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

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not visibly separated. Such areas will produce a hollow sound when tapped. These areas may be
referred to as delaminations or incipient spalls. Pipe experiencing this type of problem shall be
repaired or replaced.

32.7.7

Slabbing

Slabbing is a serious problem that can occur under high fills. It is a radial failure of the concrete that
occurs from straightening of the reinforcement cage due to excessive tension. Slabbing is
characterized by large slabs of concrete peeling away from the sides of the pipe and a straightening
of the reinforcing steel.

Any pipe experiencing slabbing shall be repaired or replaced.

32.7.8

End Section Drop-off

End drop-offs are caused by erosion of the material supporting the pipe sections on the outlet end
of the culvert barrel. If a drop-off occurs, the end section shall be reset.

32.7.9

Follow-up

If any repairs or remedial action is performed on the pipe, a follow-up inspection following the same
guidelines as outlined in Section 32.7, Field Inspection, shall be performed between one and two
years' time.

32.8

Surface Finish

Defects that indicate proportioning, mixing, and moulding not in compliance with the specification, or
surface defects indicating honeycombed or open texture that would adversely affect the function of
the pipe, shall be repaired or the pipe replaced.

32.9

Waterproofing

Waterproofing of culverts shall be as specified in the particular specifications, as approved by the
Engineer, and in compliance with the applicable requirements of Chapter 28, Waterproofing, of these
standard specifications.

32.10

Removing and Replacing Culverts

Where shown in the plans, or where designated by the Engineer, existing culverts shall be removed
and relaid in accordance with these specifications. Any culvert damaged by the Contractor

‘s

operations shall be replaced at the Contractor

’s expense. All joints of the pipe before being relaid

shall be cleaned so as to be free from all adhering material, including old mortar placed as a collar
or seal in the original construction. All culvert sections removed and not relaid shall become the
property of the Contractor.

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annular space, 32-3, 32-4
arch, 32-1, 32-7,

32-11

, 32-12, 32-13, 32-15,

32-16

Backfill material, 32-15, 32-16
backfill materials, 32-5
Bedding, 32-5, 32-7, 32-11, 32-12, 32-14
bell end, 32-14
bell holes, 32-14, 32-18
Bituminous plastic cement, 32-3, 32-4
blasting, 32-7
boulders, 32-7
box sections, 32-1, 32-7, 32-15
calculations, 32-2
cementitious, 32-3
certificate of compliance, 32-3
circular, 32-1, 32-7, 32-14
Compaction, 32-11, 32-12, 32-13
construction equipment, 32-16
construction traffic, 32-17
curing, 32-4, 32-6
delaminations, 32-18
Department of Transport, ii
design strength, 32-6, 32-15, 32-17
Deviations, 32-6
downstream, 32-14
efflorescence, 32-18
elliptical, 32-1, 32-7,

32-11

, 32-12, 32-13, 32-

End drop-offs, 32-18
erosion, 32-17, 32-18
Excessive damage, 32-6
exfiltration, 32-17
existing culverts, 32-19
Fine cracks, 32-6
floating, 32-16
follow-up inspection, 32-19
foundations, 32-7,

32-11

, 32-12

gasketed joints, 32-4
geotextile, 32-7
gradations, 32-7
gravel, 32-5, 32-15
Hairline longitudinal cracks, 32-18
hammer, 32-18

Haunch

32-11

, 32-12, 32-15

headwalls, 32-16
high fills, 32-18
honeycombs, 32-6
incipient spalls, 32-18
indentations, 32-18
infiltration, 32-7, 32-17
inlet end, 32-14
inspection personnel, 32-17
Inspection records, 32-18

installation, 32-2, 32-5, 32-6, 32-7, 32-11, 32-

13, 32-14, 32-15, 32-17, 32-18

Internal inspections, 32-17
interpretations, 32-11, 32-12
jetting, 32-15
Joint separations, 32-17
Leaking joints, 32-17
Lean concrete, 32-16
levelling, 32-7
lifting holes, 32-5, 32-6
Match marks, 32-5, 32-6
migration, 32-7, 32-17
Misalignment, 32-17
Mortar, 32-3, 32-4
movement, 32-15, 32-16, 32-17, 32-18
overfill materials, 32-15
pipe, 32-1, 32-3, 32-4, 32-7,

32-11

, 32-12, 32-

13, 32-14, 32-15, 32-16, 32-17, 32-18, 32-
19

Poor bedding, 32-18

Precast

, i, 32-1, 32-2, 32-5, 32-6, 32-7, 32-14,

32-15

precasting plant, 32-5
prestressing, 32-2
Ramps, 32-16
reinforced concrete, 32-1, 32-7, 32-15
reinforcement cage, 32-18
remedial action, 32-19
rock, 32-5, 32-7,

32-11

, 32-12, 32-14

Rubber, 32-2, 32-4
Sand, 32-3, 32-13
sealant materials, 32-5
settlement, 32-4, 32-17
Slabbing, 32-18
Soil, 32-1, 32-2, 32-11, 32-13, 32-14
soil fines, 32-7
soil symbols, 32-11, 32-12
Spalled areas, 32-5
Spalling, 32-18
structure backfill, 32-7
subtrench, 32-11, 32-12
Test specimens, 32-5
thickness, 32-7, 32-11, 32-12, 32-13, 32-15
thicknesses, 32-6, 32-7
tolerances, 32-3, 32-6
tongue end, 32-14
trademark, 32-5
trench conditions, 32-6
upstream, 32-14
visual examination, 32-18
visual observation, 32-17
Waterproofing, 32-19
watertight, 32-4

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33.1

General

This work shall consist of procuring a comprehensive access system for the long-term inspection,
operation, and maintenance of bridges, which shall conform to the requirements of the Contract
documents and these standard specifications.

If required by the Contract documents, the bridge access system shall include the following units, at
a minimum:

1. One vehicle-mounted mobile access platform, a Bucket Type Unit (BTU), for all surfaces

above deck level.

2. One vehicle-mounted mobile access platform, an Under-deck Type Unit (UTU), for all under-

deck surfaces.

3. All other supplementary equipment needed to meet the requirements for safe access to all

surfaces.

33.2

Reference Standards and Codes

Standards and codes for bridge access systems 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.

33.3

Overall Requirements

This system

’s purpose is to enable the Owner to conveniently and safely access all external surfaces,

components of the bridge, and all openings into the interior of the bridge for long-term inspection,
maintenance, and repair. This system shall be suitable for the complete repainting of the bridge,
except in areas where it can be shown to be more economical to use temporary scaffolding.

This system shall include all necessary documentation, spares, support facilities for the storage and
maintenance of the access system, and where specified by the Contract documents, garaging
facilities off-site.

Suppliers shall provide training services for operation and maintenance of the system and
maintenance support services.

33.4

Outline Specifications

Features described in this section are indicative of the facilities to be included and the performance
required of the units. Suppliers shall provide details of any alternatives or variations to these and the
advantages or limitations of its proposal. In all cases, suppliers shall remain responsible for ensuring
that the overall performance requirements for the complete system are satisfied.

33.4.1

Outline Specifications for Bucket Type Unit (BTU)

Vehicle-mounted mobile access platform for all surfaces above deck level shall be a bucket-type
system with a minimum load capacity of 250 kg and a minimum working area of 1.2 m by 1 m. The
BTU shall:

a. Be used primarily to gain access to all parts of the bridge above deck level (e.g., visual

inspection, routine maintenance of paint, access to feature lighting for routine maintenance),
as well as the feature lighting systems on the outside of the deck

b. Provide access to the piers below deck level from the ground or from a barge

c. Reach adequate height above the bridge deck level to serve its purpose

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Turntable base shall be rigidly mounted on the chassis main frame, and shall be rotatable by 270
degrees, configured to allow the unit to be lowered from either side of the vehicle and provide
maximum operational flexibility of use on the bridge. Main boom shall rotate approximately 45
degrees up and 20 degrees down, and shall be designed to bridge barriers and other obstacles of
up to 3 m height.

By  means  of  a  second  rotation track,  a  second boom  shall  be fixed to the  outer  end  of the main
boom. This boom shall telescopically extend with a vertical clearance of up to 4.5 m measured from
the bridge deck. It shall be  capable of being placed alongside the bridge in a vertical position.  By
means of irreversible worm gear, the second rotation track shall be capable of rotating 180 degrees.
Vertical  position  of  boom  shall  be  actuated  by  two  parallel  arms  (tubes)  in  combination  with  two
double-acting hydraulic cylinders to ensure that the parallel arms can be extended or returned. This
shall be sufficient to compensate for the transverse slope of the bridge deck.

Third boom shall be a telescoping boom with a maximum reach of 12 m under the bridge when the
second boom is in vertical position from the centre of the second rotation track. This boom shall be
actuated by a double-acting hydraulic cylinder.

Equipped with an access door, the personnel working bucket shall be attached to the third boom,
and shall be automatically maintained in a level position.

33.4.1.1

Stability

Stability of the BTU in operation with the unit lowered on either side of the vehicle shall be provided
by appropriate counterweights mounted on the turntable of the vehicle.

To minimize the concentrated load on the deck surface, a system of additional support wheels shall
evenly distribute the full vehicle weight on all axles. Air spring suspension shall be used to facilitate
movement of the vehicle on the bridge and absorb shocks when the machine is travelling on bumpy
roads.

Movements of the vehicle on the bridge during operation shall be self-propelled. Movements shall
be slow and well-controlled.

33.4.1.2

Controls

Complete set of controls shall be provided at the bucket. All the phases of deploying and retracting
the platform shall be easily surveyed. Auxiliary manual controls shall be located at the rotation frame
on the carrying vehicle, and shall rotate together with the rotation frame. Controls at the bucket shall
override the auxiliary controls on the vehicle.

