When there is no record to rely upon, the design shall be based strictly on empirical data and an
engineering assessment of what the Contractor could be expected to achieve with no track record
to rely upon. In that case, the above evaluations might be bumped up one-half of a percentage point
each as an insurance measure.

Pressurised-face TBMs, such as EPB and SFM, shall be employed by the Contractor to minimise
the magnitude of ground losses. These machines control face stability by applying active pressure
to the tunnel face, minimizing the amount of overcut, and using automatic tail void grouting to reduce
shield losses. Typically, ground loss during soft-ground tunnel excavation using this technology limits
ground loss to 1 percent, or less

— assuming excellent tunnelling practice that includes adequate

pressure applied to the face and effective and timely tail void grouting.

Ground settlement can be predicted by numerical methods, which are extremely useful when the
tunnel geometry is not a circular or horse-shoe shape because the analytical, or empirical, method
was not directly applicable.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-21

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

34.4.3

Impact on and Protection of Surface Facilities

34.4.3.1

Evaluation of Structure Tolerance to Settlement

Evaluation of structural tolerance to settlement requires definition of the possible damage that a
structure might experience. Surface structures damaged due to tunnelling-induced settlement shall
be defined by the following:

Architectural Damage:

Damage affecting the appearance but not the function of

structures, usually related to cracks or separations in panel walls, floors, and finishes.
Cracks in plaster walls greater than 0.4 mm wide and cracks in masonry or rough
concrete walls greater than 0.8 mm wide are representative of a threshold where damage
is noticed and reported by building occupants.

Functional Damage:

Damage affecting the use of the structure, or safety to its occupants,

usually related to jammed doors and windows, cracking and falling plaster, tilting of walls
and floors, and other damage that requires nonstructural repair to return the building to
its full-service capacity.

Structural Damage:

Damage affecting the stability of the structure, usually related to

cracks or distortions in primary support elements

— such as beams, columns, and load-

bearing walls.

Table 32-2 presents the correlation of angular distortion (the relative settlement between columns or
measurement points) and building damage.

As an alternative initial screening method, Table 34-3 presents a damage risk assessment chart,
based on maximum building slope and settlement.

Table 34-3: Limiting angular distortion

Category of Potential Damage

Angular Distortion

Danger to machinery sensitive to settlement

1/750

Danger to frames with diagonals

1/600

Safe limit for no cracking of building

1/500

First cracking of panel walls

1/300

Difficulties with overhead cranes

1/300

Tilting of high-rigid building becomes visible

1/250

Considerable cracking of panel and brick walls

1/150

Danger of structural damage to general building

1/150

Safe limit for flexible brick walls*

1/150

*A safe limit includes a factor of safety

Table 34-4: Damage risk assessment chart

Risk

Category

Maximum

slope of
building

Maximum

settlement of

building (mm)

Description of risk

Less than 1/500

Less than 10

Negligible; superficial damage unlikely.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-22

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

Table 34-4: Damage risk assessment chart

Risk

Category

Maximum

slope of
building

Maximum

settlement of

building (mm)

Description of risk

1/500

– 1/200

– 50

Slight; possible superficial damage that is
unlikely to have structural significance

1/200

– 1/50

– 75

Moderate; expected superficial damage and
possible structural damage to buildings, possible
damage to relatively rigid pipelines.

Greater than

1/50

Greater than 75

High; expected structural damage to buildings.
Expected damage to rigid pipelines, possible
damage to other pipelines

34.4.3.2

Mitigating Settlement

Where the settlement is, or shall be, caused by groundwater lowering, the Contractor shall reduce
or eliminate the conditions causing or allowing dewatering. This could include the following, for
example:

a. Reduce drawdown at critical structures by re-injecting water or using impervious cut off walls.

b. Using closed- and pressurised-face tunnelling machines so that drawdown cannot occur.

Pressure at the face shall be equal to the groundwater head.

c. Grouting the ground around the tunnel to eliminate water inflow into the tunnel.

Where the settlement is or could be caused by lost ground in the tunnelling operation, the Contractor
shall mitigate that settlement with proper construction means and methods. For example, the
Contractor shall consider the following:

•

Requiring a closed-face, pressurised TBM, such as an EPB or SFM, and keep the pressure

at least equal to

— if not greater than — the combined soil and groundwater pressure in the

ground at tunnel level.

•

Immediately and completely grout the annular space between the tunnel lining and the

ground at the tail of the machine. Use automated grouting systems that will not permit the
machine to advance without this void being simultaneously grouted.

•

Control the operation, or steering, of the machine so that it is not forced to pitch or yaw to

make excessive alignment corrections. Each 1 percent of correction translates to a potential
1.5 percent of ground loss.

•

Use compaction or compensation grouting to make up for ground loss before it migrates to

the building.

•

Treat areas of loose soils by consolidation or jet grouting before tunnelling into them.

34.4.3.3

Structure Protection

When protecting structures, first and foremost are the tunnelling procedures of maintaining face
pressure, or control, and immediately grouting to fill the annular

— or any other — void.

The next step is ground improvement either by consolidation or jet grouting, and closely related
compensation or compaction grouting.

As a last resort, the Contractor shall apply underpinning, when all else appears to be unsuccessful
and or unworkable. Typical steps of underpinning method are summarised as follows:

•

Break out and hand excavate down to, or nearly to, the potentially impacted foundation.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-23

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

•

Install piles or other founding elements to a bearing below or outside the impacted foundation

and the tunnel.

•

Install a needle beam or similar method to transfer the impacted foundation load to the new

elements.

•

Preload the new elements, such as unloading the impacted foundation onto those new

elements.

•

Cut or release any load to the impacted foundation. At this point, all loads are transferred

through the new elements to a bearing location/condition that is completely independent of
the tunnelling operation and the tunnel.

•

As required or necessary remove or leave in place the original foundation.

34.4.4

Soil Stabilization and Improvement

34.4.4.1

Introduction

This work shall include soil stabilization and improvement works.

34.4.4.2

Typical Applications

The Contractor shall take the decision to use soil stabilization or improvement based on each
individual case. This decision may be easy with there being no other way to construct the tunnel. Or
the decision may come down to a trade-off among treating the ground, using high-tech machines, or
a combination of the two. Table 34-5 summarises the challenging ground sites and corresponding
treatment methods.

Table 34-5: Ground treatment methods

Challenging Ground Conditions

Treatment Methods

Weak Soils

Vibro Compaction
Dynamic Compaction
Compaction Grouting
Permeation Grouting
Jet Grouting

Groundwater

Dewatering
Freezing
Grouting

Unstable Face

Soil Nails
Spiling
Soil Dowelling
Micro-Piles

Soil Movement

Compensation Grouting
Compaction Grouting

The Contractor shall note that the boundaries between both ground conditions and treatment
methods are not fixed. Additionally, the use of vibro compaction techniques or dynamic compaction
is typically applicable at or near the tunnel portals, as these techniques are applied to the ground
surface and are not effective beyond an approximate 30-m-depth for vibro compaction and 10-m-
depth for dynamic compaction. Both are generally effective only in granular soils.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-24

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

34.4.4.3

Reinforcement Methods

a. Soil Nails

Soil nails may be used to stabilise a tunnel face in soil during construction. Steel or fibreglass rods
or nails shall be installed in the face and the resulting reinforced blocks shall be analyzed for stability
— much as for usual slope stability analyses. Several methods, such as Davis, Modified Davis,
German, French, Kinematrical, Golder, and Caltrans, are used for these analyses. However, it must
be recognised that application of any method must be tempered with appropriate judgment,
measurements, and case history experience.

b. Soil Dowelling

Soil dowelling entails the installation of reinforcement members that are larger than nailing. These
dowels act in tension, like soil nails, but are large enough in the cross section that they also develop
some shearing resistance where they pass through the sliding surfaces.

34.4.4.4

Micropiles

As they are applied to tunnelling, micropiles are essentially the same as soil dowels. These shall be
drilled piles measuring 50 mm to 150 mm in diameter that contain a large, reinforcing bar centred in
the hole and the hole backfilled with concrete. As opposed to pin piles that are typically installed at
the surface, and that act in compression, the pin piles placed in tunnels typically act in tension and
shear across the sliding surfaces.

Soil nails, soil dowels, and pin piles shall be installed at the face of the tunnel to stabilise that face
for construction. Thus, they are continually being installed and mined out of the face. For ease in this
mining operation, fibreglass bars

— or rods — shall be used in these applications because they are

much easier to mine out and cut. In contrast, spiling tends to look out around the perimeter of the
tunnel, thus steel is more likely to be used for spiling bars or plates.

For more details, the Contractor shall comply with requirements of

the “Micropile Design and

Construction Reference Manual

,” FHWA, 2005f.

34.4.4.5

Grouting Methods

All grouting involves the drilling of holes into the ground, the insertion of grout pipes in the holes, and
the injection of pressurised grout into the ground from those pipes. Details of the operations,
however, are distinctly different.

a. Permeation Grouting

Permeation grouting involves the filling of pore spaces between soil grains, and displacing water.
Grout may be one of a number of chemicals, but is usually sodium silicate or polyurethane; or neat
cement using regular, micro-, or ultra- fine cement, along with chemicals and other additives. Once
injected into the pore spaces, the grout sets and converts the soil into a stable, weak sandstone
material. Permeation grouting usually involves grout holes with 0.9-m to 1.2-m centres and enough
secondary holes at split spacing to verify that all the ground is grouted. If necessary to get full
coverage, all of the split-spacing holes may have to be grouted and verification performed by the
tertiary holes.

b. Compaction Grouting

Compaction grouting uses a stiffer grout than permeation grouting. In compaction grouting, the goal
is to form a series of grout bulbs or zones 1.2 m to 1.8 m above and around the tunnel crown. By
pumping the stiff grout under pressure, these bulbs compress, or densify, the ground above and
between the tunnel and overlying facilities.

Pipes for compaction grouting are prepositioned and drilled into place and all the grouting pumps,
hoses, header pipes, and instrumentation are in place before the tunnel drive begins. Instrumentation
is read as the tunnel approaches and passes a facility and the grouting operation is adjusted in real

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-25

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

time in response to the movement readings. Additionally, it is possible to either preheave the ground
or to jack it back up, at least partially, by pumping more grout at higher pressures.

c. Compensation Grouting

Compensation grouting is, in some ways, similar to compaction grouting. The goal is to monitor
ground movements, primarily between the tunnel and any overlying facility. When it is apparent that
ground is being lost in the tunnelling operation, a grout, typically slightly more liquid than the
compaction grout mix, is injected to replace

— or compensate for — the lost ground. As indicated,

the differences between these two schemes are relatively minor, as compaction grouting seeks to
recompact the ground by forming grout bulbs and compensation grouting seeks to refill voids created
by the tunnelling operations.

d. Jet Grouting

Jet grouting uses high-pressure jets to break up the soils and replace them with a mixture of
excavated soils and cement. This is typically referred to as soilcrete. There are a number of variations
of jet grouting, depending on the details of the application and on the experience and expertise of
the Contractor.

Design of a jet-grouted column is influenced by a number of interdependent variables related to in
situ soil conditions, materials used, and operating parameters. Table 34-6 presents a summary of
the principal variables of the jet grouting system and their potential impact on the three basic design
aspects of the jet-grouted wall: column diameter, strength, and permeability. Table 34-6 also gives
typical ranges of operating parameters and results achieved by the three basic injection systems of
jet grouting. It shall be noted that the grout pressures indicated in this table are based on certain
equipment and can vary. This table can be used in feasibility studies and preliminary design of jet-
grouted wall systems. Actual operating parameters used in production are usually determined from
initial field trials performed at the beginning of construction.

Jet grouting shall be used as a ground control measure in conjunction with tunnelling in soft ground
using SEM.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-26

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

Table 34-6: Summary of jet grouting system variables

and their impact on basic design elements

Principal
Variables

General Effect of the Variable on Basic Design Elements (Strength,
Permeability, and Column Diameter)

(a) Jet-Grouted Soil Strength

Degree of
mixing of soil
and grout

Strength is higher and less variable for a higher degree of mixing.

Soil type and
gradation

Sands and gravels tend to produce stronger material while clays and silts tend
to produce weaker material.

Cement factor

Strength increases with an increase in cement factor, such as weight of cement
per volume of jet-grouted mass.

