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PROJECT REPORT ON TUNNELING IN ARID

ZONES�SAG Refresher Course No. 13201 from 7.1.2013 to 15.2.2013�

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PREPARED BY : A.K. SETHI CE(C) -V, NWR- JAIPUR SAG REFRESHER COURSE 13201�

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CONSTRUCTION METHODOLOGY

CONTENTS

Page No.

1. General 1

2. Introduction 1-4

3. Execution Plan 5

4. Engineering 6

5. Construction 6-37

1.0 GENERAL

North – Western Railwayisconstructing single line BG Standard straight

alignment tunnel in soil and rock including cut & cover portion between

chainage 38/720 to 40/860, including side drains & other protection works on

both approaches of tunnel between Didwana- Lalsot Railway stations in

connection with Dausa – Gangapurcity new BG line project.

2.0 INTRODUCTION

Lalsot Tunnel (Gangapur City- Dausa New Line Project)

A new B. G. of 92.67 km between Gangapur City and Dausastatation of N. W.

railway is under construction. Near Lalsot town, the alignment passes through

Aravali range, where a tunnel is under construction. Total length of tunnel is 2140 m

which includes 786.5 m of cut & cover portion also. As per geo-tech investigation

and bore-logs as well as per actuals, length of tunneling is 1350 m, out of which, 650

m is hard rock and remaining 700 m is in soil and mixed strata.

Detailed geotechnical investigation was carried out to obtain adequate information of

the ground conditions and up to the depth of the tunnel bottom, the type and strength

of sub-soils / Rock and other geotechnical details of relevance to enable arriving at

the design parameters before invitation of tender. The Investigation comprises

drilling boreholes, carrying out Electrical Resistivity test, Chemical Test etc. Soils of

Lalsot area are greyish brown to Red brown and yellowish brown with wide

variations intexture from sandy loam to clay loam.

The soil strata changes at later depth to boulders of Quartzite at some point. Rocks

are present at the mountain and near the base of mountain, initially boulder mixed

soil and later rocks which are Metamorphic type. There is difference in ground level

between North and South side of mountain range at Lalsot. The ground at

North of ridge ( towards Dausa ) is higher by 55 m in comparison to ground towards

South of ridge. Because of huge difference in ground levels, the alignment is

continuously in cutting in 4 km length before start of tunnel with 1 in 150 downward

grade towards Lalsot. The depth of cutting at the start of cut & cover is 18 m while

the same is 29 m at the North face. The grade inside the tunnel is 1 in 150, one sided

towards South. The height of embankment at the South face of tunnel is 14 m.

Methodology Adopted For Tunneling

As per geo-tech report, the strata in cut & cover portion from ch. 38/720 to 39/520

are made of yellow brown silty sand mixed with clay, brown Clayey Silty Sand with

kankar and gravel up to formation level. No water table was encountered during bore

logging and but at the time of execution in rainy season water bearing strata in some

stretches is encountered of both end face of tunnel. The strata from ch. 39/520 to

40/311 are made of silty sand, Red Brown Clayey Silty Sand with Kankars and

gravels, sand mixed with boulders. From ch 40/311 to 40/860 strata consists of hard

rock of metamorphic origin.

At North face tunneling was taken up by heading method to be followed by

benching. Strata encountered during excavation were predominantly silty sand, silty

clayey sand mixed with kankar and gravel, in conformity to bore log details.

Excavation in heading was taken up with the help of EX 70 and 2.0 m of tunnel face

being excavated at a time. After putting the wall plate of 2.0 m, 4 steel ribs fabricated

of ISMB 200X100 are erected subsequently followed by placing of R.C.C. A

progress of 2.0 m in heading was being achieved in cycle time of 16-18 hrs. After 60

m progress in heading, benching was taken up with the help of Ex 70 excavator and

soon after bottom concreting was done after putting bottom strut in position. The

progess simultaneously 225 m progress of full face achieved so far at DO end face of

tunnel and further heading has been progressed 255 m.

Initially tunnel on south face was started with heading and benching method. As

strata were highly jointed having patches of weathered rock, permanent steel

supports, made of ISMB 150X75 in arch ribs and columns at 1 m centre tocentre,

erected initially in 80 m length of tunnel. With improvement in rock quality and

joints, steel support was discontinued and unlined profile was adopted. The decision

was taken that 80 m – 136 m length should be lining concrete without support and

136 m -186 m lining concrete with support and further 186m - 530 m lining concrete

without support and 530 m-630 m and onwards uptosoftrocks lining concrete with

support are proposed.