33.4.1.3

Standard Equipment

Facilities shall include a hydraulic pump driven by the power take-off of the engine, a generator for
the power supply on the platform, a two-way intercom between the carrying vehicle and the work
platform, and an independent emergency hydraulic pump actuated by a 7 hp gas engine with
attached pump for returning the aerial device into the stowed position.

33.4.1.4

Safety Features

All functional elements of the aerial device shall be designed and constructed for structural and
operational safety for the operating crew and surroundings. BTU shall be designed, built, and tested
in accordance with the stringent international safety standards.

Safety features shall include, but shall not be limited to:

a. Overload protection by an automatic OFF-switch and acoustic signal

b. Emergency OFF-switches on the vehicle and at the work platform

c. Holding valves to prevent undesired movements of booms in case of hydraulic failure

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d. Independent, engine-powered emergency hydraulic pump to return the aerial device into the

stowed position on the vehicle

e. Warning placards to remind personnel of operational hazards and limits

f. Access steps and a platform bottom with anti-skid flooring and minimum 1.1 m-high safety

rails on the platform

g. Flashing lights on the vehicle

33.4.1.5

Operational Features

BTU shall be designed and built for safe, time-saving, and problem-free operations based on proven
designs with many years of service. It shall require the vehicle width only on one traffic lane or side
strip on the bridge, with a minimum obstruction of traffic flow, and it shall be rapidly erected or
removed on site without external assistance. At least one socket for single-phase power shall be
provided at the working platform for the use of inspection and maintenance tools and equipment.

33.4.2

Outline Specification for Under-deck Type Unit (UTU)

One vehicle-mounted mobile access platform for all under-deck surfaces shall be of an underbridge
type and shall have a platform (rather than bucket type). It shall be capable of being positioned on
either side of the bridge roadway and overreaching the roadway edge parapets and footways. It is
envisaged that the underbridge unit shall not be capable of providing inspection access to the entire
underside of the deck from one side only. It is therefore assumed that the platform area will be a
minimum of half bridge width by 1.4 m, and have a minimum working load of 250 kg.

33.4.2.1

System

Underbridge Type Unit (UTU) access equipment shall be mounted on a road vehicle equipped with
air-suspension rear axles to prevent shock and damage to the machine while travelling on uneven
roads.

Turntable base shall be rigidly mounted on the chassis main frame, and shall be rotatable by 90
degrees either way, configured to allow the unit to be lowered from either side of the vehicle and
provide maximum operational flexibility of use on the bridge. Main boom shall rotate approximately
45 degrees up and 20 degrees down, and shall be designed to bridge barriers and other obstacles
of up to 3 m height.

One vertical frame with a horizontal point of rotation for erection to approximately 95 degrees shall
be fixed to the rotation frame. Pivoting shall be achieved by means of two hydraulic cylinders to allow
a tolerance to compensate transverse sloping of the bridge deck.

Two parallel arms or another arrangement shall allow the unit to cross high barriers at deck edges.
Unhindered access from the vehicle to the lifting tower and platform shall be possible in any position
of the supports. Design shall ensure that the unit in the transport position remains within the
maximum allowable vehicle heights.

One second rotation track shall be mounted between the end of the lifting tower and the tower lower
part to allow rotation of the platform by 90 degrees to either side. Rotation motion shall be achieved
by means of irreversible worm gear.

For long platforms only, the work platform shall be divided into two or three sections. Second and
third segments shall be telescopically extendable until full platform length is obtained. To allow the
bridge piers to be circumnavigated without problems when the platform is fully-loaded, the work
platform shall be rotatable by two times 90 degrees. Sockets for single-phase electrical power shall
be provided on the platform.

Additional equipment such as work scaffolds or electrically operated inspection lifts shall be provided
for installation on the platform to make it possible to inspect hard-to-reach areas underneath the
bridge deck or between girders. Such scaffolds or lifts shall be of the folding type; therefore, do not
have to be dismounting for the road transport position of the UTU. Work platforms shall lie in parallel

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with the lifting tower when the UTU travels on the road. Inspection of bridge piers on their full length
shall be achieved by means of a pier inspection platform that can be lowered from the main platform.
All additional equipment required to meet the standard specifications shall be supplied.

33.4.2.2

Stability

Appropriate counterweights shall be mounted on the turntable of the vehicle to increase the stability
of the UTU in operation with the unit lowered on either side of the vehicle.

To minimize the concentrated load on the deck surface, a system of additional support wheels shall
evenly distribute the full vehicle weight on all axles. Air spring suspension shall be used to facilitate
movement of the vehicle on bridges and absorb shocks when the machine is travelling on bumpy
roads.

Movements of the vehicle on the bridge during operation shall be self-propelled. Movements shall
be slow and well controlled.

33.4.2.3

Control Stations

Control elements shall be suitably arranged and easily understandable, positioned in such a way
that all phases of deploying and retracting the platform can be easily surveyed. Standard control
units shall be located at the following locations on the UTU:

a. At the rear part of the vehicle for erection and removal

b. At the lower end of the lifting tower, for the movements of the platform:

•

Lifting and lowering

•

Rotation telescopic extension and retraction

In the driver’s cabin, for vehicle movements on the bridge and for steering

33.4.2.4

Standard Equipment

Equipment shall include:

a. Power take-off

b. Hydraulic pump driven by the power take-off

c. Generator for the power supply on the platform

d. Two-way intercom system for undisturbed dialogue between the bridge deck and the platform

e. Independent emergency hydraulic pump actuated by a 7 hp gas engine with attached pump

for returning the aerial device into the stowed position

33.4.2.5

Safety Features

All functional elements of the UTU shall be designed for structural and operational safety for the
operating crew and surroundings. UTU shall be designed and built in accordance with the stringent
international safety standards.

Safety features shall include, but shall not be limited to:

a. Overload protection by an automatic OFF-switch and acoustic signal

b. Emergency OFF- switches on the chassis, in the lifting tower, and on the platform

c. Independent emergency hydraulic pump allowing for folding up of the platform into the

transport position

d. Access route from the vehicle to the lifting tower, and a work platform secured by hand rails

and lifting tower construction

e. Platform with anti-skid flooring and a minimum 1.1 m-high safety rails

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f. Flashing lights on the vehicle

33.4.2.6

Operational Features

Design of the UTU shall be the result of many years of experience and practice-guided development.
It shall be designed and built for safe, time-saving, and problem-free operation.

Its operational features shall include, but shall not be limited to:

a. Dimensioning of the platform shall allow unencumbered inspection or maintenance work by

several persons simultaneously.

b. UTU shall require the vehicle width only on one traffic lane or side strip on the bridge, with

minimum obstruction of traffic flow.

c. Erection or removal times required shall be extremely short. On-site erection or removal of

UTU shall not require external assistance.

d. Tractors shall be removable from trailer-mounted units during operation on the bridge, for

use elsewhere.

e. Sockets for single-phase power shall be provided on the platform for the use of inspection

and maintenance tools and equipment.

f. Additional equipment, such as work scaffolds or lifts (optional), shall be capable of being

positioned along the full length of the platform.

33.4.2.7

Other Features

Other features of the UTU shall include, but shall not be limited to:

a. Outrigger stabilizers shall not be required.

b. Platform shall be capable of being lowered on both the left-hand side and the right-hand side

of the truck chassis.

c. Wide platform shall allow comfortable working conditions for the inspection crew. Platform

shall be capable of being raised under the bridge up to approximately 1.5 m from the bridge
deck.

d. Access shall be fully-protected from the bridge deck to the platform in all operating positions

of the platform.

e. Ladders, work scaffolds, or lifts used on the platform shall remain assembled for road

transportation. They shall be pivoted into the horizontal position on the platform floor and
remain embedded in the platform when in the stowed position on the truck chassis.

33.5

Method of Procurement

The Contractor shall prepare a list of suppliers able to provide the access system and technical and
contract documentation needed to request for proposals from suppliers. Proposals from single-
source suppliers shall be preferred, but proposals from two suppliers in a joint venture with joint and
several liabilities shall also be considered. On approval of a shortlist by the Engineer, the Contractor
shall obtain detailed technical and firm-priced proposals for the system, and shall prepare a report
on the proposals to the Engineer and obtain such supplementary information and proposals as may
be necessary for the proposals to be evaluated. This information should include drawings showing
the proposals for access to every surface and component.

Acting on instructions from the Owner, the Engineer shall select the supplier and impose such
additional requirements as deemed necessary for the systems.

The Contractor shall then procure the systems and supervise their manufacture, transportation,
receipt, storage, commissioning, testing, training, and acceptance by the Owner.

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33.6

Use of the Bridge Access System in the Work

Except by prior written agreement of the Engineer or as required for commissioning and testing of
the access system, the system shall not be used in any part of the work. Permission to use the
system for other purposes will only be granted in exceptional circumstances and will be subject to
guarantees, assurances, and payments to the Owner regarding such use.

33.7

Additional Quality Standards

33.7.1

Durability/Design Life

Design life of the system shall be 20 years with minimal maintenance in this period, except for repair
of normal wear and tear, all in accordance with current best industry practices for such systems.

33.7.2

Spares and Replacement Parts

Supplier shall provide a comprehensive list of spares and replacement parts, which shall fully identify
the item, its specifications, durability, and alternative sources of supply. This list shall identify whether
each component is of limited life (consumable or subject to wear), if an essential spare is needed for
contingency, or if the component does not require spares in stock.

33.7.3

Operating and Maintenance Documentation

Comprehensive training, operation, and maintenance manuals in both hard copy and digital format
are required in English and Arabic.