Water to cement
ratio of grouted
mass

Strength of the jet-grouted soil mass decreases with increase to in situ water to
cement ratio.

Jet grouting
system

The strength of the double fluid system may be reduced due to air entrapment in
the soil-grout mix.

Age of grouted
mass

As the jet-grouted soil mass cures, the strength increases but usually at a
slower rate than that of concrete.

(b) Wall Permeability

Wall continuity

Overall permeability of a jet-grouted wall is almost entirely contingent on the
continuity of the wall between adjacent columns or panels. Plumb, overlapping
multiple rows of columns shall produce lower overall permeability. In cases of
obstructions, such as boulders and utilities, if complete encapsulation is not
achieved then overall permeability may be increased, due to possible leakage
along the obstruction-grout interfaces.

Grout
composition

Assuming complete wall continuity and complete replacement of in situ soil, the
lowest permeability that can be obtained is that of the grout, typically measuring
10-6 cm/sec to 10-7 cm/sec. Lower permeabilities may be possible if bentonite,
or a similar waterproofing, additive is used.

Soil composition If complete replacement is obtained, as may be possible with a triple fluid

system, then soil composition does not matter. Otherwise, if uniform mixing is
achieved than finer-grained soils shall produce lower permeabilities, as
compared to granular soils.

(c) Column Diameter

Jet grouting
system

The diameter of the completed column increases in size as the number of fluids
is increased from the single to the triple fluid systems.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-27

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

Soil density and
gradation

As density increases, column diameter reduces. For granular soils, the diameter
increases with reducing uniformity coefficient (D60/D10).

Degree of
mixing of soil
and grout

Larger and more uniform diameters are possible with a higher degree of mixing.

34.4.4.6

Ground Freezing

Ground freezing provides means of obtaining access in unfavourable ground conditions, of providing
emergency support in unstable ground below the water table, and of maintaining stability of working
faces below the water table.

Ground freezing involves the extraction of heat from the ground until the groundwater is frozen, thus
converting the groundwater into a cementing agent and the ground into frozen sandstone. Heat is
extracted by circulating a cooling liquid, usually brine, in an array of pipes. Each pipe is actually two
nested pipes, with the liquid flowing down the centre pipe and back out through the annulus between
the pipes. When the pipes are close enough and the time long enough, the cylinders of frozen soil
formed at each pipe eventually coalesce into one solid frozen mass. This mass may be a ring or
donut as needed to support a shaft or a solid block of whatever shape necessary to stabilise the
working face or heading.

In early design of ground freezing, the Contractor is recommended to take the following two steps:

•

A professional engineer shall advise on the design and construction of the Project.

•

Laboratory tests shall be carried out using soil samples from the actual site. Only in this

manner can meaningful properties of frozen soil be obtained for the site involved.

However, a few general guidelines can be stated as follows:

•

Pipes are normally spaced 0.9 m to 1.2 m apart.

•

Select a spacing-to-diameter ratio <13 for pipes measuring 120 mm or less in diameter.

•

Use a brine temperature <25 degrees Celsius.

•

Provide 0.013 tons to 0.025 tons of refrigeration per 300 mm of freeze pipe.

•

Determine typical frozen ground properties by laboratory testing.

Groundwater flow across the site requires special considerations, such as closer pipe spacing and
multiple rows of pipes. Groundwater flow velocities of approximately >2 m/day may impede or
prevent freezing. A number of special challenges associated with ground freezing shall be
considered in both the design and construction stage. Those are creep of frozen ground, sensitivity
of frozen ground properties to loading condition, and ground heave or settlement.

34.5

Steel and Concrete Tunnel Liners

34.5.1

Scope

These Specifications are intended to cover the installation of tunnel liner plates in tunnels
constructed by conventional tunnel methods.

Tunnels excavated by full face, heading and bench, or multiple drift procedures are considered
conventional methods.

Liner plates used with any construction procedure using a full or partial shield; a tunnelling machine;
or other piece of equipment that will exert a force on the liner plates for the purpose of propelling,
steering, or stabilizing the equipment are considered special cases and are not covered by these
Specifications.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-28

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

34.5.2

Description

This work shall furnish cold-formed steel tunnel liner plates or precast concrete plates, conforming
to these Specifications and of the sizes and dimensions required in the Contract documents, and
installing such plates at the locations specified in the Contract documents or by the Engineer and in
conformity with the lines and grades established or by the Engineer. Completed liner shall consist of
a series of liner plates assembled with staggered longitudinal joints.

Steel tunnel liner plates shall be of a type that is commercially available. Precast concrete tunnel
liner plates shall be such that their size and shape suits the method and equipment being used to
install them.

34.5.3

Materials and Fabrication

34.5.3.1

General

Steel liner plates herein described must meet the sectional properties of thickness, area, and
moment of inertia shown in the Contract documents. Liner plates shall be fabricated to fit the cross-
section of the tunnel. If not shown in the Contract documents, steel liner plate requirements and
properties shall be as specified in the AASHTO LRFD Bridge Design Specifications, Section 12.13.3,
and Road Structures Design Manual (ADQCC TR-516), as applicable.

All steel plates shall be connected by bolts on both longitudinal and circumferential seams or joints
and shall be so fabricated as to permit complete erection from the inside of the tunnel. Bolt sizes and
properties shall be in accordance with the Manufacturer's standard, but not less than those specified
in the AASHTO LRFD Bridge Design Specifications, Section 12.13.3.1.

Grout holes measuring 50 mm or larger in diameter shall be provided, as shown in the Contract
documents to permit grouting as the erection of tunnel liner plates progresses.

Precast concrete tunnel liner plates shall conform to the details shown in the Contract documents
and  the  requirements  of  Section  21.13  of  Chapter  21,  Concrete  Structures,  of  these  standard
specifications. If such details are not provided, and the Contract documents allow the Contractor to
propose  the  use  of  concrete  liner  plates,  the  Contractor  shall  submit  working  drawings  to  the
Engineer  for  approval.  Such  drawings  shall  describe  materials  to  be  used,  plate  dimensions,
reinforcement  details,  connecting  details,  and  erection  procedures.  Fabrication  of  the  Contractor-
proposed types of concrete tunnel liner plates shall not begin until the working drawings have been
approved.  Such  approval  shall  not relieve  the  Contractor  of  any responsibility  under  the  Contract
documents for the successful completion of the work.

34.5.3.2

Forming and Punching of Steel Liner Plates

All plates shall be formed to provide circumferential flanged joints. Longitudinal joints may be flanged
or  of  the  offset  lap  seam  type.  All  plates  shall  be  punched  for  bolting  on  longitudinal  and
circumferential seams or joints. Bolt spacing in circumferential flanges shall be in accordance with
the Manufacturer's standard spacing and shall be a multiple of the plate length so that plates having
the same curvature shall be interchangeable and will permit staggering of the longitudinal seams.
Bolt spacing at flanged longitudinal seams shall be in accordance with the Manufacturer's standard
spacing.  For  lapped  longitudinal  seams,  bolt  size  and  spacing  shall  be  in  accordance  with  the
Manufacturer's  standard  but  not  less  than  that  necessary  to  meet  the  longitudinal  seam  strength
requirements specified in the AASHTO LRFD Bridge Design Specifications, Section 12.13.3.1.

34.5.4

Installation

34.5.4.1

Steel Liner Plates

All steel liner plates for the full length of a specified tunnel shall be of one type only, either the flanged
or the lapped seam type of construction.

Liner plates shall be assembled in accordance with the Manufacturer's instructions.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-29

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

Coated-steel plates shall be handled in such a manner as to prevent bruising, scaling, or breaking
of the coating. Any plates that are damaged during handling or placing shall be replaced at the
Contractor's expense, except that small areas with minor damage may be repaired by the Contractor
as directed by the Engineer.

34.5.4.2

Precast Concrete Liner Plates

Installation of precast concrete tunnel liner plates shall not start prior to receipt of approval of working
drawings submitted, as required by Article 34.5.3.1, General. Installation shall conform to the
specified or approved erection procedures.

34.5.4.3

Grouting

When directed by the Engineer, voids occurring between the liner plate and the tunnel wall shall be
force-grouted. Grout shall be forced through the grouting holes in the plates with such pressure that
all voids will be completely filled. Full compensation for backpacking or grouting shall be considered
as included in the Contract price paid for tunnel and no separate payment will be made therefore.

34.6

Immersed Tunnels

34.6.1

Introduction

This work consists of constructing various types of immersed tunnels and their construction
techniques, including fabrication, transportation, placement, joining, backfilling, water tightness, and
the trench stability and foundation preparation requirements.

Immersed tunnels consist of large precast concrete or concrete-filled steel tunnel elements
fabricated in the dry and installed under water. Immersion tunnels shall be fabricated by the
Contractor in convenient lengths on shipways, in dry docks, or in improvised floodable basins, sealed
with bulkheads at each end, and then floated out. Tunnel elements can be towed successfully over
great distances. They may require outfitting at a pier close to their final destination. They shall be
then towed to their final location, immersed, lowered into a prepared trench, and joined to previously
placed tunnel elements. After additional foundation works have been completed, the trench around
the immersed tunnel shall be backfilled and the water bed reinstated. Unless specified in the Contract
documents, the top of the tunnel shall be at least 1.5 m below the original bottom to allow for sufficient
protective backfill. If the Contract documents and hydraulic regime allows, the tunnel may be placed
higher than the original water bed within an underwater protective embankment.

Immersed tunnel elements shall be floated to the site using their buoyant state; however, additional
external buoyancy tanks attached to the elements may be used, if necessary. The ends of the tunnel
elements shall be equipped with bulkheads, like dam plates, across the ends to keep the inside dry,
located to allow only approximately 2 m to 2.5 m between the bulkheads of adjacent elements at an
immersion joint; this space shall be emptied once an initial seal is obtained during the joining process.
Joints shall be equipped with gaskets to create the seal with the adjacent element. They shall also
be equipped with adjustment devices to allow placement of the elements on line and grade. Tunnel
elements shall be lowered into their location after adding either temporary water ballast or tremie
concrete.

34.6.1.1

Environmental Impact

Immersed tunnels have potential disadvantages in term of environmental disturbance to the water
body bed. They may have impact on fish habitats, ecology, current, and turbidity of the water.  All
precaution  measures  shall  be  taken  by  the  Contractor  to  minimise  the  impact  of  constructing
immerse  tunnels  on  the  surrounding  environment.  Furthermore,  impacts  on  navigation  in  all
navigable  waterways  shall  be  considered  and  often  extensive  permitting  shall  be  required.
Additionally,  many  of  the  water  bodies,  such  as  harbours,  or  causeways  have  contaminated
sediments  requiring  special  handling.  Use  of  immersed  tunnel  techniques  might  encounter  such
contaminated ground and shall require its regulated disposal.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-30

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

34.6.1.2

Types of Immersed Tunnel

There are two types of immersed tunnels that are known as steel and concrete tunnels. Steel tunnels
shall be structural steel in the form of stiffened plate, working compositely with the interior concrete
as the structural system. Concrete tunnels shall rely on steel reinforcing bars or prestressing cables.
Steel-immersed tunnel elements shall be fabricated in ship yards or dry docks similar to ships,
launched into water, and then outfitted with concrete while afloat. Concrete-immersed elements shall
be cast in dry docks, or specially built basins, then the basin shall be flooded and the elements are
floated out. Steel tunnels may have an initial draft of as little as about 2.5 m, whereas concrete
tunnels have a draft of almost the full depth. Tunnel cross sections may have flat or curved sides
that shall comply with the Contract plans.

Concrete tunnels shall be rectangular while steel tunnels shall be circular, curved with a flat bottom,
rectangular, or double-shell tunnel that is a circular shell within an octagonal shape. Most or all of
the concrete in steel tunnels shall be placed while the steel shell is afloat, in direct contrast to
concrete tunnels that are virtually complete before being floated out. The order in which concrete is
placed for a steel tunnel shall be tightly controlled to minimise deformations and the resulting
stresses. Steel immersed tunnels may be single shell, double shell, and sandwich.

34.6.1.3

Single-Shell Steel Tunnel

In this type, the external structural shell plate shall work compositely with the interior reinforced
concrete and no external concrete shall be provided. The shell plate shall require corrosion
protection in the form of cathodic protection.