The purpose of constructing D-Shape Tunnel is to cross through the Hill by the

railway line. The scope of work for underground construction of Tunnel by

conventional method includes, but is not limited to the following:

• Preconstruction works consisting of all necessary platforms and

accesses, roads, storage areas, parking areas, air compressors,

fabrication yards, batching and mixing plants, fuel dispensing unit,

operation facilities, workshops, warehouses, storage for explosives,

storage of pumped out water, sanitary and sewage disposal systems,

surface drainage system, medical facilities, offices, camp facilities,

construction water, construction power, utilities etc.are required to

complete the TUNNEL WORK.

• Construction of approach roads to tunnel faces from the existing road

and from site to disposal areas, suitable for movement of vehicles.

• Mobilization and demobilization of personnel and equipment for

underground construction, including that for drilling, blasting, scaling,

mucking, hauling, rock support, concreting, grouting, dewatering,

ventilation, illumination and surveying.

• Supply of all materials required for drilling, blasting, rock support,

concreting and grouting.

• Suitability trials if required for shotcrete, rock bolts, anchors and

grouting.

• Surveys, alignment and measurement.

• Portals construction.

• Stabilization of slopes at portal if required.

• Underground excavation by the drill and blast method, including

ventilation, scaling, mucking, hauling and disposal of muck at

designated disposal areas.

• Geological mapping of each face by an experienced engineering

geologist.

• Installation of temporary rock support if required.

• Installation of permanent rock support if required.

• Installation of rock support for unexpected geological conditions if

required.

• Installation and operation of de-watering system if required.

• Probe drilling to asses’ geological conditions ahead of the face if

required.

• Contact grouting if required.

• Excavation for pump pits.

• Disposal of seepage water.

• Excavation of underground niches if required for construction purpose.

• Underground shotcrete, rock bolts; concrete worksetc. if required for

stabilizing the roof.

• Cleaning of all the underground works after completion of the job ETC.

3.0 EXECUTION PLAN

Immediately after mobilization of required machineries to the site, the job of

excavation of approach cut at exit end and construction adit at the junction of

cut & cover and Tunnel shall complete first.After completion of the approach

excavation or portal excavation and slope stabilization, the contractor shall

take-ups the construction of Portal at both the ends of the tunnel.

Once the portal construction and its stabilization is over, the contractor shall

take-up the excavation of the Tunnel by drilling and blasting or any other

suitable methods demands by the strata available at site. Details of execution

procedure, planning to adopt by the contractor shall be collected before start of

the underground excavation work. The major items to be executed in this

project are listed below:

a) Approach cutting

b) Establishing of portals

c) Construction of cut & cover

d) Slope stabilization at the portals

e) Under ground excavation for tunnel in rock and soil

f) Rock bolting for roof and side wall support

g) Shotcreting for roof and side wall support

h) Steel supports erection

i) Portal RCC lining

j) Concrete lining

k) Pressure and contact grouting

l) Base concrete if any etc.

4.0 ENGINEERING

As per the geological report made available, the entire stretch from Km.

38/720 to 40/860 can be divided into three category of tunneling based on the

execution procedure, they are cut and cover tunnels, tunnels in soft strata and

tunnels in rock strata.

The total length of the stretch is approximately 2140m, including cut & cover,

tunnel in soft strata and tunnel in rock. Due to the cut & cover and tunnel in

soft strata it is necessary to establish a construction adit or shaft at the junction

of cut & cover and soft strata to provide more working faces to complete the

work in the schedule period. Hence it is advisable to provide an adit at the

junction point and construct a shaft as a natural ventilation purpose.

5.0 CONSTRUCTION

A. SEQUENCE OF EXCAVATION FOR TUNNEL

After completion of the approach excavation and establishing of portals,

excavation of the Tunnel is carried out from both the faces (Entrance and exit)

simultaneously by full face or heading and beaching method depending upon the

strata available at site.

A.1. GENERAL PROCEDURE OF UNDERGROUND EXCAVATION

Tunnels can be driven through almost any material in nature, but the methods

used and costs differ radically. Thus, the method used in tunneling in earth, soft

sediments or crushed weathered rock depends chiefly on the bridge action period

of the material above the roof of the tunnel and the position of water-table,

whereas the method used for tunneling through hard , intact rock requiring little or

no supports depends upon the strength and condition of rock, because of great

longitudinal extent of the work many different kinds of conditions are

encountered which for maximum economy should be excavated and supported

differently.

Preliminary works

The preliminary works required to commence the excavation of a tunnel consists

of the following:

i) Precision survey and setting out of the tunnel alignment.

ii) Open excavation for portal or excavation for shaft.

iii) Arrangement for collection of surface water and its drainage by gravity

flow or pumping.

iv) Access roads or rail tracks to mucking areas.

v) Erecting or winching and hauling equipments.

vi) Establishment of field workshop, compressors and air lines, pumps, water

lines, ventilations fans and ducts, lighting, concreting arrangements,

supports erection arrangements, etc.