33.7.4

Support Services, Repairs, and Facilities for Same

Supplier shall provide all necessary support services on a scheduled and on-call basis for a minimum
period of 20 years.

33.7.5

Commissioning and Testing of Equipment

Before acceptance of the system by the Engineer, the system shall complete an agreed programme
of commissioning and testing.

33.7.6

Safety

All parts of the system and services shall comply with the requirements of current international safety
standards for operation and maintenance.

33.8

Warranties

Warranties and guarantees required in the supply contract shall be in accordance with the Owner

’s

instructions.

33.9

Material to be Provided by the Engineer

The Engineer shall provide existing computer-based drawings of the bridge and supplementary
information to establish the requirements for access and other information specified by the Owner,
which shall include terms to be included in the supply contract.

33.10

Programme

The Contractor shall prepare a programme for the procurement of the system in accordance with
the further instructions of the Owner.

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advantages, 2
Air spring suspension, 3, 5
barge, 3
bridges, 2, 5
bucket, 2, 3, 4
bumpy roads, 3, 5
commissioning, 7, 8
concentrated load, 3, 5
Control elements, 5
counterweights, 3, 5
deck level, 2, 3
Department of Transport, 2
Design life, 7
documentation, 2, 7
engine, 3, 4, 6
equipment, 2, 4, 5, 6
Erection, 6
external surfaces, 2
feature lighting, 3
Flashing lights, 4, 6
footways, 4
generator, 3
guarantees, 7, 8
Holding valves, 4
hydraulic cylinders, 3, 5
hydraulic pump, 3, 4, 6
independent emergency hydraulic pump, 4
irreversible worm gear, 3, 5
Ladders, 7
lifts, 5, 6, 7
limitations, 2
load capacity, 2
long-term inspection, 2
Main boom, 3, 4
maintenance, 2, 3, 4, 6, 7, 8
Movements, 3, 5
openings, 2
operation, 2, 3, 5, 6, 7, 8
operational hazards, 4
operational safety, 4, 6
performance requirements, 2
Permission, 7
piers, 3, 5
platform, 2, 3, 4, 5, 6, 7
power supply, 3, 6
procurement, 8
removal times, 6
repainting, 2
repair, 2, 7
routine maintenance, 3
safe access, 2
second boom, 3
self-propelled, 3, 5

shocks, 3, 5
Sockets, 5, 6
spares, 2, 7
Stability, 3, 5
static load testing, 2
storage, 2, 7
supplementary information, 7, 8
suppliers, 2, 7
support facilities, 2
temporary scaffolding, 2
testing, 7, 8
Third boom, 3
training services, 2
transportation, 7
Turntable base, 3, 4
underbridge, 4
under-deck surfaces, 2, 4
vertical clearance, 3
Vertical position, 3
visual inspection, 3
Warning placards, 4
Warranties, 8
wheels, 3, 5
work scaffolds, 5, 6, 7
working area, 3
written agreement, 7

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34.3.4.1

Dewatering at the Tunnel Face .................................................................... 34-16

34.3.4.2

Drainage Ahead of Face from Probe Holes .................................................. 34-16

34.3.4.3

Drainage from Pilot Bore or Tunnel .............................................................. 34-17

34.3.4.4

Grouting ....................................................................................................... 34-17

34.3.4.5

Freezing ...................................................................................................... 34-17

34.3.4.6

Closed-Face Machine .................................................................................. 34-17

34.3.4.7

Other Measures of Groundwater Control ..................................................... 34-18

34.3.5

Waterproofing of Tunnels in Rock ....................................................................... 34-18

34.4

Soft-Ground Tunnelling .............................................................................................. 34-19

34.4.1

Introduction ......................................................................................................... 34-19

34.4.2

Tunnelling-Induced Settlement ........................................................................... 34-19

34.4.2.1

General ........................................................................................................ 34-19

34.4.2.2

Sources of Settlement ................................................................................. 34-19

34.4.2.3

Settlement Calculations ............................................................................... 34-20

34.4.3

Impact on and Protection of Surface Facilities .................................................... 34-21

34.4.3.1

Evaluation of Structure Tolerance to Settlement .......................................... 34-21

34.4.3.2

Mitigating Settlement ................................................................................... 34-22

34.4.3.3

Structure Protection ..................................................................................... 34-22

34.4.4

Soil Stabilization and Improvement ..................................................................... 34-23

34.4.4.1

Introduction .................................................................................................. 34-23

34.4.4.2

Typical Applications ..................................................................................... 34-23

34.4.4.3

Reinforcement Methods ............................................................................... 34-24

34.4.4.4

Micropiles .................................................................................................... 34-24

34.4.4.5

Grouting Methods ........................................................................................ 34-24

34.4.4.6

Ground Freezing .......................................................................................... 34-27

34.5

Steel and Concrete Tunnel Liners .............................................................................. 34-27

34.5.1

Scope ................................................................................................................. 34-27

34.5.2

Description .......................................................................................................... 34-28

34.5.3

Materials and Fabrication .................................................................................... 34-28

34.5.3.1

General ........................................................................................................ 34-28

34.5.3.2

Forming and Punching of Steel Liner Plates ................................................ 34-28

34.5.4

Installation .......................................................................................................... 34-28

34.5.4.1

Steel Liner Plates......................................................................................... 34-28

34.5.4.2

Precast Concrete Liner Plates ..................................................................... 34-29

34.5.4.3

Grouting ....................................................................................................... 34-29

34.6

Immersed Tunnels ..................................................................................................... 34-29

34.6.1

Introduction ......................................................................................................... 34-29

34.6.1.1

Environmental Impact .................................................................................. 34-29

34.6.1.2

Types of Immersed Tunnel .......................................................................... 34-30

34.6.1.3

Single-Shell Steel Tunnel ............................................................................. 34-30

34.6.1.4

Double Shell Tunnel .................................................................................... 34-30

34.6.1.5

Sandwich Construction ................................................................................ 34-30

34.6.1.6

Concrete Immersed Tunnels ........................................................................ 34-31

34.6.2

Construction Methodology .................................................................................. 34-31

34.6.2.1

General ........................................................................................................ 34-31

34.6.2.2

Trench Excavation ....................................................................................... 34-32

34.6.2.3

Foundation Preparation ............................................................................... 34-33

34.6.2.4

Tunnel Element Fabrication ......................................................................... 34-33

34.6.2.5

Transportation and Handling of Tunnel Elements ........................................ 34-34

34.6.2.6

Lowering and Placing .................................................................................. 34-35

34.6.2.7

Element Placement ...................................................................................... 34-35

34.6.2.8

Backfilling .................................................................................................... 34-36

34.6.2.9

Locking Fill................................................................................................... 34-37

34.6.2.10

General Backfill ........................................................................................... 34-37

34.6.2.11

Protection Blanket ........................................................................................ 34-37

34.6.2.12

Anchor Release Protection .......................................................................... 34-37

34.6.3

Water Tightness and Joints between Elements................................................... 34-38

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ROAD TUNNELS

34.1

General

This work shall consist of constructing, fabricating, furnishing, and installing road tunnels conforming
to these standard specifications, requirements of the Road Structures Design Manual (ADQCC TR-
516), the American Association of State Highway and Transportation Officials (AASHTO) LRFD
Bridge Design

Specifications

, and the details shown in the Contract documents.

Road tunnels as defined by the AASHTO Technical Committee for Tunnels (SCOBS-T-20 Tunnels)
are enclosed roadways with vehicle access that is restricted to portals, regardless of the type of
structure or method of construction. These standard specifications further define road tunnels that
do not include enclosed roadway created by highway bridges, railroad bridges, or other bridges. This
definition applies to all types of tunnel structures and tunnelling methods such as cut-and-cover
tunnels, mined and bored tunnels in rock and soft ground, and immersed tunnels.

Whenever the Contract documents permit the Contractor to select the method or equipment to be
used for construction or any operation, it shall be the Contractor's responsibility to employ methods
and equipment that will produce satisfactory work under the conditions encountered, such that no
damage is imparted on completed or partially-completed work.

Falsework and forms shall conform to the requirements of Section 1.20.8 of Chapter 1, General
Requirements, of these standard specifications. Generally, all concrete shall be fully-supported until
the required strength and age has been reached.

Other work involved in the construction of road tunnels shall be as specified in the applicable
chapters of these standard specifications, particularly:

•

Chapter 1: General Requirements, of these Standard Specifications

•

Chapter 4: Concrete Works, of these Standard Specifications

•

Chapter 5: Reinforcing Steel, of these Standard Specifications

•

Chapter 21: Concrete Structures, of these Standard Specifications

•

Chapter 22: Prestressing Systems, of these Standard Specifications

34.1.1

Reference Standards and Codes

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

AASHTO LRFD

American Association of State Highway and Transportation Officials - Load
and Resistance Factor Design, Bridge Construction Specifications;

AASHTO LRFD

American Association of State Highway and Transportation Officials - Load
and Resistance Factor Design, Bridge Design Specifications;

AASHTO

Standard Specifications for Transportation Materials and Methods of Sampling
and Testing;

AASHTO SCOBS- Subcommittee on Bridges and Structures;
T-20 Tunnels

ADQCC (TR-516) Road Structures Design Manual;

ASTM

American Society for Testing and Materials;

FHWA

Federal Highway Administration;

FHWA (2005e)

Earth Retaining Structures. Publication no. FHWA NHI-05-046, National

Highway Institute, US Department of Transportation;

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FHWA (2005f)

Micropile Design and Construction Reference Manual, Publication no. FHWA
NHI-05-039 ;

OSHA

Occupational Safety and Health Administration.