The  initial  draft  of  a  single  shell  tunnel  shall  be  less  than  that  for  other  immersed  tunnel  types
because  of the  elimination  of the  outer  shell.  However,  leaks  in  the  steel  shell may  be  difficult  to
identify and seal; subdividing the surface into smaller panels by using ribs will improve the chances
of sealing a leak. Great care and considerable testing shall be required to ensure that the welds are
defect free. Permanent leakage risks can be higher in single-shell immersed tunnels than in other
types.  To  avoid  this,  the  external  structural  steel  shell  shall  require  a  positive  form  of  corrosion
protection.

34.6.1.4

Double Shell Tunnel

A double-shell tunnel element shall be comprised of an internal structural shell that acts compositely
with concrete placed within the steel shell. The top and invert concrete outside the structural shell
plate shall also be structural. A second steel shell shall be constructed outside the structural steel
shell to act as formwork for ballast concrete at the sides placed by tremie. In this configuration, the
interior structural shell plate shall work compositely with internal reinforced concrete while it is
protected by external concrete placed within non-structural steel form plates. The steel portion of the
double shell tunnel element shall be fabricated at a shipyard. Prior to launching, the invert concrete
may be placed to make the element more stable during towing and outfitting and to internally brace
the steel elements. Due to the double shell configuration, this element is stiffer than the single shell
section. However, due to the potential for rough conditions during towing and in particular during
launching if not constructed in a dry dock, internal bracing may be required until the tunnel element
is in its final position.

Multiple bores shall be created by linking sections with diaphragms. The diaphragms shall also serve
to stiffen the steel shell. Diaphragms shall be spaced along the length of the tunnel element.
Longitudinal stiffeners in the form of plates or T-sections shall be used in the longitudinal direction
of the element between diaphragms to stiffen the shell.

34.6.1.5

Sandwich Construction

This construction type shall consist of a structural concrete layer sandwiched between two steel
shells. Both the inner and outer shells shall be load carrying and both shall act compositely with the
inner concrete layer. The concrete shall be non-reinforced and formulated to be non-shrink and self-
consolidating. Inner surfaces of the steel shells shall be stiffened with plates and L-shaped ribs shall

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-31

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

also provide the connection required for composite action with the internal concrete. Internal
concrete, once cured, shall carry compression loads and shall also serve to stiffen the steel shells.
Steel shells shall carry the tension loads.

As with the other types, the steel shells shall be fabricated at a shipyard and launched and towed to
the tunnel site. Internal diaphragms between the two shells shall stiffen the section sufficiently to
resist the loads imposed during transport and outfitting. Once at the outfitting pier, the internal
concrete shall be placed and the element draft increases. Elements shall be towed to their locations
along the tunnel alignment and the final ballast and structural concrete shall be placed so that it can
be lowered into place.

Steel sandwich construction shall provide a double layer of protection against leaks; however, this
complex arrangement shall require the Contractor to carefully define the executed procedures for
fabrication and concreting. Distortion of the section during welding and poor quality welds can be
costly mistakes for this type of construction.

34.6.1.6

Concrete Immersed Tunnels

Concrete immersed tunnel elements will float with large drafts. Freeboard for concrete elements is
often less than 0.3 m, resulting in almost the entire element being underwater when towed into
position. This requires careful planning from the Contractor during the floating process. Paths from
the fabrication site to the tunnel alignment must contain water deep enough for the element to pass.
Therefore, concrete elements shall be cast in a basin constructed close to the Project site. A dredged
channel may be required from the basin to the tunnel alignment. Once the concrete elements have
been fabricated, the basin shall be flooded. These elements shall be towed out of the basin and to
the tunnel alignment.

Recent development in the use of materials and construction methods that reduce the number of the
construction joints shall be employed by the Contractor, who shall submit the mix design with
reduced water to cement ratio and reduced heat of hydration, both of which result in fewer through-
cracks during the curing of the concrete, to the Engineer for approval. Reducing the through cracks
is key to making the sections waterproof.

Concrete cast lengths in a single operation for a full-width segment, or bay, of a tunnel element shall
be approximately 20 m, despite the large volumes of concrete to be place and the expansion and
contraction that occurs during the first few days due to the heat of hydration.

To prevent cracking due to heat of hydration, mitigation measures shall be used including concrete
cooling using refrigerated pipes cast into the concrete; mix design; low-heat cement, such as ground
granulated blast furnace cement; shielding from the elements; and proper curing.

Typically, the floor slab shall be cast first, followed by walls and then roof. However, if techniques
have evolved permitting the outer walls and even the base slab to be cast with the roof slab, the
Contractor might be allowed to do that for reducing the number of construction joints in the exterior.
Since construction joints are particularly susceptible to leakage, most often due to thermal restraint,
it is most desirable to minimise their numbers. However, the Contractor shall ensure that all
construction joints are watertight.

Unless specified otherwise, prestressing may be used in certain cases to resist bending moments
and to reduce cracking. Tunnels may be prestressed transversely, or may have a nominal
longitudinal prestressing applied. Careful detailing and good workmanship shall be employed by the
Contractor to eliminate virtually all deleterious cracking in concrete.

34.6.2

Construction Methodology

34.6.2.1

General

The Contractor shall submit the construction methodology of the immersed tunnel in compliance with
Contract documents and requirements of the specifications of this section for the Engineer’s review
and approval. This construction methodology shall include excavating the open trench in the bed of

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-32

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

the body of water being crossed. Tunnel elements shall be fabricated off-site, at a shipyard or in dry
docks. Elements constructed on launching ways shall be launched similar to ships by sliding them
into the water. Elements constructed in dry docks, shall be floated by flooding the dry dock and the
ends of each element shall be closed by bulkheads to make the element watertight. Bulkheads shall
be set back a nominal distance from the end of the element, resulting in a small space at the ends
of  the  adjoining  sections  that  shall  be  filled  with  water  and  will  require  dewatering  after  the
connections with the previous element is made. After fabrication and launching, the elements shall
be towed into position over the excavated trench; once positioned and attached to a lowering device,
such as the lay barge, pontoons, or crane; ballast shall be placed in or on the element so that it can
be  lowered  to  its  final  position.  Ballasting  of  the  element  may  be  achieved  by  water  ballast  in
temporary  internal  tanks  or  by  adding  concrete.  After  placing  the  element  in  its  position,  the
connection  shall  be  made  between  the  newly  placed  element  and  the  end  face  of  the  previously
placed element or structure to which it is to be joined. Once the element is in its final position, butted
up against the adjacent element, the water within the joint between two elements shall be pumped
out. After any remaining foundation work has been completed and locking fill is in place, the joint
can  be  completed  and the  area made  watertight. Once  locking fill  is  in  position,  another  element
shall  be  placed.  Bulkheads  shall  be  removed,  making  the  tunnel  opening  continuous.  For  safety
reasons, the bulkheads at the joint to the most recently placed tunnel element shall be left in position.
Tunnels shall then be backfilled and a protective layer of stone shall be placed over the top of the
tunnel.

34.6.2.2

Trench Excavation

The Contractor shall use the most common method of excavation for immersed tunnels, such as the
use of a clamshell dredger. Sealed buckets shall be used for contaminated materials or to reduce
turbidity in environmentally sensitive areas. Cutter suction dredgers may be used to remove most
materials other than hard rock. Blasting may be required in certain areas, though it is highly
environmentally undesirable.

The  tunnel  trench  shall  be  dredged  to  longitudinal  profiles  and  bottom  widths  taking  potential
sloughing of the sides and accuracy of dredging into account so that the necessary bottom width
and  profile  can  be  maintained  during  lowering  of  the  elements  and  placing  of  the  foundation
materials.  Over-dredging  shall  be  avoided;  however,  over-dredged  areas  shall  be  refilled  with
materials conforming to the design requirements for foundation materials. Dredging shall be carried
out in at least two stages: the removal of bulk material and trimming, which shall involve removal of
at least the last 1 m above final dredge level. All silt, or other material that may accumulate on the
bottom of the trench, shall be cleared immediately before placing the element. Dredging methods
and equipment shall be designed by the Contractor to limit the dispersal of fine materials in the water.
Turbidity, silt curtains, or other measures shall be used where appropriate. Methods, materials, and
mitigation measures shall be used to avoid or reduce to acceptable levels the impacts of excavation,
filling and other operations on the marine environment.

Trench excavation in any waterway is an environmentally sensitive issue. Once the environmental
conditions have been set by the planning and permitting process, extreme care  shall be taken to
meet these conditions. Trench excavation underwater is a difficult and complex process that can be
complicated  by  contaminated  materials,  tides,  storms,  and  construction  restrictions  in  waterways
due to environmental concerns associated with fish migration and mating patterns and with ecology
and  marine  life.  When  scheduling  construction  activities,  environmentally  friendly  construction
techniques, equipment, and innovative methods for dealing with contaminants must be considered
by the Contractor for the excavation and backfill.

The Contractor shall determine locations, elevations and dimensions of all underwater utility lines
and marine structures in the area of the dredging and provide protection, if required. Excavations
shall be evaluated for stability using appropriate limit state methods of analysis. Temporary offshore
slopes shall be constructed with a minimum factor of safety of 1.3. Side slopes of the trench shall
not be steeper than 2 horizontal to 1 vertical in soil, nor steeper than 1 horizontal to 4 vertical in rock
provided the minimum specified factor of safety is achieved. The Contractor shall ensure that the
bottom of any excavation is stable. Excavation base stability shall be taken into account by the

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-33

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

Contractor against heave in any cohesive soils. Remedial measures, such as ground improvement,
may be required to provide stability of the excavation base against heave.

Disposal of dredge materials shall be handled by the Contractor in compliance with the requirements
of the Contract documents. Contaminated materials must be disposed of in special spoil containment
facilities, while uncontaminated materials, if suitable, can be reused for backfill. Materials for reuse
must be stored in areas where excess water can drain away.

34.6.2.3

Foundation Preparation

Once the trench excavation is complete, installation of the foundation shall begin. Two types of
foundations can be used in immersed tunnel construction; continuous bedding, screeded foundation,
or pumped sand; or individual supports.

a. Continuous Bedding

Continuous bedding shall consist of clean, sound, hard durable material with a grading compatible
with the Contract plans and design criteria. These include applied bearing pressure, the method with
which  the  bedding  is  placed,  and  the  material  onto  which  the  bedding  is  placed.  Foundation
thicknesses  shall  not  be  less  than  500  mm  and  preferably  less  than  1.4  m.  Gaps  between  the
underside  of  the  tunnel  and  the  trench  bottom  shall  be  filled  with  suitable  foundation  material.
Foundations can be prepared prior to lowering the elements (screeded), or they can be completed
after placing the elements on temporary supports in the trench (pumped sand); foundations formed
after  placement  shall  include  sand  jetting,  sand  flow,  and  grout.  For  a  screeded  foundation,  the
bedding shall be fine-graded with a screed to the line and grade required for section placement, or
a stone bed may be placed with a computer-controlled tremie pipe (scrading). Settlement analyses
for the immersed tunnel shall be performed by the Contractor and should consider compression of
the  foundation  course  placed  beneath  the  tunnel  elements.  Analyses  shall  also  be  performed  to
estimate the longitudinal and transverse differential settlement within each tunnel element, between
adjoining tunnel elements, and at the transitions at the ends of the immersed tunnel. Measures shall
be  taken  to  prevent  sharp  transitions  from  soil  to  rock  foundations.  Varying  the  thickness  of  the
continuous bedding can accomplish this. Alternately the tunnel structure shall be designed to resist
the load affects from the potential differential settlement of the subfoundation material.

b. Individual Supports

Individual supports shall consist of driven piles. Pile foundations shall be designed in accordance
with generally recognised procedures and methods of analysis. The piles shall be designed to fully
support all applied compression, uplift and lateral loads; and any possible down-drag, or negative
friction, loads from compressible soil strata. The load-bearing capacity, foundation settlement, and
lateral displacement shall be evaluated for individual piles and for pile groups, as appropriate. The
load capacity for bearing piles shall be confirmed by static or dynamic pile load testing, in accordance
with recognised standards. Piles and tunnel sections are usually detailed to be adjustable to fine
tune the horizontal and vertical placement of the tunnel. Once the tunnel sections are in their final
potions, the adjustment shall be locked off and a permanent connection between the tunnel and pile
may be made. Spaces between the bottom of the tunnel section and the bottom of the trench below
the tunnel section shall be then filled with granular material. This process must be carefully controlled
so that the bottom of the trench is not disturbed and that the void is completely filled. Since in most
cases, the weight of the tunnel section being placed is less than the weight of the soil it is replacing,
pile foundations are rarely used.