Table 34-1 presents American Association of State Highway and Transportation Officials (AASHTO)
and American Society for Testing and Materials (ASTM) standards that are related to materials for
road tunnels. It also includes designations and titles.

Table 34-1: Designations and titles for AASHTO and ASTM standards that apply to road

tunnels works

AASHTO

Designation

ASTM

Designation

Title

ASTM D4435

–

Standard Test Method for Rock Bolt Anchor Pull Test

ASTM D4436

–

Standard Test Method for Rock Bolt Long-Term Load
Retention Test

34.1.2

Working Drawings

The Contractor shall submit complete shop drawings complying with the Contract plans and Contract
documents. When complete details are not provided in the Contract plans or Contract documents,
the  Contractor  shall  submit  working  drawings  including  shop  drawings  and  substantiating
calculations  of  the  proposed  road  tunnel  structure,  installation  system,  or  construction  method.
Construction,  fabrication  or  installation  of  the  structure  shall  not  begin  until  the  Engineer  has
approved  the  drawings.  Working  drawings  shall  show  complete  details  and  substantiating
calculations  of  the  structure,  as  well  as  the  materials,  equipment,  and  construction  methods
proposed.

Shop drawings and working drawings shall be submitted in advance of the start of the work to allow
for review, revision, and approval without delay to the work. Approval by the Engineer shall not
relieve the Contractor of any contractual responsibility.

34.1.3

Materials

Concrete materials, manufacturing, protection, handling and placing, finishing, and curing shall
conform to the applicable requirements of Chapter 4, Concrete Works, and

Chapter 21, Concrete

Structures, of these Standard Specifications

Class of concrete to be used in each part of the structure shall be as specified or shown on the
Contract documents. If not shown or specified, the Engineer will designate the class of concrete to
be used in consistent with the requirements of Section 21.17 of Chapter 21, Concrete Structures, of
these standard specifications, as applicable.

Materials and installation of reinforcing and prestressing steel shall conform to the applicable
requirements of Chapters 5, Reinforcing Steel, and Chapter 22, Prestressing Systems, of these
standard specifications.

34.1.4

Tunnel Shape and Internal Elements

Three main shapes of highway tunnels are considered in these specifications

– circular, rectangular,

and horseshoe or curvilinear. Unless specified in the Contract plans, the shape of the tunnel shall
be dependent on the method used to construct the tunnel and on the ground conditions. Rectangular
tunnels shall be constructed by either the cut-and-cover method, by the immersed method, or by
jacked-box tunnelling. Circular tunnels shall be constructed by using either a tunnel boring machine

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(TBM) or by drill-and-blast in rock. Horseshoe configuration tunnels shall be constructed using drill-
and-blast in rock or by following the Sequential Excavation Method (SEM), also as known as the
New Austrian Tunnelling Method (NATM).

Road tunnels shall be lined with concrete and internal finish surfaces in compliance with the Contract
documents.  Unless  otherwise  specified, some rock tunnels may  be  unlined,  except  at the  portals
and  in  certain  areas  where  the  rock  is  less  competent.  In  this  case,  rock  reinforcement  shall  be
provided. Rock reinforcement for initial support shall include the use of rock bolts with internal metal
straps and mine ties, un-tensioned steel dowels, or tensioned steel bolts. To prevent small fragments
of  rock  from  spalling,  wire  mesh,  shotcrete,  or  a  thin  concrete  lining  shall  be  used.  Shotcrete,  or
sprayed concrete, shall be used as an initial lining prior to installation of a final lining, or as a local
solution to instabilities in the rock tunnel. It shall be placed in layers with welded wire fabric and/or
with steel fibres as reinforcement. Inside surfaces shall be finished smooth without the fibres. Precast
segmental lining shall be used in conjunction with the TBM in soft ground and if specified in rock.
Segments shall be erected within the tail shield of the TBM. Segmental linings could be made of cast
iron, steel, and concrete. Unless otherwise specified, all segmental linings shall be made of concrete.
They shall be gasketed and bolted to prevent water penetration. Precast segmental linings could be
used as a temporary lining, where a cast-in-place final lining can be placed, or as the final lining.

Road tunnels shall be finished with interior finishes for safety and maintenance requirements
conforming to the Contract documents. Walls and ceilings shall receive a finish surface, while the
roadway shall be paved with asphalt pavement. Interior finishes shall be either mounted or adhered
to the final lining, and shall consist of ceramic tiles, epoxy-coated metal panels, porcelain-enamelled
metal panels, or various coatings. They shall provide enhanced tunnel lighting and visibility, provide
fire protection for the lining, attenuate noise, and provide a surface easy to clean.

Tunnels shall be equipped with various systems such as ventilation, lighting, communication, fire-
life safety, and traffic operation and control, including messaging and operation and control of the
various systems in the tunnel. The Contractor shall furnish and install these elements in accordance
with the details and provisions of the Contract documents and the applicable requirements of other
chapters of these Standard Specifications.

34.1.5

Additional Investigations during Construction

The Contractor shall perform additional subsurface investigations and ground characterization
during the construction of the tunnel Project. Such construction phase investigations shall serve a
number of important functions, providing information for:

a. The Contractor design and installation of temporary work

b. Further defining anomalies and unanticipated conditions identified after the start of

construction

c. Documenting existing ground conditions for comparison with established baseline conditions,

thereby forming the basis of any cost adjustments due to differing site conditions

d. Assessing ground and groundwater conditions in advance of the tunnel heading to reduce

risks and improve the efficiency of tunnelling operations

e. Determining the initial support system to be installed, and the locations where the support

system can be changed

f. Assessing the response of the ground and existing structures and utilities to tunnelling

operations

g. Assessing the groundwater table response to dewatering and tunnelling operations

h. Determining the location and depth of existing utilities and other underground facilities

The construction phase investigation program shall include the following elements:

1. Subsurface investigation borings and probings from the ground surface

2. Test pits

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3. Additional groundwater observation wells and/or piezometers

4. Additional laboratory testing of soil and rock samples

5. Geologic mapping of the exposed tunnel face

6. Geotechnical instrumentation

7. Probing in advance of the tunnel heading from the face of the tunnel

8. Pilot tunnels

9. Environmental testing of soil and groundwater samples suspected to be contaminated or

otherwise harmful

Some of the above investigation elements, such as geotechnical instrumentation, may be identified
as requirements of the Contract documents, while others, such as additional exploratory borings,
may be left to the discretion of the Contractor for its benefit and convenience. Tunnel face mapping
and groundwater monitoring shall be required elements for the tunnel Project, since the information
obtained from these records will form the basis for evaluating the merits of potential differing site
condition claims.

34.1.5.1

Geologic Face Mapping

With open-face tunnelling methods, including the SEM, open-face tunnelling shield in soil, and the
drill-and-blast method in rock, all or a large portion of the tunnel face shall be exposed, allowing a
visual assessment of the existing ground and groundwater conditions. In such cases, the exposed
face  conditions  shall  be documented  in  cross-section  sketches  (face mapping)  drawn  at frequent
intervals  (every  15  metres  minimum)  as  the  tunnel  advances  and  as  required  by  the  Engineer.
Information typically included in these face maps includes the station location for the cross-section;
the date and time the face mapping was prepared; the name of the individual who prepared the face
map; classification of each type of material observed; the location of interface boundaries between
these  materials;  rock  jointing  including  orientation  of  principal  joints  and  joint  descriptions;  shear
zones; observed seepage conditions and their approximate locations on the face; observed ground
behaviour  noting  particularly  the  location  of  any  instability  or  squeezing  material  at  the  face;  the
location  of  any  boulders,  piling,  or  other  obstructions;  the  location  of  any  grouted  or  cemented
material;  and  any  other  significant  observations.  In  rock  tunnels  where  the  perimeter  rock  is  left
exposed, sketches presenting similar information shall be prepared for the tunnel walls and roof. All
mapping shall be prepared by a geologist or geological engineer knowledgeable of tunnelling and
with soil and rock classification.

Face maps shall be used to accurately document conditions exposed during tunnelling, and to
develop a detailed profile of subsurface conditions along the tunnel horizon. However, there might
be limitations and considerable uncertainty in any extrapolation of the observed conditions beyond
the perimeter of the tunnel.

When  used  in  conjunction  with  nearby  subsurface  investigation  data  and  geotechnical
instrumentation  records,  the  face  maps  shall  be  used  to  develop  general  correlations  between
ground  displacement,  geological  conditions,  and  other  factors  (depth  of  tunnel,  groundwater
conditions, etc.).

34.1.5.2

Geotechnical Instrumentation

Geotechnical  instrumentation  shall  be  used  during  construction  to  monitor  ground  and  structure
displacements,  surface  settlement  above  and  near  the  tunnel,  deformation  of  the  initial  tunnel
supports and final lining, groundwater levels, loads in structural elements of the excavation support
systems, and ground and structure vibrations, among others. Such instrumentation shall be a key
element  of  any  program  for  maintenance  and  protection  of  existing  structures  and  facilities.
Additionally, it shall provide quantitative information for assessing tunnelling procedures during the
course of construction, and shall be used to trigger modifications to tunnelling procedures in a timely
manner  to  reduce  the  impacts  of  construction.  Instrumentation  shall  be  also  used  to  monitor  the

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deformation and stability of the tunnel opening and to assess the adequacy of the initial tunnel
support systems and the methods and sequencing of tunnelling, particularly for tunnels constructed
using the SEM and tunnels in shear zones or squeezing ground.

34.1.5.3

Probing

If applicable, such as for SEM and hard rock tunnelling projects, probing ahead of the tunnel face
shall be used to determine general ground conditions in advance of excavation, and to identify and
relieve water pressures in any localised zones of water-bearing soils or rock joints. For tunnels
constructed by using the SEM, probing shall also provide an early indication of the type of ground
supports that may be needed as the excavation progresses.

Probing shall be carried out to:

a. reduce the risks and hazards associated with tunnelling

b. provide continuous site investigation data directly along the path of the tunnel

c. provide information directly ahead of the tunnel excavation, allowing focus on ground

conditions of most immediate concern to tunnelling operations

Probing from within the tunnel must be considered as a supplementary investigation method, to be
used in conjunction with subsurface investigation data obtained during other phases of the Project.

Probing shall consist of drilling horizontally from the tunnel heading by percussion drilling or rotary
drilling methods. Coring can be used for probing in rock, but is uncommon due to the greater time
needed for coring. Cuttings from the probe holes shall be visually examined, classified, and assessed
for potential impacts to tunnel excavation and support procedures. In rock, borehole cameras shall
be used to better assess rock quality, orientation of discontinuities, and the presence of shear zones
and other important features.

34.1.5.4

Pilot Tunnels

Pilot tunnels (and shorter exploratory adits) shall be to the size specified in the Contract documents
for large size rock tunnels in complex geological conditions (typically at least 2 m by 2 m in size).

Pilot tunnels, if specified, shall provide the following:

a. Complete and reliable information for design of both initial tunnel supports and final lining, if

any

b. Access for performing in situ testing of the rock along the proposed tunnel

c. Information for specifying and selecting appropriate methods of construction and tunnelling

equipment

d. Effective means of pre-draining groundwater, and more confidently determining short-term

and long-term groundwater control measures

e. Effective means for identifying and venting gassy ground conditions

f. Means for testing and evaluating potential tunnelling methods and equipment

g. Access for installation of some of the initial supports (typically in the crown area of the tunnel)

in advance of the main tunnel excavation

Consideration shall also be given to locating the pilot tunnel adjacent to the proposed tunnel, using
the pilot tunnel for emergency egress, tunnel drainage, tunnel ventilation, or other purposes for the
completed Project.

34.1.6

Waterproofing

Tunnel waterproofing systems are used to prevent groundwater inflow into the tunnel structure
completely. They shall consist of a combination of various materials and elements. Unless detailed
in the Contract plans or specified in the particular specifications, the Contractor shall design and

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submit for the Engineer’s approval a tanked waterproofing system based on the understanding of
the ground and geohydrological conditions, geometry and layout of the structure and construction
method to be used, and in accordance with requirements of this chapter. The waterproofing system
shall be an integrated system that takes into account intermediate construction stages, final
conditions of structures and their ultimate usage including maintenance and operations.

34.1.7

Expansion and Contraction Joints

Joints are potential areas were leaks can occur. As such, they are potential sources of high
maintenance costs over the life of the tunnel. The number of joints shall be minimized and special
care shall be taken in the detailing of joints to ensure water tightness. The type and frequency of
joints required shall be in accordance with the details specified in the Contract plans and particular
specifications.

34.2

Cut-and-Cover Tunnels

34.2.1

Introduction

This work includes the construction and excavation support systems for cut-and-cover road tunnels.
It also includes maintenance of traffic and utilities, as well as control of groundwater during
construction.

34.2.2

Support of Excavation

34.2.2.1

General

The Contractor shall properly design and construct excavations for building cut-and-cover tunnels
as per Road Structures Design Manual (ADQCC TR-516), and applicable requirements of Chapter
20, Earth Retaining Systems, of these standard specifications, to provide a safe working space,
provide access for construction activities, and to protect structures, utilities, and other infrastructure
adjacent to the excavation. Design of excavation support systems shall be in consideration of a
variety of factors that affect the performance of the support system and that have impacts on the
tunnel structure itself. The Contractor shall consider these factors that are presented hereafter.

34.2.2.2

Monitoring of Ground Movement & Impact on Adjoining
Structures

The Contractor shall conduct the proper evaluation of soil movement as a result of the excavation
and mitigation of construction impacts on adjacent structures, facilities, and utilities. Soil movement
can be due to deflection of the support of excavation walls and ground consolidation.

a. Deflection of Support of Excavation Walls

Walls will deflect into the excavation as it proceeds prior to installation of each level of struts or
tiebacks supporting the wall. Deflections are greater for flexible support systems than for rigid
systems, are not recoverable, and are cumulative.

b. Consolidation Due to Dewatering

In excavations where the water table is high, it is necessary to dewater inside the excavation to avoid
instability. Dewatering inside the cut may lead to a drop in the hydrostatic pressure outside the cut.
Depending on the soil strata, this can lead to consolidation and settlement of the ground.

Existing buildings and facilities must be evaluated by the Contractor for the soil movement estimated
to occur due to the support wall movement during excavation. This evaluation depends on the type
of existing structure, its distance and orientation from the excavation, the soil conditions, the type of
foundations of the structure, and other parameters. The analysis shall be site specific. Empirical
methods and screening tools are available to more generally characterise the potential impacts.

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Existing buildings and facilities within the zone of influence must be surveyed and monitored by the
Contractor as directed by the Engineer. Measures to handle this issue shall include:

1. Design of stiffer and more watertight excavation support walls

2. Providing more closely spaced and stiffer excavation support braces and/or tiebacks

3. Use of pre-excavation soil improvement

4. Underpinning of existing structures

5. Providing monitoring and instrumentation program during excavation

6. Establishing requirements for mitigation plans if movements approach allowable limits

34.2.2.3

Base Stability

Poor soil beneath the excavation bottom may require that the excavation support structure be
extended down to a more competent stratum to ensure the base stability of the structure. This may
depend upon whether the earth pressures applied to the wall, together with its weight, can be
transferred to the surrounding soil through a combination of adhesion (side friction) and end bearing.

Soft clays below the excavation are particularly susceptible to yielding, causing the bottom of the
excavation to heave with a potential settlement at the ground surface, or worse, to blow up. High
groundwater table outside of the excavation can result in base instability as well. Measures to
evaluate the subsurface condition, and provide sufficient base stability must be addressed by the
Contractor. More details can be found in FHWA-NHI-05-046 "Earth Retaining Structure" (FHWA,
2005e).

34.2.3

Groundwater Control

34.2.3.1

Construction Dewatering

When  groundwater  levels  are  higher  than  the  base  level  of  the  tunnel,  excavations  will  require  a
dewatering  system.  For  cut-and-cover  construction,  the  dewatering  systems  will  depend  on  the
permeability  of  the  various  soil  layers  exposed.  Lowering  the  water  table  outside  the  excavation
could cause settlement of adjacent structures, impacts on vegetation, drying of existing wells, and
potential movement of contaminated plumes, if present. Precautions shall be taken by the Contractor
when dewatering the area outside of the excavation limits. Within the excavation, dewatering shall
be accomplished with impermeable excavation support walls that extend down to a firm, reasonably
impermeable stratum to reduce or cut-off water flow.

Impervious  retaining  walls,  such  as  steel  interlocking  sheeting,  concrete  secant  pile  or  concrete
slurry walls, shall be placed into deeper, less pervious layers, to reduce groundwater inflow during
construction and limit draw-down of the existing groundwater table. If excavation is performed under
wet  conditions,  then  the  water  shall  be  pumped  out.  Subsequent  to  the  excavation,  any  water
intrusion  shall  be  pumped  from  the  trench  by  providing  sumps  and  pumps  within  the  excavation.
Pumped pressure relief system may be required to prevent the excavation bottom from heaving due
to unbalanced hydrostatic pressure.

If approved by the Engineer, the Contractor may use pumped wells to temporarily lower the
groundwater table outside of the excavation support during construction; however, this may have
environmental impacts or adverse effects on adjacent structures. To minimise any lowering of the
water table immediately outside of the excavation, water pumped from the excavation shall be used
to recharge the water-bearing strata of the groundwater system by using injection wells. Provision
shall have to be made for disposal of water in excess of that pumped to recharge wells, probably
through settlement basins draining to storm drains.

After construction is completed, if there is a concern that the permanent excavation support walls
above the tunnel might be blocking the cross flow of the groundwater or may dam up water between
walls above the tunnel, the Contractor may be required to breach the walls above the tunnel at
intervals or removed to an elevation to allow movement of groundwater.

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34.2.3.2

Methods of Dewatering and Their Typical Applications

Groundwater shall be controlled during construction either by using impervious retaining walls (such
as concrete slurry or tangent pile walls, steel interlocking sheeting, etc.), by well-points drawing down
the water table, by chemical or grout injection into the soils, or by pumping from within the excavation.
Groundwater may be lowered, as needed, by tiers of well-points. Improper control of groundwater is
often a cause for settlement and damage to adjacent structures and utilities; consequently it is
important that the method selected is suitable for the proposed excavation.

Where the area of excavations is not too large, an economical method of collecting water is through
the use of ditches leading to sump pumps. Provisions to keep fines from escaping into the dewatering
system shall be made.

In larger excavations in permeable soil, either well points or deep wells shall be used to lower the
water table. The Contractor shall install test wells to test proposed systems. In certain cases, multiple
stages of well points, deep wells with submersible pumps, or an eductor system shall be needed.

34.2.3.3

Piping and Base Stability

In fine-grained soils, such as silts or clayey silts, differential pressure across the support of
excavation may cause sufficient water flow (piping) for it to carry fines. This causes material loss and
settlement outside, as well as a loss of integrity of soils within, rendering the soils unsuitable as a
foundation. In extreme cases, the base of the excavation may become unstable, causing a blow-up
and failure of the excavation support. This situation may be mitigated by ensuring that cut-off walls
are sufficiently deep, by stabilizing the soil by grouting, or freezing, or by excavating below water
without dewatering and making a sufficiently thick tremie slab to overcome uplift before dewatering.