34.6.2.4

Tunnel Element Fabrication

For steel tunnels, fabrication shall be done by modules, each module being in the range of 5 m long,
spanning between diaphragms. Modules shall be then connected and welded together to form the
completed shell of the tunnel element. Electro-slag and electro-gas welding shall not be permitted,
and all groove and butt welds shall be full-penetration welds. Measures need to be taken to eliminate
warping and buckling of steel plates resulting from their local overheating during welding. Welds
must be tested by non-destructive methods; it is recommended that ultrasonic testing be

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-34

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

supplemented by X-ray, spot-check testing. In some cases, stress relieving may be necessary. Keel
concrete placement shall be done in such a way that it avoids any overstressing or excessive
deflections in the bottom shell and its stiffeners. All length and angular measurements for tolerances
need to be made while the structure is shielded from direct sunlight to eliminate errors due to warping
from differential temperatures.

Concrete  tunnel  elements  shall  be  constructed  in  a  number  of  full-width  segments  to  reduce  the
effects of shrinkage.  Segment joints may consist of construction joints with reinforcement running
through them, or they may be movement joints. All joints must be watertight. Tight controls on casting
and curing must be maintained to minimise cracking. Differential heat of hydration shall be controlled
by the use of high percentages of blast furnace slag to replace Portland cement or by using internal
cooling  system.  Where  concrete  segments  are  cast  with  movement  joints,  they  shall  be  joined
together using temporary or permanent post-tensioning to form complete elements at least during
transportation  and  installation.  Care  must  be  taken  to  ensure  that  long-term  movements  of  short
segments free to move are acceptable.

Tunnel elements shall be fabricated to be approximately 90 m to 120 m in length, each. Actual length
is a function of the capacity of the fabrication facility; restrictions along the waterway used to float
the elements to the construction site; restrictions at the tunnel, including accommodation of marine
traffic during construction, currents, element shape and the availability of space for an outfitting pier;
and the capacity of the equipment used to lower the elements into place.

All construction hatches and openings shall be sealed by welding or other secure means, upon
completion of concreting or other works for which they were required. Before the launching or floating
of elements, bulkheads, manholes, and doors shall be inspected to ensure that they are secure and
watertight. When no longer needed, any temporary access manholes through the permanent
structure shall be closed and a permanent seal made.

As tunnel elements are installed, the actual installed length of tunnel and position shall be monitored
so that any changes to the overall length of future tunnel elements and the orientation of the end
faces can be adjusted, as required to ensure fit with the actual surveyed positions of installed tunnel
elements. This is especially important prior to fabrication and placement of the closure, or last,
element.

34.6.2.5

Transportation and Handling of Tunnel Elements

Tunnel element stability must be ensured at every stage of construction, especially when afloat. In
checking tunnel elements for stability while floating, the Contractor shall pay due attention to effects
of variations in structural dimensions, including results of thermal and hydrostatic effects. Items to
consider include the following:

•

Sufficient freeboard for marine operations, so that tunnel elements are relatively unaffected,

even when waves run over the top. A positive buoyancy margin exceeding 1 percent is
recommended to guard against sinking due to variations in dimensions and the densities of
both tunnel materials and the surrounding water.

•

Lateral stability of the element using cross-curves of stability analysis should have a factor of

safety in excess of 1.4 of the area under the righting moment curve against the heeling
moment curve. A positive metacentric height, or static stability, exceeding 200 mm is also
recommended.

When a storm warning is issued, or forecast wave heights are expected to exceed operational limits,
all marine operations shall be ceased temporarily; and marine plant and floating tunnel elements
shall be sent to their designated storm moorings or shelters. It is recommended that an emergency
berth be identified for tunnel elements, preferably within or close to the placement site. Special
measures may be required to control tunnel elements in areas with currents or navigation channels.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-35

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

34.6.2.6

Lowering and Placing

After outfitting at their final destination, immersed tunnel elements shall be prepared for immersion
and lowering onto prepared foundations in a trench in the bed. Equipment used may typically be
provided on a purpose-built catamaran straddling the element. Other methods include the placement
of pontoons on top of elements, or cranes have sometimes been used.

To lower an element to its final position, it is usual for either a temporary ballasting system to be
used or for the element weight to be such that the element will itself have sufficient negative
buoyancy. The method of immersion must include the following:

•

Maintain stability, including control over the tunnel element, while it is lowered to its final

position.

•

Enable the negative buoyancy to be increased as necessary so that a minimum factor of

safety against flotation and overturning of 1.025 is obtained immediately after lowering.

•

Enable the negative buoyancy to be increased to give a minimum factor of safety against

flotation and overturning of 1.04 within a few hours of lowering and placing, ignoring
assistance from adjacent elements.

•

Maintain a vertical downward load of not less than 500 kN on every temporary seabed

support, if used, until the element is placed on its final foundation.

Calculations for the factor of safety may include items such as external ballast, for example concrete
blocks or internal ballast water tanks.

Lowering equipment shall be designed to enable the lowering operation to be effectively controlled
from a central control point and to make available at the central control accurate information on the
position of the element and the loads on the lowering and the holding lines.

Elements shall be lowered and butted up to preceding elements. Thereafter, the joint between them
shall be dewatered. A typical joint between elements includes watertight bulkheads, like dam plates;
watertight access bulkhead doors; joint seal and gaskets; dewatering equipment, including any
pumps and piping; location devices to guide the element horizontally and vertically into place relative
to the preceding element; provisions for shear keys, both horizontal and vertical; and vertical and
horizontal adjustment devices, such as wedges, jacks, and shims.

Tunnel elements shall be installed at an elevation that considers an allowance for settlement such
that after completion of the foundation works and all backfilling, they will be expected to be located
within a tolerance of 50 mm laterally and vertically from their theoretical location, or any such lower
figure on which the design methods are based. Allowances for settlement included in the
determination of the installation level shall be determined before installation. Notwithstanding the
above, the relative location laterally and vertically shall not be more than 25 mm across any joint.
Relative locations vertically across the terminal joints to other structures shall not exceed 50 mm.

Where foundation pads are used for temporarily supporting tunnel elements, any requirements for
preloading and all subsequent behaviour of the pads shall be determined. Effects of potential hard
spots beneath the tunnel element created by the foundation pads shall be evaluated. Settlement of
the foundation pads shall be measured from the time of installation through any period of preloading
until the tunnel element no longer requires support by the pads.

Permanent survey markers shall be needed within and on top of each element so that at any time
its position relative to its position at time of casting is known. Survey towers or other markers or
systems shall be needed so that the position of the element during lowering and placing is accurately
known.

34.6.2.7

Element Placement

Element placement is the most delicate of all operations involving immersed tunnel elements.
Weather window durations must be defined as well as go and no-go hold points. Where prevailing
currents could affect placing operations, the Contractor shall use a weather-forecasting modelling

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-36

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

system  to  forecast  the  required  window;  this  may  require  monitoring  of  the  hydrological  and
meteorological conditions concurrently to develop a forecasting model. Such a model shall provide
an  understanding  of the  relationship  between  observed flow  and  meteorological  and  hydrological
conditions. The last go and no-go decision shall be based upon the current waves, and other physical
conditions  staying  below  the  designed  upper  limits  with  a  statistical  probability  of  more  than  90
percent. In all cases, the actual current at the element position shall be checked immediately before
lowering and continuously observed during the lowering and placing operation.

Elements shall have sufficient negative buoyancy to maintain stability and control of the tunnel
element during immersion, so that the element can be lowered safely to its final position. Design
shall enable the negative buoyancy to be increased, if required, to give the minimum factors of safety
given in Article 34.6.2.1.

Valves for dewatering of immersed joints shall be operated from inside the previously placed tunnel
element. No watertight doors or hatches shall be opened until it can be confirmed that there is no
water on the other side. Access must be maintained to the inside of the first element that is placed
from the time when the element is placed until completion of permanent access through one of the
terminal joints. Where hydrostatic pressure exists on a temporary bulkhead, the next two bulkheads
shall remain in place

— with one at the remote end of the same element, and the immediately

adjacent one in the next tunnel element. Watertight doors in these bulkheads shall remain closed at
all  times  when  the  last tunnel  element  is  unoccupied  by  personnel. Watertight  doors  shall  not  be
opened  until  the  absence  of  water  on  the  far  side  has  been  confirmed.  Stability  of  the  installed
immersed  tunnel  elements  during  removal  of  temporary  ballast  and  joint  dewatering  must  be
controlled to ensure that necessary factors of safety are maintained for the element as a whole, not
only  for  the  ends  and  for  the  sides,  and  so  that  the  bearing  pressure  on  the  foundation  remains
approximately uniform.

After lowering and initial joining of each immersed tunnel element, its position shall be precisely
surveyed before the next element is placed. Settlement monitoring of tunnel elements shall be
carried out using the survey markers installed inside the elements. Levels shall be recorded weekly
until completion of backfilling of the subsequent element to ensure no remedial action is required
and monthly thereafter until settlement becomes negligible.

34.6.2.8

Backfilling

The Contractor shall take into account the suitability of excavated material for use as backfill and
shall ensure that backfill placed next to the immersed tunnel is placed uniformly on both sides of the
structure  to  avoid  imbalanced  lateral  loads.  Maximum  differences  in  backfill  levels  outside  such
structures  above  the  locking  fill  shall  be  1  m  until  the  lower  side  has  been  filled  to  its  final  level.
Elements  with  more  than  1  m  difference  in  backfill  level  shall  be  designed  to  accommodate  the
resulting transverse loads.

All fill materials subject to waves and currents shall be of appropriate size and type to prevent scour
and erosion. All underwater filling and rock protection material shall be placed in a way that avoids
damage to the waterproofing membranes, if present, or to the structure from impact or abrasion.
Materials shall be placed in even layers on either side of the tunnel to avoid unequal horizontal
pressures on the structures, and shall be placed by means of buckets or tremie.

Prior to, and during the placing of fill, the trench shall be checked for sediment, which shall be
removed if determined to be detrimental to the performance of the material being placed.

Backfill shall be provided around the tunnel. In seismic areas, where there is a risk of liquefaction,
the foundation and backfill shall be constructed as free-draining to prevent the development of
excess pore-water pressure during and following a seismic event. Armour protection, if needed, shall
be provided to prevent long-term loss of backfill at the sides and on top of the tunnel.

Backfill shall consist of the following:

•

Selected locking fill to secure the elements laterally.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-37

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

•

General backfill to the sides and top of the tunnel structure, also providing an impact-

absorbing/load-spreading layer above the tunnel.

•

A rock protection blanket generally above and adjacent to the tunnel to provide scour

protection.

•

Rock-fill, anchor-release bands at both sides of the tunnel if required.

34.6.2.9

Locking Fill

Selected locking fill shall be placed in the trench to a minimum level of half the height of each element
after  the  joint  to  the  adjacent  tunnel  has  been  dewatered.  Locking  fill  shall  extend  at  least  2  m
horizontally  from  the  tunnel  element  before  being  allowed  to  slope  down  not  steeper  than  1:2.
Locking  backfill  shall  be  placed  in  layers  of  uniform  thickness  not  exceeding  600  mm,  such  that
lateral and vertical forces on the tunnel element are minimised and no displacement of the element
occurs.  Placement  of  locking  backfill  shall  proceed  from  the  inboard,  or  jointed,  end  of  tunnel
elements and shall progress towards the outboard end of tunnel elements in a manner that produces
a uniformly dense backfill bearing tightly against the tunnel periphery.

Locking fill must be a granular, clean, sound, hard, durable material that will compact naturally and
that will remain stable under both nonseismic and seismic conditions, where required. It may include
crushed, sound rock or gravel. Well-graded, sub-angular sand may be included. Sand fill, if used,
must be free-draining.

34.6.2.10 General Backfill

General backfill shall be used to fill the remainder of the trench above the selected locking fill to the
underside of any protection layer, or to the pre-existing seabed level

— if no protection layer is used.