34.2.3.4

Potential Impact of Area Dewatering

Dewatering an excavation may lower the groundwater outside the excavation and may cause
settlements. Lowering of the external groundwater can be reduced by the use of slurry walls, tangent
or secant piles, or steel sheet piling. Adjacent structures with a risk of settlement due to groundwater
lowering may require underpinning.

34.2.3.5

Groundwater Discharge and Environmental Issues

In  most  cases,  the  water  will  require  testing  and  possibly  treatment  before  it  can  be  discharged.
Settling basins, oil separators, and chemical treatments may be required prior to disposal. Excavated
material  itself  shall  require  testing  before  the  method  of  disposal  can  be  determined.  Material
excavated below water may need to stand in settling ponds to allow excess water to run off before
disposal.  Contaminated  material  may  need  to  be  placed  in  confined  disposal  facilities.  Local
regulations and permitting requirements shall dictate the method of disposal.

34.2.4

Maintenance and Protection of Traffic

When decking is required by the Contract documents or the Engineer to maintain the existing road
traffic, the support of excavation walls must be designed to handle the imposed live loads. Depth of
the walls may need to be determined by the necessity of transferring decking loads to a more
competent stratum below. This may depend upon whether the load applied to the wall, together with
its weight, can be transferred to the surrounding soil through a combination of adhesion (side friction)
and end bearing. Thick types of excavation support walls, such as slurry walls, drilled-in-place soldier
piles, and tangent piles, are much more effective than thinner walls, such as sheet piles or driven
soldier piles, in carrying the live loads to the bearing stratum.

Decking shall consist of deck framing and roadway decking. Deck framing shall be designed for Abu
Dhabi Vehicular Load (ADVL) in accordance to Road Structures Design Manual (ADQCC TR-516),
or for loading due to construction equipment that will operate on the deck, whichever is greater.

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34.2.5

Utility Relocation and Support

34.2.5.1

Types of Utilities

When  constructing  cut-and-cover  tunnels  in  urban  areas,  public  and  private  utility  lines  such  as
water,  sewer,  power,  and  communication  are  often  encountered.  Often,  utilities  are  not  located
where  indicated  on  existing  utility  information.  Therefore,  it  is  important  to  identify  and  locate  all
utilities in the field prior to excavation. Great care must be taken when excavating in the vicinity of
utilities, sometimes requiring that the final excavation to expose them is done by hand. Of particular
concern are those utilities that are movement-sensitive and those carrying hazardous substances.
These  include  large  diameter  water  pipes,  high-pressure  gas  lines,  fibber  optic  lines,  petroleum
pipes,  and  high  voltage  cables.  Some  utilities,  such  as  buried  high  voltage  lines,  are  not  only
extremely expensive to move but have very long lead times. Utilities such as sewers can present a
different problem; if gravity flow is used, diversions around a proposed tunnel may pose a serious
challenge. Some older water and sewer lines are extremely fragile, particularly if they are of brick or
cast iron construction.

34.2.5.2

General Approach to Utilities during Construction

It is not uncommon to divert utilities away from the proposed construction corridor. However,
diversion is not always possible, it may be too expensive, or a utility crossing may be unavoidable.
In such cases, it will be necessary to support the utilities in place. It is essential to have a coordinated
effort so that no interferences among the various utilities occur and that the construction can be
performed while the utilities are in place. Sometimes, utility relocations are performed in stages to
accommodate the construction requiring relocating the utility more than once.

Before the start of underground construction, the Contractor shall conduct a condition survey of all
utilities within the zone of potential influence of construction, making detailed reports for those that
may incur movements in excess of those allowable for the utility. Nature of any work required for
each utility shall be identified as protection, support, or relocation, and the date by which action is
required. It is essential that all utilities that need action are identified in sufficient time to allow the
construction to progress as programmed.

Supports may either be temporary or permanent. Depending upon the sensitivity of the utility being
supported, it may be necessary to provide instrumentation to monitor any movement so that remedial
action can be taken before damage occurs. Systems providing vertical support shall be designed by
the Contractor as bridge structures. Lateral support may be considered as retaining walls.

Most utilities require access for repairs; it is therefore required to have provisions for access to
utilities passing beneath a tunnel. In some cases, it has been found appropriate to relocate utilities
to a trough or utility tunnel in which all utilities can be easily accessed. In some cases, utilities cannot
be raised sufficiently to clear the tunnel roof slab; it may be possible to create a narrow trough across
the roof in which the utility may be relocated. In certain situations, utilities were passed through the
tunnel by providing a special conduit below the tunnel roof. In all cases, the Contractor shall carefully
coordinate all utility work with the utility owner.

34.2.6

Waterproofing of Cut-and-Cover Tunnels

Waterproofing of cut-and-cover tunnels shall be Type B waterproofing, as specified in the Contract
plans, and in accordance with the requirements of Section 28.3 of Chapter 28, Waterproofing, of
these standard specifications.

34.3

Rock Tunnelling

34.3.1

Introduction

This work includes the construction of rock tunnelling including excavation methods, excavation
supports, groundwater control, and other ground control measures.

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Because  of  the  range  of  behaviour  of  tunnels  in  rock,  such  as  from  a  coherent  continuum  to  a
discontinuum,  stabilization  measures  range  from  no  support,  to  bolts,  to  steel  sets,  to  heavily
reinforced concrete lining and numerous variations and combinations in between.  Certainly these
variations are to be expected when going from one tunnel to another, but often several are required
in  a  single  tunnel  because  the  geology  and/or  the  geometry  change.  Thus,  the  Contractor  must
recognise the need for change to allow for adjustments to be made in the field to adjust construction
means, methods, and equipment to the challenges presented by the vagaries of nature.

34.3.2

Rock Tunnelling Methods

34.3.2.1

Drill-and-Blast

The basic approach is to drill a pattern of small holes, load them with explosives, and then detonate
those explosives thereby creating an opening in the rock. Blasted and broken rock (muck) is then
removed and the rock surface is supported so that the whole process can be repeated as many
times as necessary to advance the desired opening in the rock.

By its very nature, this process leaves a rock surface fractured and disturbed. Disturbance typically
extends 1 m to 2 m into the rock and can be the initiator of a wedge failure. At a minimum, this usually
results in an opening larger than needed for its service requirement, and the need to install more
supports than shall be needed if the opening could be made with fewer disturbances. To reduce the
disturbance, the controlled blasting technique discussed in this section can be applied.

a. Controlled Blasting Principles

Explosives work by a rapid chemical reaction that results in a hot gas with much larger volume than
that occupied by the explosive. This is possible because the explosive contains both the fuel and the
oxidiser. When the explosive detonates, the rapidly expanding gas performs two functions

—

applying a sharp impulse to the borehole wall (which fractures the rock) and permeating the new
fractures and existing discontinuities (which pries the fragments apart). To deliver this one-two punch
effectively, the explosive is distributed through the rock mass by drilling an array of boreholes that
are then loaded with explosives and fired in an orderly sequence.

b. Relief

To effectively fragment the rock, there must be space for the newly created fragments to move into.
If there is not, the rock is fractured but not fragmented, and this unstable mass will remain in place.
Therefore, the geometry of the array of boreholes must be designed to allow the fragments to move.
This is optimum if there is more than one free face available. Creating an artificial "free face" is
discussed in this section under “Burn Cut”.

c. Delay Sequencing

To optimise the relief, internal free faces must be created during the blast sequence. To do this,
millisecond delay detonators separate the firing times of the charges by very short lengths of time.
Because of scatter in the firing times of pyrotechnic detonators, "long" period delays between holes
(on the order of hundreds of milliseconds) shall be used in tunnel and underground mining, to result
in blasts that last several seconds. This could change as more accurate electronic detonators are
developed.

d. Tunnel Blast Specifics

Tunnel blasting (like underground mine blasting) differs from surface blasting in that there is usually
only one free face that provides relief. To blast a large tunnel, an upper heading shall be blasted
first, and the rest of the rock is taken with a bench blast. Often, the whole face shall be drilled and
blasted in one event. An array of blast holes shall be drilled out using drilling equipment that can drill
several holes at once. Taking into account the rock type, the existing discontinuities in the rock
(joints, fractures, bedding planes), and of course the desired final shape of the tunnel, the pattern of
drill holes shall be determined before the blast.

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e. Burn Cut

Because the start of each cut with a solid face has no relief, several extra holes shall be drilled and
not loaded with explosives in the immediate neighbourhood of the initiation point. These burn holes
are generally larger than the explosively loaded holes, requiring an additional operation beyond the
normal drilling. Many different geometries of burn holes shall be used to optimise the cut, depending
on the rock type and joint patterns in a specific tunnel geology. These holes shall be fired first, with
enough firing time to allow the creation of a free face for the following holes to expand into.

Production Holes:

Following the initiation of the burn cut, the mass of the rock shall be fired in a

sequence so that the rock moves in a choreographed sequence, moving into the area opened up by
the burn cut, and out into the open space in front of the blast.

Wiring up the charges in the right sequence can be a challenging task in the confined environment
of a tunnel. The Contractor shall present the hook-up of the blast round, with the surface connectors,
and the period (corresponding to a specific delay time) next to each blast hole.

Desired sequence shall fire holes so that there is enough time for rock to move out of the way (create
relief), but not so much time that the rock surrounding unfired blast holes will fracture (creating a cut
off).

Perimeter Control:

It is important to blast so that the final wall is stable and as close to the designed

location as possible. Final holes shall be loaded more lightly, and called "perimeter holes" or "smooth
wall holes", and fired with some extra delay so that there is sufficient time for rock to fracture cleanly
and create little damage to the rock outside of the "neat" line (such damage is called over break).

Though fired after the production holes have been detonated, the smooth wall holes shall be fired
on the same delay period, creating a "zipper" effect of the holes generating a smooth fracture on the
perimeter.

Environmental Effects

– Vibration and Air blast:

Not all of the energy from blasting goes into

fragmenting rocks, some of it is unavoidably wasted as vibration that propagates away from the blast
area. This vibration can be cause for concern both for the stability of the tunnel itself, as well as
neighbouring underground and surface structures.

Air blast is an air pressure wave that propagates away from the blast site, due to movement of the
rock face and also possible venting of explosive gases from the boreholes. This shall not be so much
a problem in tunnelling, where personnel are evacuated from the blast area before a blast, but still
must be taken into account.

f. Blasting

– Art Versus Science

The Contractor shall study the scientific relationships between the properties of explosives, the
controllable variables such as the geometry of a blast and the timing, and uncontrollable variables
such as variations in rock type and existing jointing and fracturing. Many relationships can show the
most appropriate configuration of the blast holes, timing, and explosive type.

Experience, or the "art" of blasting, shall come into play in implementing the desired blast design.

34.3.2.2

Tunnel Boring Machines

TBMs shall excavate the rock mass in a form of rotating and crushing by applying enormous pressure
on the face with large thrust forces, while rotating and chipping with a number of disc cutters mounted
on the machine face (cutterhead).

a. Machine Types and Systems

TBMs shall be a full-face, rotational (with cutterheads) excavation machine that can be either gripper
or segment. There are three general types of TBMs suitable for rock tunnelling that the Contractor
may select from including open gripper/main beam, closed gripper/shield, and closed segment
shield.

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Open gripper/beam type of TBMs shall be selected for stable to friable rock with occasional fractured
zones and controllable groundwater inflows. Three common types of TBMs belonging to this
category could be used including main beam, Kelly drive, and open gripper (without a beam or Kelly).

Closed shield type of TBMs used for most rock tunnelling applications shall be selected for friable to
unstable rocks, which cannot provide consistent support to the gripper pressure. Closed shield type
of TBMs can either be advanced by pushing against segment or gripper. Although these machines
are classified as a closed type of machine, they are not pressurised at the face of the machine, and
cannot handle high external groundwater pressure or water inflows. The Contractor shall select the
most proper shielded TBMs for rock tunnelling. Shielded TBMs include single shield, double shield,
and gripper shield.

b. Machine Main and Support Elements

Main body and other supporting elements of the TBM shall be comprised of mechanisms for cutting,
shoving, steering, gripping, shielding, exploratory drilling, ground control and support, lining erection,
spoil (muck) removal, ventilation, and power supply. Main body of the rock TBM (either open or
closed) shall include some or all of the following components:

•

Cutterhead and support

•

Gripper (except single shield TBM)

•

Shield (except open TBM)

•

Thrust cylinder

•

Conveyor

•

Rock reinforcement equipment

Additionally, the main body of the TBM shall be supported with a trailing system for muck and
material transportation, ventilation, power supply, etc.

c. Compatible Ground Support Elements

Most ground support elements discussed in Section 34.3.3 can be specified with the use of hard
rock TBMs, especially if the TBMs are manufactured specifically for the Project.

•

Rock reinforcement by roof bolting

•

Spiling/forepoling

•

Pre-injection

•

Steel ring beams with or without lagging (wire mesh, timber, etc.)

•

Invert segment

•

Shotcrete

•

Precast concrete segmental lining

•

Others

34.3.2.3

Road Headers

Typical TBMs cut circular tunnels, which are the most practical cross section, but not always the
cross section that provides the most useable volume as a proportion of the total volume excavated.
The Contract shall use a specialised machine with the proper head that can cut the most favourable
shape, which can be more efficient in providing useable volume.

Another approach to cutting an opening closer to the actual required section is the road header.
Cutting tool for the road header shall be a very large milling head mounted on a boom, which boom,
in turn, is mounted on tracks or within a shield. Corners must be cut to the curvature of the milling
head, but the rest of the walls, crown, and invert can be cut to almost any desired shape. Single road

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header shall be capable of cutting variable or odd shapes that otherwise shall require TBM
excavation in combination with drill-and-blast or drill-and-blast itself.

Because of their adaptability, availability (a few months rather than a year or longer), and lower cost,
road headers shall be the method of choice for relatively short tunnels, approximately less than 1,600
m long, and for rock with an unconfined compressive strength less than 138 MPa.

The following is a general list when road headers shall be considered:

•

Rock strength below 138 MPa

– preferably below 103 MPa

•

Short runs, one-of-a-kind-openings

•

Odd, non-circular shapes

•

Connections, cross passages, etc.

•

Low to moderate abrasivity

•

Preferably, self-supporting rock

•

No or small inclusions

– chert, etc.

•

Nominal water pressure

34.3.2.4

Other Mechanised Excavation Methods

Other  mechanised  excavation  methods  that  are  being  developed  by  specialised  equipment
manufacturers  shall  be  proposed  by  the  Contractor  to  address  specific  issues  in  mining  and  civil
applications. One good example of a development such as the "mobile miner" developed by Robbins
as  a  "non-circular  hard  rock  cutting  system  to  be  applied  to  underground  mine  development"
(Robbins, 1990). The mobile miner is described as follows:

A boom mounts a large cutter wheel with a transverse axis having rows of cutters arranged only on
the periphery of the wheel. As the boom is swung from side to side, an excavated shape is generated
with a flat roof and floor and curved walls. Although the prototype machines have operated only with
this side-swinging action, to cut openings which are better suited to vehicular tunnels, the cutterhead
boom must be elevated up and down and at the same time swung from side to side. In this way a
horseshoe-shaped excavation can be generated.

34.3.2.5

Sequential Excavation Method/New Austrian Tunnelling
Method

SEM/NATMs offer flexibility in geometry that can accommodate almost any size of opening. Regular
cross sections involve an ovoid shape to promote smooth stress redistribution in the ground around
the  newly  created  opening.  By  adjusting  the  construction  sequence  expressed  mainly  in  round
length, the timing of support installation, and the type of support the chosen method will allow for
tunnelling  through  rock,  soft  ground,  and  a  variety  of  difficult  ground  conditions.  Additionally,
depending on the size of  the opening and quality of  the ground, the tunnel cross section may be
subdivided into multiple drifts.

Application of the SEM shall involve practical experience, earth and engineering sciences, and
skilled execution. The SEM tunnelling process addresses the following:

a. Ground and excavation and support classification based on a thorough ground investigation.

b. Definition of excavation and support classes by the following:

•

Round length, including maximum unsupported excavation length;

•

Support measures, including shotcrete lining and its reinforcement, ground reinforcement

by bolts, or dowels in rock;

•

Subdivision of the tunnel cross section into multiple drifts or headings, as needed,

including top heading, bench, invert, and side wall drifts;

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•

Ring closure requirements;

•

Timing of support installation, including typically every round;

•

Pre-support by spiling, fore poling, and pipe arch canopy; and,

•

Local, additional, initial support by dowels, bolts, spiles, face support wedge, and

shotcrete.

c. Instrumentation and monitoring.

d. Ground improvement measures prior to tunnelling.

34.3.3

Types of Rock Reinforcement and Excavation Support

34.3.3.1

Excavation Support Options

Initial support, sometimes called temporary lining, or temporary support of excavation, in rock
tunnelling keeps the opening open, stable, and safe until the final lining is installed and construction
is complete. As a consequence, the initial support system in a rock tunnel shall be one or a
combination of a number of the following options:

•

Rock reinforcement, such as rock dowels, bolts, and anchors;

•

Steel ribs;

•

Wood or other lagging;

•

Lattice girders;

•

Shotcrete;

•

Spiles or forepoling;

•

Concrete;

•

Re-steel mats;

•

Steel mats;

•

Cables;

•

Precast concrete segments; and,

Rock reinforcement, steel ribs, wood or other lagging, lattice girders, and shotcrete are the most
common support options; and, of those, a combination of rock bolts or dowels and shotcrete is the
single most common. In good, or better, rock tunnels, modern rock bolting machines provide rapid
and adjustable support close to the heading by knitting and holding the rock, or ground, arch in place
— thus taking maximum advantage of the rock's ability to be self-supporting. Preferably, shotcrete
is added a diameter or so behind the face, where its dust, grit, and flying aggregate are not a problem
for workers and equipment at the heading. Where there is a concern with smaller pieces of rock
falling, the system can be easily modified by adding shotcrete closer to the face or by embedding
any of a number of types of steel mats in the shotcrete.

Where the rock quality is lower, the Contractor may replace steel ribs with lattice girders. Like steel
ribs, the lattice girders form a template for the shotcrete and spiling. Lattice girders differ from steel
ribs in that they are lighter and can be erected faster. To provide the same support capacity, the
lattice girder system may require nominally more shotcrete measuring an additional 12.5 mm to 25
mm, which is more than compensated for by the easier and faster erection. To avoid using additional
shotcrete, the Contractor may use steel fibre-reinforced shotcrete instead. Additional fibre does not
change the compressive strength significantly, but it does produce a significant increase in the
toughness or ductility of the shotcrete.

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34.3.3.2

Rock Reinforcement

Rock reinforcement, including rock dowels and bolts shall be used to hold loose, or key, blocks in
place; or to knit together the rock (ground) arch that provides the support for the opening in rock.
Dowels and bolts are similar but the differences in their behaviour can be quite significant. Unless
otherwise indicated in the Contract plans or specified in the particular  specifications, rock dowels
and  rock  bolts  shall  be  high  yield  threaded  bars  galvanized  in  accordance  with  Section  23.4.10,
Chapter  23,  Steel  Structures,  of  these  standard  specifications,  with  a  standard  mean  coating
thickness of 140 µm.