General backfill shall be placed by a method that avoids segregation or misplacement of the fill.

Properties of general fill must suit the proposed design and method of placing. General fill may
comprise soft cohesionless material that will remain stable. General fill must be free from clay balls
and be chemically inert. Often the dredged materials for the trench are suitable as general backfill.

34.6.2.11 Protection Blanket

Elevations of the top of the protection layer shall approximate pre-existing seabed levels unless
instructed otherwise; however, in certain situations, the top of the tunnel can extend above the
original seabed in an underwater embankment

— if permitted. In this situation, the protective blanket

shall be provided above the embankment backfill.

Rock protection blanket material shall consist of hard inert material, usually sound, dense, newly
quarried rock in clean angular pieces, well graded between 25 mm to 250 mm. These materials shall
be durable for at least the design life of the tunnel. Methods of placing this material must ensure that
the large-size stones do not penetrate the general backfill and must cause no damage to
waterproofing of the tunnel, if used. Protection layers shall not be placed by bottom dumping.

34.6.2.12 Anchor Release Protection

In navigable waters, anchor release protection shall be provided, if required, and if the tunnel cover
extends above the bed. Rock armour for anchor release bands shall be of sound, dense, newly
quarried rock in clean angular pieces and well graded. The intent of the anchor release protection is
to bring the anchor to the surface and choke the gape, or the space between the hook and the shank.
Anchor sizes shall be for vessels plying those waters. These material needs to be durable for at least
the design life of the tunnel.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-38

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

34.6.3

Water Tightness and Joints between Elements

34.6.3.1

External Waterproofing of Tunnels

External waterproofing for tunnel elements shall be considered for both steel tunnels and concrete
tunnels. This  waterproofing  shall  envelop  every  part  of  the  element  exposed  to  soil  or  water  with
materials impervious to the surrounding waters. For steel tunnels, the outer steel membrane shall
act  as  waterproofing  membrane,  while  for  concrete  elements  either  steel  or  synthetic  membrane
shall be used.  For steel waterproofing membranes used on either concrete or  steel elements, an
appropriate corrosion protection and monitoring system shall be used to ensure that the minimum
design thickness is maintained during the life of the facility or an added sacrificial thickness shall be
provided. Non-structural steel membranes shall measure no less than 6 mm thick.

Membranes shall be watertight and the materials used for concrete elements shall include two coats
of a spray-applied elasticised epoxy material; steel plates; and flexible PVC waterproofing sheet.
Minimum thickness shall be no less than 2.0 mm, and anchored to the concrete using T-shaped ribs.
Waterproofing system materials shall have a proven resistance to the specific corrosive qualities of
the surrounding waters and soils. The materials of the system shall be flexible and strong enough to
span any cracks that may develop during the life of the structure. Bituminous membranes shall not
be used. Waterproofing systems shall adhere at every point to the surfaces to which they are applied
so that, if perforated at any one location, water may not travel under it to another. Areas of free water
flow between the membrane and the underlying concrete shall be limited to no more than 10 m

, in

case of leakage. For a steel tunnel, the membrane could be the external steel shell, provided that
an adequate corrosion protection is provided either by cathodic protection or additional sacrificial
thickness. Steel plates shall be joined using continuous butt welds. All welds shall be inspected and
tested for soundness and tested for water tightness. Notwithstanding the provision of a membrane,
the underlying structural concrete shall be designed to be watertight.

Depending upon the type of waterproofing used, it may require protection on the sides and top of
the tunnel elements to ensure that it remains undamaged during all operations up to final placement
and during subsequent backfilling operations.

34.6.3.2

Joints

Joints between immersed tunnel elements shall be classified as follows:

a. Immersion Joint (or Typical Joint)

Immersion joints are the joints formed when a tunnel section is joined to a section that is already in
place on the seabed. After placing the new element, and joining it with the previously placed element,
the space between the bulkheads, or dam plates, of the two adjoining elements shall be then
dewatered. To dewater this space, a watertight seal must be made. A temporary gasket with a soft
nose, such as the Gina gasket, shall be used. Additionally, an omega seal or equivalent shall be
provided after dewatering the joint from inside the joint.

Figure 34-1: Gina-Type Seal

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-39

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

Figure 34-2: Omega-Type Seal

For immersion joints, the primary compression or immersion seal shall consist of natural or neoprene
rubber compounds. Cross sections used shall be the Gina type or equivalent. This consists of a main
body with designed load/compression characteristics and an integral nose and seating ridge. These
materials shall have a proven resistance to the specific corrosive qualities of the water and soils and
an  expected  life  no  shorter  than  the  design  life  of  the  tunnel  unless  the  gasket  is  considered
temporary.  For flexible  joints,  a  secondary seal shall  be required  in  case  of failure  of the  primary
seal. It shall be manufactured from chloroprene rubber to an overall cross section corresponding to
that  known  as  an  Omega-type,  the  materials  shall  have  proven  resistance  against  the  specific
corrosive qualities of the water and soils, oil, fungi and micro-organisms, oxygen, ozone, and heat.

It is essential that immediately after dewatering the chamber between the two bulkheads that an
inspection of the primary seal is made so that any lack of water tightness can be remedied. Similarly,
the secondary seal of a flexible joint shall be pressure tested up to the expected maximum service
pressure via a test pipe and valve to ensure that it too can function as required; after a successful
testing, the chamber between the seals shall be de-watered.

b. Closure or Final Joint

Where the last element has to be inserted between previously placed elements, rather than
appended to the end of the previous element, a marginal gap will exist at the secondary end. This
short length of tunnel shall be completed as cast-in-place, and is known as the closure or final joint.

Forms of the closure or end joint shall be dependent on the sequence and method of construction.
Closure joints may also be immersion joints, although details may need to be different. Potential
options for the closure joints include the following:

•

Place the last element between two previously placed elements and dewater one joint

between  the  newly  placed  element  and  the  one  of  the  previously  placed  elements.  Then
insert under water closure form plates and place tremie concrete around the closure joint to
seal it. This joint can then be dewatered and interior concrete can be completed from within
the  joint.  Other  methods,  such  as  telescopic  extension  and  wedge  joints,  have  been
developed to make the closure joint similar to the immersion joint.

•

Construct end, or terminal, joints first; lay the tunnel elements outwards from these and

complete the immersed tunnel with a special closure, or final, joints.

•

Construct one terminal joint first and lay all the immersed tunnel elements outwards from that

side and backfill over the top of the final element, using a soil-cement mixture

— or other

reasonably watertight material

— in the vicinity of the second terminal joint. Construct the

structures abutting the second terminal joint after the immersed tunnel is complete.

•

Lay and complete the immersed tunnel with or without a special closure joint and backfill at

the terminal elements using a soil-cement mixture, or other reasonably watertight material,
in the vicinity of both terminal joints. Construct the structures abutting the both terminal joints
after the immersed tunnel is complete.

c. Earthquake Joint

This shall be an immersion joint of special design to accommodate large differential movements in
any direction due to a seismic event. It shall also apply to a semi-rigid or flexible joint strengthened
to carry seismic loads and across which stressed or unstressed prestressing components may be
installed.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-40

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

d. Segment or Dilatation Joint

Moveable segment joints must be able to transmit shear across the joint, allowing dilatation and
rotation. Joints shall contain an injectable, rubber-metal waterstop

— as well as neoprene and

hydrophilic seals.

34.6.3.3

Design of Joints between Elements

All immersed tunnel joints must be watertight throughout the design life, and must accommodate
expected movements caused by differences in temperature, creep, settlement, earthquake motions,
and method of construction. Displacements in any direction shall be limited so that the waterproof
limits of a joint are not exceeded. Joint shear capability shall take into account the influence of normal
forces and bending moments on the shear capacity of the section; the design shall take account of
shear forces generated where the faces of the joints are not normal to the tunnel axis. Joints must
be ductile in addition to accommodating longitudinal movements. Tension ties may be used to limit
movement so that joints do not leak or break open, especially during a seismic event.

Axial compressions of tunnel elements and bulkheads due to depth of immersion shall be taken into
account in determining joint dimensions at installation.

Primary flexible seals at tunnel joints must be designed to take into account the maximum deviations
of the supporting frames relative to their theoretical location, the maximum deviation of the planes of
the frames, and any relaxation of the seal. Seals are required to have a minimum compression of 10
mm greater than the compression required to maintain a seal. Just in case an initial seal is not
obtained after immersion and joining, it may be advisable in some cases for the immersion joint to
be designed so that a backup method of obtaining an initial seal is available.

For flexible joints, a secondary seal, or Omega

–type seal, capable of carrying the full water pressure

shall be fitted across the inside of the joint and shall be capable of being inspected, maintained, and
replaced. Seals shall be capable of absorbing the long-term movements of the joint and secondary
seals shall be provided with a protective barrier against damage from within the tunnel. All joints in
the tunnel shall be finished to present a smooth surface.

Metal hardware in joints shall have a design life adequate to fulfil its purpose throughout the design
life of the joint. Nuts and bolts for primary and secondary seals shall be stainless steel. Plate
connections between elements shall be corrosion-protected to ensure that the design life is obtained.

Mounting procedures or mounting surfaces for the primary seal of immersion joints must allow for
fine adjusting and trimming of the seal alignment to compensate for construction tolerances. Gaskets
shall be protected from accidental damage until the time of immersion. All embedded parts; fixings,
including the bolts and their corrosion protection system; mating faces; clamping bars; and other
fixings must have a design life at least equal to that of the tunnel structure. Where clamping bars
and other fixings are used for the secondary seal, these need to have a design life at least equal to
that of the secondary seal. Gasket assemblies shall have provision for injection in case of leakage.

34.7

Tunnel Construction Engineering

34.7.1

Introduction

This work shall consist of mined/bored tunnel construction engineering; the engineering that must
go into the road tunnel Project to make it constructible.

Construction operations shall be guided by people experienced in the actual construction of these
underground works so that the Project is constructible. Schedules must be realistic and reflect all
the restrictions that are imposed on the Project, whether they are physical, political, or from a third
party.

Tunnels are long linear undertakings with few opportunities to perform the work at more than one
location. Tunnels are also a series of repetitive operations, each of which usually must be finished
before the next can be started.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-41

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

This uniqueness and the linear, repetitive nature of the work must be understood by the Contractor
to control and manage the Project to a successful conclusion.

Perhaps the most significant factor impacting schedule is the type of geologic material that the tunnel
will be mined through and the amount of ground and surface water that will be encountered or
crossed. Tunnels are mined through rock, soil, or a combination of both. The geology encountered
determines the tunnelling methods that will be used, the speed that the tunnel can be constructed,
and the types of specialised equipment that are required.

Geologic material can also present some unique health and safety concerns that must be accounted
for in the construction of road tunnels. Gas, petroleum, contamination, voids in the ground, hot water,
or large quantities of groundwater all pose safety concerns that must be addresses so that the
workers building the tunnels are provided an environment free of hazards.

Of similar importance to the tunnelling methods and hours of operation are the communities that the
tunnel will pass under, the locations of the major work shafts or portals from which the work will be
serviced and the streets through which the equipment, personnel and material will get to and from
the worksite as well as how the muck removed from the tunnel is disposed of.

All of these factors will have impacts on the schedule of road tunnels, and in fact, represent risks to
the Project. The Contractor shall acknowledge, allocate, and mitigate these risks. Dealing with these
risks shall be accomplished by the Contractor complying with the requirements of the Contract
documents.

34.7.2

Construction Staging and Sequencing

34.7.2.1

Construction Staging

The mined/bored tunnel construction Project requires land area to set up the Contractor's offices,
shops storage yards, muck storage piles, electrical substations, and many other space needs. It
therefore is logical that the more space that can be made available to the Contractor to locate needed
structures, store needed materials, and allow for the movement of materials and equipment into and
out of the worksite, the more efficient the operation will be. Property shall be acquired by the Owner
to provide the Contractor with adequate space for efficient operation.

The mined/bored tunnel construction Project serviced by shafts require room to excavate the shaft.
There shall be room all around the shaft to allow equipment access and easy flow of the work around
the shaft location. Adequate property shall be acquired by the Owner to locate the shaft for efficient
operation.