Rock dowels/bolts shall be tested in accordance with ASTM D4435

– 08, Standard Test Method for

Rock Bolt Anchor Pull Test, and ASTM D4436

– 08, Standard Test Method for Rock Bolt Long-Term

Load Retention Test.

a. Rock Dowels

Rock dowels shall be passive reinforcement elements that require some ground displacement to be
activated. Similar to passive concrete reinforcement, the effect of dowels is activated by the
movement of the surrounding material. In particular, when displacements along discontinuities occur,
dowels are subject to both shear and tensile stresses. Levels of shear and tensile stresses, and the
ratio between them occurring during a displacement, depend on the properties of the surrounding
ground, the properties of the grout material filling the annular gap between the dowel and the ground,
and the strength and ductility parameters of the dowel itself. Additionally, the degree of dilation during
shear displacement influences the level of stress acting within the dowel.

b. Rock Bolts

Rock bolts shall have a friction or grout anchor in the rock and shall be tensioned as soon as that
anchorage is attained to actively introduce a compressive force into the surrounding ground. This
axial force acts upon the rock mass discontinuities, thus increasing their shear capacity and is
generated by pre-tensioning of the bolt. The system requires a bond length to enable the bolt to be
tensioned. Rock bolts shall be fully bonded to the surrounding ground after tensioning, for long-term
load transfer considerations. They shall be grouted full length. In any case, bolts begin to support or
knit the rock as soon as they are tensioned, that is, the rock does not have time to begin to move
before the bolt becomes effective.

34.3.3.3

Ribs and Lagging

There are still applications where the use of ribs and lagging is appropriate, such as unusual shapes,
intersections, short starter tunnels for TBM, and reaches of tunnel where squeezing or swelling
ground may occur.

Steel ribs may be installed with shotcrete being used instead of wood for the blocking, or lagging,
material. When shotcrete is used, it often does not completely fill the entire void between steel and
rock. Hence, with properly applied shotcrete, it is recommended that the maximum blocking point
spacing be measured at 0.5 m and the design shall proceed according to the Proctor and White
procedure.

34.3.3.4

Shotcrete

Shotcrete is simply concrete sprayed into place through a nozzle. It contains additives to gain
strength quicker and to keep it workable until it is sprayed. Shotcrete can be made with or without
the addition of reinforcing fibres and can be sprayed around and through reinforcing bars or lattice
girders. Both the quality and properties of shotcrete can be equal to those of cast-in-place concrete,
but only if proper care and control of the total placement procedure is maintained throughout.

34.3.3.5

Lattice Girder

Lattice girders shall consist of support members made up of steel reinforcement bars laced together
in a triangular pattern and rolled to match the shape of the opening. Because their area is typically

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small compared to the surrounding shotcrete, lattice girders do not, by themselves, add greatly to
the total support of the opening. However, they do provide the following two significant benefits:

•

They are typically spaced similarly to rock bolts, thus they quickly provide temporary support

to blocks having an immediate tendency to loosen and fall.

•

They provide a ready template for assuring that a sufficient thickness of shotcrete is being

applied.

Generally, lattice girders are used much more frequently in tunnels driven by the SEM.

34.3.3.6

Spiles and Forepoles

Spiles and forepoles shall be used interchangeably to describe support elements consisting of pipes,
pointed  boards,  or  rods  driven  ahead  of  the  steel  sets  or  lattice  girders.  These  elements  (herein
called  spiles)  provide  temporary  overhead  protection  while  excavation  for,  and  installation  of, the
next set or girder is accomplished. Spiles shall be driven in an overlapping arrangement so that there
is never a gap in coverage. Design of spiles is best described as intuitive, as it must be kept flexible
and  constantly  adjusted  in  the  field  as  the  ground  behaviour  is  observed  during  construction.  A
working first approximation of design load might be a height of rock equal to 0.1B to 0.25B, where B
is the width of the opening.

34.3.3.7

Precast Segment Lining

Tunnel lining consisting of precast segments shall be used in single- or double-pass lining systems
to support rock loadings and water pressures. Precast segment lining shall comply with the concrete
durability  parameters  in  Section  21.3.3,  Chapter  21,  Concrete  Structures,  of  these  standard
specifications.  Concrete  segments  shall  be  reinforced  either  with  reinforcement  bars  or  fibre.
Segment rings shall consist of five to seven segments with a key segment. Ring divisions and the
segment dimensions have to be optimised according to the Project-specific requirements that include
tunnel  diameter, maximum  size for  transport  and  installation  or  erector,  and  the  number  of thrust
jacks and their distribution over the range of the ring.

Precast segment concrete lining shall be used in TBM tunnel construction and in soft-ground tunnels.
Segmental rings shall be erected in the TBM tail shield and during the advance, the rams shall act
on the ring. Rings shall never be independent from the TBM, hence the design of the TBM and the
segmental ring must be harmonised. Rams must act on prepared sections of the ring, rolling of the
tunnel shield and the ring must be taken into account. Ram axis shall be identical with the ring axis
and ring tapers shall be designed according to the TBM curve drive capabilities and not only
according to the designed tunnel axis.

34.3.4

Groundwater Control during Excavation

This work shall consist of controlling groundwater in rock that can take many forms, depending on
the nature and extent of the problem. A combination of control methods for the tunnel may be
employed by the Contractor, which may also apply different solutions at different locations along the
alignment.

34.3.4.1

Dewatering at the Tunnel Face

Dewatering at the tunnel face is the most common method of groundwater control. This consists
simply of allowing the water to drain into the tunnel through the face, collecting the water, and taking
it to the rear by channels or by pumping. It then joins the site water disposal system. Consideration
shall be taken by the Contractor that if there are hydraulic or other leaks or spills at the TBM or other
equipment in the tunnel that such contaminants are in this water.

34.3.4.2

Drainage Ahead of Face from Probe Holes

Probe holes may be placed by the Contractor ahead of the tunnel to verify the characteristics of the
rock and to provide information for machine operation and control. These holes shall also pre-drain

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the rock and provide warning of, and drain, any methane; hydrogen sulphide; or any other gas,
petroleum, or contaminant that may be present. In areas where there are such known deposits of
gas or other contaminants, it is recommended to keep one or more probe holes out in front of the
machine. When such materials are encountered, the probes shall alert the workers of the need to
increase the frequency of gas readings, to increase the volume of ventilation, or to take other steps
to avoid the problem of unexpected or excessive gas in the tunnel.

34.3.4.3

Drainage from Pilot Bore or Tunnel

Pilot tunnels shall be constructed by the Contractor as per the Contract documents. These pilot
tunnels shall provide the following benefits to the main tunnel drive:

•

Groundwater drainage;

•

Gas or other contaminant drainage;

•

Exploratory information on the geology;

•

Grouting or bolting galleries for pre-support of a larger opening; and,

•

Rock behaviour and loading information for design of the larger opening.

Pilot tunnels are typically 2 m to 2.5 m in general size, and may be located at one or more of several
locations.

34.3.4.4

Grouting

Groundwater inflow into rock tunnels almost exclusively comes in at joints, bedding planes, shears,
fault  zones,  and  other  fractures.  Because  these  can  be  identified,  grouting  shall  be  the  most
commonly used method for groundwater control. A number of different grout materials shall be used
depending  on  the  size  of  the  opening  and  the  amount  of  the  inflow.  Zones  of  potentially  high
groundwater inflow shall first be detected by the Contractor by drilling probe holes out in front of the
tunnel face. Second, the zones shall be characterised and, hopefully, the major water carrying joints
tentatively defined. Third, a series of grout holes shall be drilled out to intercept those joints 3 m to a
tunnel diameter beyond the tunnel face or wall. Fourth, using tube-a-machetes, cement, or water-
reactive grouts shall be injected to seal off the water to a level such that succeeding holes are drilled
as  the  fifth  step  and  injected  with  finer,  more  penetrating  grouts

— such as micro- or ultra-fine

cements or sodium silicate

— can be injected to complete the sealing process. Based on evaluation

of the grouting success, additional holes and grouting may be required to finally reduce the inflow to
an acceptable level. Steps four and five shall be repeated until the required reduction in flow is
achieved.

34.3.4.5

Freezing

On rare occasions, it may become necessary for the Contractor to try freezing in a tunnel in rock for
groundwater control. This might occur, for example, at a shaft where it is necessary to control the
groundwater locally for a breakout of a TBM into the surrounding rock. If upon beginning excavation
of the TBM launch chamber it is found that the water inflow is too great, the alternative control
methods shall be to grout, as discussed above, or to freeze.

The maximum groundwater velocity for which it is feasible to perform effective freezing shall not
exceed 1.8 m per day. Therefore, freezing shall not be used in rock tunnelling, except locally, and
even then it might be necessary to use liquid nitrogen to perform the freezing.

34.3.4.6

Closed-Face Machine

A closed-face machine may be used by the Contractor for rock tunnelling in high groundwater flow
conditions over short lengths. In reality such a machine shall be similar to an earth pressure balance
(EPB) machine with sufficient rock cutters installed to excavate the rock. For any extended length
measuring greater than a 100 m, this process shall be uneconomical because the machine shall
have to grind up the rock cuttings and mix and the resulting fines with large quantities of conditioners

Abu Dhabi, United Arab Emirates. STANDARD CONSTRUCTION SPECIFICATIONS (PART 2 - ROAD STRUCTURES, 2020) - page 21