34.7.2.2

Construction Sequencing

Underground construction shall be a series of individual activities that must be completed before the
subsequent activities can start. This series of unique activities is then repeated and repeated until
the operation is complete. For tunnels that employ drilling and blasting to create the tunnel opening
the series shall be drill, load, shoot, muck, and support. Each round shall be drilled a certain length
or depth using a pre-engineered drill pattern. Once the drilling is done, the explosives shall be loaded
into the drill holes and wired up. Equipment and crews shall be then pulled back a safe distance from
the loaded face and the blast shall be shot. Exhaust gasses produced by the explosives shall be
removed from the face and fresh air shall be sent to the heading area. After around 30 minutes, the
crew shall be brought back into the area to scale or knock down any loose rock and remove the
excavated material or muck. Once the muck is removed, the initial tunnel support shall be installed
to make the excavated opening stable and safe for the crew to work under. The cycle will be complete
and the tunnel has been advanced some distance. When all of these activities have been completed,
the Contractor shall then start the next round.

In TBM excavated tunnels, there shall be a defined sequence of activities needed to advance the
heading. The TBM shall complete this series much faster than in drill-and-blast tunnels, but the
elements remain similar. TBMs shall cut into the rock or earth a certain distance at the same time
the muck is removed by conveyor to either waiting muck cars or to a continuous horizontal conveyor,

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-42

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

so  the  TBM  can  combine  these  two  operations  thereby  saving  time  and  speeding  up  the  tunnel
progress. After the end of the TBM's stroke, when the hydraulic pistons used to push the TBM cutting
head into the rock have a defined length, the excavation shall be stopped and the TBM readied to
start  the  next  excavation  cycle.  While  this  is  happening,  the  length  of  tunnel  that  has  just  been
exposed  must  be  supported  to  provide  a  stable  and  safe  opening.  TBMs  shall  be  configured  to
perform this support function concurrently with the excavation sequence, depending on the size of
the  tunnel  opening,  the  type  of  ground  being  excavated,  and  the  design  of  the  machine.  This
operation must be done before the next excavation cycle can begin.

Tunnels shall be stabilised for long-term use by placing an internal final concrete liner. This operation
shall contain a series of individual steps that must be completed in sequence before the next length
of tunnel can be lined.

34.7.3

Mucking and Disposal

Muck is the industry term for excavated material produced during the advancement of the tunnel. All
tunnel mining produces muck. This excavated material must be removed from the working face of
the tunnel so that the next advance can be made. Once the muck is produced, it must be removed
from the tunnel and finally disposed of in a legal manner or used as fill for some portion of the tunnel
Project or other project where it could have a beneficial use.

Muck is actually a broken-down state of the in situ material through which the tunnel is driven.
Because the natural material is disturbed by either blasting, cut with a TBM or road-header, or cut
out with a bucket excavator, the volume of muck removed actually is larger than the natural bank
material. This swell is usually approximated as 70 percent to 100 percent more in rock and 25 percent
to 40 percent for soil.

Excavated  material  must  be  removed  from  the  tunnel.  Methods  chosen  to  remove  this  material
depends on many factors, such as the diameter or size of the excavation, the length of the tunnel
excavated from any given heading, the material being moved, the grade of the tunnel being driven,
and whether the material is going to a shaft for removal or a portal. Horizontal conveyor belts shall
be used for large excavated tunnels that are longer than a few thousand meters and are excavated
by  a TBM.  Conveyors  shall  move  a  large quantity  of material quickly.  Conveyors  require  that  the
excavated material be of relatively uniform small size so that it will sit in the belt during the transfer
to  the  shaft  or  portal.  Conveyors  can  be  used  with  a  drill-and-blast  excavation  method  if  the
Contractor employs a crusher to make the drill-and-blast rock a more even and smaller consistency.
This crushing is necessary to ensure that the material sits nicely on the belt, is small enough that
when it is loaded onto the belt it does not damage or rip the belt material. Conveyors shall be limited
to a grade, or slope, less than 18 degrees to successfully transport muck. Conveyors shall transport
rock or soil, which must not be too wet

— or it will not transport well. Conveyors can also be used in

tunnels where there are curves in the alignment but this requires some special care and equipment.

Material that is too wet to carry on a conveyor belt shall be pumped out of the tunnel through a
pipeline from the TBM to the shaft or portal. This method shall be used on soft-ground tunnels where
the material is clay-like or where sufficient water

— and often, conditioners — is mixed with the

excavated material to make it slurry like.

For smaller tunnels excavated by a TBM, the Contractor shall choose to load the excavated muck
into rail cars and haul it out of the tunnel using locomotives. Rail haulage also has some limitations,
such as the grades are usually limited to less than 4 percent, a great amount of rolling stock is
required, and great care must be paid to maintaining the track.

Once the muck arrives at the shaft or portal, it must be off-loaded and then disposed. The shaft shall
be  a  vertical  hole  through  which  all  excavated  material  must  be  lifted  and  removed  and  through
which  all  material  required  for  the  tunnelling  operations  must  be  lowered  to  the  tunnel  level.
Additionally,  all personnel working on

— or inspecting — the tunnel must come in and out of this

shaft. There are many ways to transport the muck up the shaft. Muck cars shall be lifted one by one
up the shaft, dumped in a pile on the surface, and lowered back down to the tunnel. Muck cars can
be dumped into a hopper at the bottom of the shaft and then loaded into a bucket that is hoisted to

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-43

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

the  top  and  dumped  or  the  muck  from  the  hopper  could  be  loaded  onto  a  vertical  conveyor  and
conveyed  to  the  top  of  the  shaft  and  dumped  onto  a  pile  or  hopper.  Similarly,  the  muck  can  be
pumped  to  the  surface  and  deposited  on  a  horizontal  conveyor,  a  stockpile,  or  run  through  a
processing plant to remove the water and the residual dumped on a pile or into hoppers.

Portals shall provide easier access to a tunnel since they eliminate the bottleneck that the shaft
imposes. Muck is easier to remove at a portal because the track can be placed on the ground or on
an elevated trestle so that muck cars can be pulled outside to dump their loads onto a muck pile.

Any disruption in the muck removal operation will delay the start of the next round or the next
advance. If the Contractor cannot get rid of the muck, it cannot produce more. This is also true once
the muck reaches the surface. There shall be a place to store the muck that is brought out of the
tunnel until it can be loaded into trucks or rail cars and hauled away. Without this storage capability
on the surface, all muck brought out of the tunnel must immediately be loaded into surface trucks or
rail cars for disposal. If there is a holdup in the surface trucking or rail cars then no more muck can
be brought out and the tunnel advance must stop. This situation is called being muck-bound and
must be avoided at all costs. The more muck storage that is available, the more unlikely it will be for
the Project to become muck-bound. Worksites must be large enough to provide this storage cushion,
the larger a worksite the bigger the cushion. Special care must be taken to ensure a steady stream
of vehicles to remove the muck as it is produced, and to deliver workers and materials

— as needed.

Thought must also be given to the hours of operation allowed in the tunnel Project. If the hours of
operation for surface work are restricted, such as if surface work is not allowed after 10 p.m., then
to operate the tunnel 24 hours per day, there must be some place to store muck underground, and
construction noises must be kept below a threshold based on local ordinances and/or certain realistic
decibel levels.

34.7.4

Health and Safety

Construction engineering and safety shall go hand-in-hand. Underground construction is inherently
a dangerous undertaking. Work goes on in a noisy environment, in close quarters often with moving
heavy machinery. Careful attention must be paid to the layout of the worksites; workers must be
protected at all times. The overriding philosophy must be that,

“everyone goes home safely at the

end of their shift

.”

Every step of the operation shall be planned with safety in mind. Normal surface safety concerns are
also  appropriate  for  underground  construction.  Workers  must  be  safeguarded  from  falling  off  the
work  platforms  used  in  the  mining  process. Workers  must  be  protected  from  being  struck  by  the
moving  equipment  used  throughout  the  mining  process.  Workers  must  be  protected  from  being
electrocuted; however, there are also many additional hazards that workers must be protected from
and guarded against.

Work underground involves mining through rock or soil or a combination of both. To excavate the
opening required for the tunnel the natural properties of the ground are disturbed. The ground is
usually not a homogeneous mass but has been subjected to massive forces of nature and has been
altered. Once the opening has been excavated it must be supported in order for the workers to be
protected from falling material, collapse or other deterioration of the tunnel roof or crown. So, it is the
job of the Contractor to plan on making the tunnel opening stable to allow workers to move freely
and without concern of falling material.

Because tunnels are by definition below the surface, lighting of the workspace is an important part
of underground safety. OSHA has regulations governing all elements of working underground and
the Contractor must be familiar with them all. There are required levels of lighting for the actual work
locations as well as the previously excavated openings. It is important to remember that the tunnels
are long linear work places. As the tunnels are advanced more and more safety plant must be added
along with the productive support elements.

One of the more challenging aspects of tunnel safety is the fact that workers must be constantly
supplied with high quality breathable air. Again OSHA is specific in its requirements. Each person
underground must be supplied with 5.66 m3 per minute of air. Additionally, much of the equipment

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-44

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

underground shall be powered by internal combustion engines. Diesel fuel is the only fuel allowed
underground. OSHA also has specific requirements for the equipment and for the amount of air that
must be delivered to the underground for each and every piece of diesel equipment working
underground. This diesel air requirement is in addition to the requirement for each and every person
underground. Tunnel atmosphere quality must be tested on a regular schedule to ensure that
sufficient quantities of oxygen are present and that concentrations of undesirable gasses and by-
products of the internal combustion engines are controlled to acceptable levels.

Also tests must be performed on a regular basin to ensure that the air movement across the
excavated cross section is no less that 10 m per minute.

If  this  is  not  enough,  Mother  Nature  can  often  provide  challenges  to  the  safety  of  workers
underground.  There  can  be  gasses  underground  that  can  seep  into  the  tunnel  opening  after  the
excavation  operation.  These  gasses  can  be  poisonous,  like  hydrogen  sulphide,  or  explosive  like
methane.  Whenever  these  gasses  are  present,  or  suspected  to  be  present,  the  Contractor  has
additional  OSHA  requirements  to  be  aware  of  and  to  follow.  Extra  ventilation  will  be  required,  in
addition to the air needed for both people and diesel equipment and the required quantity can be
substantial.  Whenever  these  gasses  are  suspected,  there  are  extra  requirements  for  continuous
monitoring of the atmosphere with automatic shutdown of equipment should the gasses be detected
in concentrations higher than allowed.

Water entering the tunnel opening is also a safety issue. Most tunnels are excavated below the water
table, therefore, the opening acts like a big drain and any water running through the rock or contained
in the soil tends to collect in the tunnel. Water running through the tunnel bottom or invert can cause
several potential safety issues. Tunnels can be accessed by one or more shafts, by a combination
of shafts and portal or from a portal alone. It is desirable to drive tunnels uphill so that any water that
seeps into the excavated opening flows away from the working face by gravity. This water shall be
allowed to run in a ditch located at the side of the tunnel invert. Care must be taken that workers do
not step into or fall into this ditch. The higher the inflow of water into the tunnel the greater the
problem of safely conveying it back along the tunnel and finally out the shaft or portal.

Tunnels that are driven down hill have the problem that water flows to and accumulates at the
working face. This collected water must be removed from the work area by pumping. The water is
pumped through a pipe at the side of the excavation. This pipe must extend all the way to the shaft
or portal where it can be removed from the tunnel. Water can also enter the tunnel in sudden large
flows. These can be dangerous occurrences and any tunnel where this is a possibility extra care
must be taken in the planning for worker safety. Tunnels under bodies of water are of particular
concern for this risk of sudden large inflows of water.

Fires in tunnels are especially dangerous and can lead to extensive damage and risk to a worker's
safety and life. Awareness of this potential danger shall be the responsibility of the Contractor, which
shall plan to mitigate the risk at every stage of the Project. Most tunnels are driven from one point to
another from a single point of entry, which is what makes tunnel fires so dangerous and concerning.
The tunnel environment contains numerous potential sources of fire. Equipment can malfunction and
catch fire. Workers using welding or burning torches can set off a fire. Leaking hydraulic fluid or fuel
from equipment can be ignited by a stray spark or discarded cigarette. Conveyor belts used to
transport muck can build up heat from rubbing on or over something and ignite. All of these possible
fire risks, and more, must be addressed by the Contractor to minimise the possibility of a fire or to
minimise the potential damage and injuries resulting from a fire. Only retardant material and hydraulic
fluid shall be allowed on any underground equipment or material. Fire suppression systems shall be
required for all underground equipment, conveyor belt motors, and storage magazines. Vertical muck
removal belts shall be equipped with deluge water systems to dump large quantities of water on any
belt fire event.

Of  equal  importance  in  dealing  with  tunnel  fires  is  how  to  provide  for  the  safety  of  the  workers
underground.  This  can  be  accomplished  in  several  ways.  Rescue  chambers,  where  workers  can
take  refuge  in  a  fire,  shall  be  fully  equipped,  and  supplied  with  independent  air  supplies;  and
insulation shall be deployed along the tunnel as the tunnel is advanced. Of equal importance, the

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-45

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

tunnel can be planned with intermediate access points that can be fully equipped to be able to
remove workers from the tunnel, when the tunnel has been excavated past these locations.

34.7.5

Schedule

The importance of the development and use of a realistic schedule for all phases of the Project
cannot be overemphasised. It is critical for the Contractor to understand the relationships among all
the activities that go into the Project, as well as the needs and interests of all those who are affected
by the construction, testing, and commissioning of the work. With this understanding, the Project can
go forth in an orderly, predictable manner, which in the end benefits everyone.

The schedule is the road map of how the Project progresses through all the necessary steps. It is
required that a comprehensive schedule be developed by the Contractor during the early stage of
the Project. During this early stage, the Project must be assigned to each and every component such
as construction, testing, commissioning, start up, and any activity or phase that is important to the
Owner. As the Project develops, and more of the actual work and restrictions are known, the
schedule must be re-evaluated and updated to reflect this new knowledge. The schedule
development shall be a living process that is used and revised constantly to be of maximum benefit
to the Project.

Realistic time needed to accomplish all aspects of the Project must finally be reflected in the
schedule. It makes no sense to handicap the tool, or schedule, or the process by introducing artificial
or incorrect restrictions or by putting unrealistic expectations into the schedule. In fact, these
restrictions and incorrect assumptions always create problems later in the Project, usually in the form
of delays, claims, and higher costs. There can be a positive case made for the Owner to actually
build some float time into the schedule, if possible, so that there is some way to cushion the effects
of unknown occurrences that could impact the Project schedule.

Unrealistic schedules sometime might result from external forces, such as the desire to have the
Project  completed  in  time  for  an  upcoming  event.  These  external  forces  always  need  to  be
acknowledged and addressed on a case-by-case basis. They can wreak havoc on the schedule, but
they must be taken seriously. It shall be noted that throughout the Project's life, its schedule will be
at the mercy of these external forces. Having said this, the best, and only, way to begin the Project
is with a realistic, well-thought-out schedule. This will reduce the risk that the Owner will be called
on  to  defend  an  inaccurate  timeline  necessary  to  complete  the  Project.  It  is  important  for  the
Contractor to remember that the schedule numbers that are initially released to the public and the
Owner  are  the  same  numbers  the  Contractor  will  have  to  live  with  and  defend  throughout  the
Project's  life.  It  is  much  easier  if  these  schedules  are  reasonable  and  defendable,  backed  by
professional experience and industry standards.

Having realistic schedules produces a win-win situation for both the Owner, as well as the Contractor,
by eliminating or at least minimising the conflicts that can occur on the Project.

The schedule shall divide the work into discrete activities each with an amount of time needed for
completion. Each activity shall be quantified with the important items of work such as linear meters
of tunnel or cubic meters of concrete. Production rates shall be then applied to these activities and
quantities. These discrete activities can then be combined in sequences that depict the way the
Contractor anticipates the work to be constructed. These sequences can be linear or overlapping;
but at the end, a roadmap of all the elements of the Project shall be developed, how they fit together
and how long the Project is expected to take.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-46

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

NDEX

adverse effects, 10
angular distortion, 22

Architectural Damage

, 21

baseline conditions, 7
boom, 15
bored, 5, 37, 38
bulkheads, 28, 30, 32, 33, 35, 36, 37
calculations, 6
cathodic protection, 29, 35
chemical treatments, 11
circular, 6, 15, 21, 29
communication, 7, 11
condition survey, 12
construction method, 6
Contaminated materials, 31
curing, 6, 30, 32
curvilinear, 6
cut-and-cover, 5, 6, 9, 10, 11
cutterhead, 14, 15
deformation, 8
Design, 5, 6, 9, 10, 11, 17, 24, 25, 27, 33, 37
dewatering system, 10, 11
differential pressure, 11
dilatation, 37
displacements, 8, 17
double-shell tunnel element, 29
dredge materials, 31
drill-and-blast, 6, 7, 15, 38, 39
dynamic compaction, 24
environmental disturbance, 28
environmental impacts, 10
Environmental testing, 7
equipment, 5, 6, 8, 9, 11, 12, 13, 14, 15, 16,

18, 25, 27, 31, 32, 33, 37, 38, 39, 40

excavation support systems, 8, 9
existing structures, 7, 8, 10
explosives, 12, 13, 14, 38
External waterproofing, 35
fabrication, 6, 28, 29, 30, 32
factor of safety, 22, 31, 32, 33
Falsework, 5
fault zones, 18
fibber optic lines, 11
fill materials, 34
finishing, 6
fire-life safety, 7
Fires, 40
flexible support systems, 9
forms, 5, 18
freezing, 11, 19, 26

Functional Damage

, 21

gas lines, 11
Geologic mapping, 7
Geotechnical instrumentation, 7, 8
gripper, 14
ground characterization, 7
ground conditions, 6, 7, 8, 9, 15, 21, 24, 26
ground improvement, 23, 31
groundwater conditions, 7, 8
groundwater control measures, 9
Groundwater depression, 20
groundwater table, 7, 10
grouting, 11, 18, 21, 23, 24, 25, 26, 27, 28
handling, 6, 28
hazards, 8, 37, 39
heave, 10, 27, 31
high voltage cables, 11
horseshoe, 6, 15
hydrophilic seals, 37
immersed, 5, 6, 28, 29, 30, 31, 32, 33, 34, 35,

36, 37

Immersion joints, 35
Impervious retaining walls, 10
improvised floodable basins, 28
initial draft, 29
initial support, 6, 7, 16
injectable, 37
installation, 6, 7, 9, 15, 16, 17, 18, 24, 27, 31,

32, 33, 37

installation system, 6
Internal diaphragms, 29
internal finish, 6
jacked-box tunnelling, 6
laboratory testing, 7, 26
Lateral stability, 32
Lattice girders, 16, 17
lighting, 7, 40
lining, 6, 7, 8, 12, 14, 15, 16, 18, 19, 23
locking fill, 30, 34
Longitudinal joints, 27
Lost ground, 20
marine operations, 32
micropiles, 24
mined, 5, 24, 37, 38
monitoring, 7, 10, 16, 33, 34, 35, 40
Muck, 38, 39
New Austrian Tunnelling Method, 6, 15
non-shrink, 29
observation wells, 7
oil separators, 11

Perimeter Control

, 13

permeability, 10, 25, 26
Permeation grouting, 24

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 34-47

HAPTER

34:

OAD

UNNELS

First Edition -January 2018

piezometers, 7
Pilot tunnels, 7, 8, 18
placing, 6, 28, 30, 31, 33, 34, 35, 38
portals, 5, 6, 24, 38
power, 11, 14
precast concrete plates, 27
precast segments, 18
Precautions, 10
Pre-injection, 14
probing, 8
protection, 6, 7, 8, 12, 17, 29, 31, 34, 35, 37
pumped wells, 10
rectangular, 6, 29
re-injecting, 22
ribs and lagging, 17
rigid systems, 9
risk assessment, 22
risks, 7, 8, 29, 38, 40
road traffic, 11
rock, 5, 6, 7, 8, 12, 13, 14, 15, 16, 17, 18, 19,

20, 30, 31, 34, 35, 37, 38, 39, 40

Rock bolts, 17
Rock dowels, 17
rock mass, 13, 17
rock protection blanket, 34
Rock reinforcement, 6, 14, 16
rotation, 37
Round length, 15
safe limit, 22
samples, 7, 26
Sampling, 5
sandwich construction, 29
schedule, 37, 38, 40, 41
Sealed buckets, 30
secant pile, 10
segment, 14, 18, 30, 37
seismic loads, 36
self-consolidating, 29
Sequential Excavation Method, 6, 15
settlement, 8, 9, 10, 11, 20, 21, 22, 27, 31, 33,

34, 37

Settling basins, 11
sewer, 11
Shield, 14, 20
shield tunnelling, 20
shotcrete, 6, 15, 16, 17
single-shell immersed tunnels, 29
slurry walls, 10, 11
soft ground, 5, 6, 15, 19, 20, 25
Soil dowelling, 24
Soil movement, 9
Soil nails, 24
soldier piles, 11
spalling, 6
stabilization, 12, 23
steel interlocking sheeting, 10

steel tunnel liner plates, 27

Structural Damage

, 22

subsurface investigations, 7
surface blasting, 13
Test pits, 7
traffic operation and control, 7
treatment, 11, 23, 24
trench stability, 28
Tunnel blasting, 13
tunnel boring machine, 6
unanticipated conditions, 7
uncontrollable variables, 14
utilities, 7, 9, 11, 12, 26
ventilation, 7, 9, 14, 18, 40
vertical downward load, 33
vibrations, 8
vibro compaction techniques, 24
Walls, 7, 9
water, 7, 8, 9, 10, 11, 14, 15, 18, 19, 20, 22,

24, 25, 26, 28, 29, 30, 31, 32, 33, 34, 35, 36,
37, 39, 40

water pressures, 8, 18
water tightness, 35
waterstop, 37
wheel, 15

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page ii

HAPTER

35:

RIDGE AND

NDERPASS

OAD

ESTING

First Edition -January 2018

IST OF

ABLES

Table 35-1: Static Load Test - Load arrangement and required monitoring ................................ 35-4

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 35-1

HAPTER

35:

RIDGE AND

NDERPASS

OAD

ESTING

First Edition -January 2018

BRIDGE AND UNDERPASS LOAD TESTING

This chapter outlines standards and requirements that apply to bridge and underpass static load
testing activities for the Project. If required in the Contract documents, the dynamic load testing shall
be carried out in accordance with the Contract Particular Specifications.

The Contractor shall carry out static load tests on the bridge and underpass superstructures, as part
of the acceptance process of new bridges and underpasses, after completion of the bridge or
underpass. Static load tests shall verify that the bridge and underpass

’s actual structural behaviour

matches that of the theoretical design.

The Contractor shall complete the static load test, as well as the dynamic load test if required,
according to the provisions of this chapter and shall comply with any further requirements that the
Engineer will supply to the Contractor in due course. On receipt of the

Engineer’s further

requirements, the Contractor shall prepare a Method Statement and provide it to the Engineer for
approval.

35.1

Objectives

The purpose of the load testing is to evaluate the structural performance and functional adequacy of
the bridge and underpass tested as an exact full-sized model with an appropriate margin of safety.

35.2

Reference Standards and Codes

Standards and codes for bridge and underpass load testing shall be as specified in these
specifications, in the Contract documents, if any, and the following, in their latest edition:

ADQCC (TR-516) Road Structures Design Manual;

OSHA

Occupational Safety and Health Administration.

35.3

Definitions

"Design Live Load" means the Abu Dhabi Vehicular Load (ADVL) as defined in Road Structures
Design Manual (ADQCC TR-516), including the corresponding impact factor and multi-lane reduction
factor.

"Test Load" means the actual loads used at each stage of testing.

35.4

Static Load Testing of Bridges

35.4.1

General Guidelines

The Contractor shall carry out a static load test on the bridge in compliance with the following general
guidelines:

a. Load testing shall be performed after construction of the bridge is complete and all the

superimposed dead loads (such as pavement layers, parapets, and footways) have been
applied, but not sooner than 28 days after the pouring of concrete for the bridge deck.

b. The Contractor shall ensure that all the stress relieving operations for the bridge bearings are

completed before load testing.

c. The Contractor is responsible for ensuring the

bridge’s general and structural safety during

testing. This responsibility includes ensuring that the bridge does not exceed its elastic limit
and that tests do not damage the bridge or its components, including bearings and expansion
joints.

d. The Contractor shall predetermine the test Load patterns and positions on the bridge deck to

simulate load effects for which the bridge has been designed. The amount and configuration
of the test load applied during the test must produce internal forces (bending moments, shear,
and axial forces) and reactions at critical sections that equal the corresponding live load

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 35-2

HAPTER

35:

RIDGE AND

NDERPASS

OAD

ESTING

First Edition -January 2018

values in the bridge design. The Contractor shall place the test load in standard width design
traffic lanes, spaced across the entire bridge roadway width between curbs, at pre-marked
locations.

e. The Contractor shall provide sufficient supporting calculations for selected test load values,

patterns, and positions to enable simulation of the most critical cases.

f. During the static load test, the Contractor shall increase the test load (in at least four

increments) to achieve the predetermined design maximum live longitudinal sagging and
hogging (if any) moments in mid-spans, design maximum live longitudinal hogging at internal
supports, and maximum live reactions at supports.

g. Precast concrete blocks may serve as truck loads to achieve the required axle loads. Lorries

that are loaded with aggregates may also serve as truck loads if the required axle loads can
be achieved. The Contractor may apply concentrated loads to the deck by jacking against
dead weight. Load testing shall be carried out for every span, pier, and abutment.

h. Deflections and strains shall be measured accurately and at a sufficient number of

Measurement Reference Points (MRPs) where maximum deformations are expected to
produce sufficient data to plot the theoretical and measured deflected shapes of the structure.
The Contractor shall take measurements at least at one fourth of the middle spans, at one
fifth of exterior spans, and at the tops of piers and abutments. The Contractor shall take
measurements at each section at no fewer than two measurement points, one at the centre
line and one at the edge of the bridge deck slab.

i. After completing load testing, the Contractor shall carry out a bearing performance inspection

to ensure that no additional restraint is present. Vertical deflections and compression of
bearings and differential translations (that is, the temperature induced movements at
expansion joints) shall be well below the design (or manufacturer) limits.

35.4.2

Calculations Required before Load Testing

To ensure the

structure’s safety, the Contractor shall take the following actions before conducting

load testing:

a. Calculate the theoretical bending moment, shear, and deflection diagrams, and reactions for

each test load stage. Maximum values for these factors shall not exceed the corresponding
values under design live loads.

b. Longitudinal flexural stresses and shear stresses along the bridge shall be calculated at

critical sections and checked, so that they do not exceed the allowable stresses of the bridge
at any time during the test.

c. Calculate the theoretical deflections at all MRPs for each test load increment. These values

shall not exceed the corresponding values under design live loads.

35.4.3

Load Testing Procedures

The Contractor shall comply with the following procedures when testing the bridge

’s static load:

a. Three days before load testing, take temperature measurements every hour at the top and

underside of the bridge

’s deck slab (or the underside of its steel or concrete girder). Measure

temperature at a location that will produce average values for the whole bridge.

b. Gradually apply the test load, in no fewer than four increments, before reaching the full, final

load. At each test load increment, sustain the load for at least one hour before reading the
deflections. Apply the maximum test load for at least twelve hours.

c. After each load increment, measure deflection at all MRPs, including above piers and

abutments. These measurements shall not exceed the corresponding theoretical values
calculated for the same loading.

d. After each load increment, visually inspect the bridge at critical locations for the appearance

or widening of cracks and for any other unwanted consequences. After detecting any crack,
measure its length and width and determine its form and orientation.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 35-3

HAPTER

35:

RIDGE AND

NDERPASS

OAD

ESTING

First Edition -January 2018

e. After reading deflections and performing a visual inspection at each MRP, verify and

determine that the bridge is performing as expected and, consequently, decide whether to
continue or postpone testing.

f. After removing test loads, measure deflections again to verify that any permanent deflection

is minimal and within acceptable limits. The ratio of permanent irreversible deflection to the
total deflection shall not exceed (0.2).

g. At each stage of load testing, when reading deflections, measure temperature at the top and

bottom of the bridge

’s deck. In case of significant temperature effects, the theoretical

deflections due to temperature shall be calculated and considered in comparing of theoretical
and measured deflections.

35.4.4

Static Load Testing Method Statement

The Contractor shall submit a load testing Method Statement for the bridge to the Engineer at least
two months before the testing date. This statement shall include at least the following items:

a. The current status of the bridge to be tested

b. A Traffic Management Plan for managing traffic during the test

c. A load testing procedures

d. A discrietization for the bridge deck

’s MRP positions.

e. Descriptions of the types of dial gauge and strain gauge to be used, their locations, their

sensitivities, and other relevant information.

f. Description of the type of truck to be used in the testing, its load intensity, its type of load, its

maximum and incremental loads, and the corresponding axle loads with justification for
assumed axle loads (based on model specification). Required loading for static load testing
shall be as per Section 35.4.5 of this chapter.

g. Descriptions of test truck configurations (in longitudinal and transverse directions for each

test load); such descriptions shall include supporting calculations for selected truck
configurations.

h. Bending moment, shear force, and theoretical deflection diagrams with the reaction of

supports due to the test load.

i. A comparison between design live load moments, shears, reactions, and deflections and

their corresponding theoretical test load values at all MRPs. A load testing statements shall
include a comparison of deflections at each test load increment.

j. Any additional information that the Contractor considers useful for load testing.

k. Bearings performance inspection.

35.4.5

Required Loading and Monitoring for Static Load Testing

During static load testing, the Contractor shall move the load across the bridge in stages, as specified
in the method statement.

The

test’s load intensity shall replicate the Abu Dhabi Vehicular Load (ADVL) in accordance to Road

Structures Design Manual (ADQCC TR-516), applied to all the existing traffic lanes and the outer
hard shoulders. The load intensities that correspond to design live loads shall be based on the actual
geometry of the bridge to be tested by the Contractor.

The Engineer shall approve the detailed disposition of each vehicle at each stage.

The Contractor shall provide vehicles for these tests as indicated in their method statement or in
accordance with alternative directions from the Engineer (given that such alternatives achieve the
required load intensity).

The Contractor shall set up on site a calibrated weighing bridge and confirm the weight of all vehicles
used in the test.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 35-4

HAPTER

35:

RIDGE AND

NDERPASS

OAD

ESTING

First Edition -January 2018

The Contractor shall load the bridge on each span based on the actual geometry and as indicated
in the method statement. After obtaining approval from the Engineer for the precise location for the
front of each train of vehicles at each stage, the Contractor shall incorporate these locations into the
method statement. As a typical example, Table 35-1 provides the load arrangement and required
monitoring for a 5 span bridge.

Table 35-1: Static Load Test - Load arrangement and required monitoring

Test stage

Spans loaded

Duration

Elapsed

time

Monitoring

required

Spans (piers)

to be

monitored

6 hours

Type A

1,2

1 hour

7 hours

Type B

(1)

1,3

6 hours

13 hours

Type A

1,3

2,3

1 hour

14 hours

Type B

(2)

2,4

6 hours

20 hours

Type A

2,4

3,4

1 hour

21 hours

Type B

(3)

3,5

6 hours

27 hours

Type A

3,5

4,5

1 hour

28 hours

Type B

(4)

1. A value in parentheses indicates the Pier

’s number

At the start of each stage, the Contractor shall move the test load to ensure the gradual application
and removal of load. Halfway through each stage, such movement shall achieve the maximum load,
which shall be sustained for the remainder of the period.

The Contractor shall obtain approval from the Engineer in advance for any deviations from or breaks
in the schedule outlined in Table 35-1.

At all stages, the Contractor shall report to the Engineer any unanticipated events or delays, to which
the Engineer will, if appropriate, provide further instructions on how to proceed with load testing.

The Contractor shall supply all necessary facilities, access, measuring, and photographic equipment
to enable the Engineer to inspect critical locations during the test.

35.4.5.1

Monitoring Type A

The Contractor shall provide approved deflection measuring devices consisting of dial gauges with
an accuracy of ±1 mm and strain gauges. Such deflection measuring devices shall be placed at mid
span and over supports of the span being monitored, as directed by the Engineer. The Contractor
shall take readings at the start of each stage, when reaching the maximum load for each stage, and
at the end of each stage. Temperature readings shall be taken by the Contractor throughout the test
on the deck surface and on concrete in the shade at locations that have been approved by the
Engineer.

35.4.5.2

Monitoring Type B

The Contractor shall carry out visual inspection of key elements only, including bearings.

35.4.6

Static Load Testing Analysis Report

The Contractor shall prepare a comprehensive static load testing analysis report and submit three
(3) copies of the report to the Owner and the Engineer two weeks after completing load testing for
the entire bridge. This report shall include at least the following items:

a. Details of adopted procedures, load configurations, and a summary of all items mentioned

above in the method statement.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 35-5

HAPTER

35:

RIDGE AND

NDERPASS

OAD

ESTING

First Edition -January 2018

b. An interpretation of the test results.

c. A table with theoretical deflections (that is, design live load and test load) and measured

deflections for all MRPs and for each test load increment. This table shall also include
measured deflections after removal of each test load increment. The Contractor shall apply
linear interpolation between loaded and unloaded bridge measurements to remove the
effects of temperature from the measured deflections in this table.

d. Longitudinal theoretical deflections (design live load and test load) and measured deflection

curves along the bridge centreline for each test load increment.

e. Graphs that compare measured deflections to theoretical deflections at major MRPs (that is,

along the bridge

’s centre line at mid-span and support locations). A static load testing

analysis report shall include the slope of the compatibility line, which the Contractor can
derive from the deflection graphs.

f. Any local effects observed during testing.

g. Final analyses, conclusions, and recommendations.

h. Results of a performance inspection for bearings.

i. A statement of approval for the bridge load testing.

j. Statement that load testing verifies that the completed bridge complies with its design

requirements.

35.5

Static Load Testing of Underpasses

The Static Load Testing of underpasses shall be carried out in accordance to the same principles
and procedures stated for bridges. Any traffic lanes above the underpass deck shall be loaded as
stated for bridge traffic lanes. The loading shall be repeated along the underpass length sequentially
for the whole length of underpass or as agreed by the Owner.

In case of double underpasses, the unsymmetrical loading shall also be considered. The contractor
shall consider all safety issues and submit the load testing method statement including loading
procedure and instrumentation for approval of the Owner.

TANDARD

ONSTRUCTION

PECIFICATIONS

ART

–

OAD

TRUCTURES

Page 35-6

HAPTER

35:

RIDGE AND

NDERPASS

OAD

ESTING

First Edition -January 2018

NDEX

acceptance process, 35-1
actual geometry, 35-3, 35-4
actual structural behaviour, 35-1
analysis report, 35-4, 35-5
bearings, 35-1, 35-2, 35-4, 35-5
calculations, 35-2, 35-3
calibrated weighing bridge, 35-3
conclusions, 35-5
critical sections, 35-1, 35-2
Deflections, 35-2
Design Live Load, 35-1
dial gauge, 35-3
discrietization, 35-3
double tunnels, 35-5
dynamic load testing, 35-1
elastic limit, 35-1
equipment, 35-4
exact full-sized model, 35-1
expansion joints, 35-1, 35-2
flexural stresses, 35-2
footways, 35-1
Graphs, 35-5
inspection, 35-2, 35-3, 35-4, 35-5
internal forces, 35-1
interpretation, 35-5
load increment, 35-2, 35-3, 35-5

longitudinal sagging and hogging, 35-2
Measurement Reference Points, 35-2
Method Statement, 35-1, 35-3
new bridges, 35-1
parapets, 35-1
pavement layers, 35-1
Precast concrete blocks, 35-2
reactions, 35-1, 35-2, 35-3
recommendations, 35-5
stages, 35-3, 35-4
standard width design traffic lanes, 35-2
static load testing, 35-1, 35-3, 35-4, 35-5
strain gauge, 35-3
strains, 35-2
superimposed dead loads, 35-1
superstructures, 35-1
temperature measurements, 35-2
Test Load, 35-1
test Load patterns, 35-1
test truck configurations, 35-3
theoretical design, 35-1
traffic lanes, 35-3, 35-5
Traffic Management Plan, 35-3
truck loads, 35-2
tunnel deck, 35-5
underpass, 35-1, 35-5

Abu Dhabi, United Arab Emirates. STANDARD CONSTRUCTION SPECIFICATIONS (PART 2 - ROAD STRUCTURES, 2020) - page 22