Precision survey

The precision survey and setting out of the tunnel alignment shall consist of

transferring the obligatory points like portal points, shaft location, etc from

topographical maps / detailed design drawings to the actual site of

construction. This is done either by “Direct Setting Out” or by

“Triangulation”. In the mountainous regions it is an extremely rare possibility

that both the ends of the tunnel will be visible from each other and hence

“Triangulation” has to be invariably adopted for setting out the alignment. The

levels of the various portals along the tunnel are then fixed accurately by

means of Total Station or using “Reciprocal Levelling”.

Location of Portals

A tunnel portal is the face from where a tunnel starts. Its location is decided

with reference to the design, vertical and lateral rock cover actually getting at

site. The minimum cover with which tunnel can be started depends upon the

type and structure of rock, size and shape of tunnel and the internal water

pressure.

Methods of Underground excavation

The underground excavation for tunnels shall be carried out in conformity with

IS: 5878 Part II /Section-1 or other relevant references mentioned as per the

tender documents. Tunneling in soft strata shall conform to IS: 5878 part-III or

other relevant references mentioned as per the tender documents. The actual

operations for underground excavations may vary with the type and size of

tunnel, method of excavation, type of geological formation encountered,

equipment available, and the overall economics. Following are the methods

commonly adopted.

Full Face Attack

In this method, the entire cross-section area of the tunnel to be excavated is

attacked simultaneously. This method is generally recommended for small size

tunnels and tunnels in good rock conditions where major rock falls are not

anticipated.

FULL FACE IN GOOD ROCK WITH DRILLING BOOMER

Top Heading and Benching

Where the tunnel has a very large cross-sectional area or where the rock is not

of good quality or soil, the top heading and benching method is generally

recommended. In this method, a top heading is excavated first-either to full

length or part length of the tunnel, and is supported simultaneously. The

benching is then removed slowly.

TOP HEADING AND BENCHING IN LOOSE STRATA

Bottom Heading and Stopping

Where the rock is consistent and sound and the tunnel section is very large,

this method can be easily adopted. In this method a bottom heading is made

first and the overhead stope is removed later.

Drift Method

In driving large tunnel it may be economical to drive a small tunnel called a

drift or a pilot tunnel prior to excavating the full face. Depending upon the

nature of rock and other parameters, a drift may be excavated in the centre,

side bottom or top.

Steps involved in underground excavation

The actual steps involved in boring the tunnel depend upon the mode of tunnel

boring. The most commonly adopted method of tunnel boring in India is the

“conventional drilling and blasting method”. The other methods used are

a) Cut and cover methods; in long, prefabricated sections snuck in place as

in immersed tubes; in short prefabricated sections pushed into place from

jacking pits.

b) Mechanized means such as Tunnel Boring Machines (TBM) or

continuous miners (road headers).

c) Tunneling with the aid of a protective shield in free or compressed air,

and they will eventually be constructed in ways now existing only in our

imaginations.

In NW Railway tunnel at Jaipur, it is better to execute tunneling by

‘conventional drilling and blasting method’ as per the availability of rock

strata. In the soil strata the excavation shall be performed by the help of

excavators. For an underground exaction driven in rock by conventional

drilling and blasting, following operations shall be normally followed:

• Marking the tunnel profile,

• Setting up and drilling holes,

• Loading explosives and blasting,

• Defuming or removal of foul gases by ventilation,

• Checking for misfires,

• Scaling the loose material,

• Removal of Muck (Mucking),

• Installation of rock support system as necessary for safety and quality of

the underground structure.

SCHEMATIC DIAGRAM SHOWING SEQUENCE OF OPERATION

IN TUNNEL EXCAVATION

Marking the Tunnel profile

The centre of the tunnel and its level is marked on the face of the tunnel with

the help of precision survey instruments before each blast and from that centre

line point the designed shape of the tunnel (profile) is marked on the face. The

maximum deviation of the tunnel axis relative to the prescribed theoretical axis

shall not exceed 5cm. Fixing the centre line and marking the profile in each

blast is the very important function for reducing the over breaks and wastage

of materials.

Setting up and drilling holes

Blast Pattern

The Blast Patterns shall include the following:

- drill pattern (geometrical data) with holes coordinates regard to the center of

crown’s line, indication of blast holes spacing, diameter of the holes, planed

drill length of the blast and excavated solid volume

- charging pattern, with detailed charge by kind of hole: cut holes, peripheral

holes, extracting holes. This part will include the type of explosive, the total

quantity of explosive for the blast, and the indicative ratio W / V (explosive

weight / excavated solid cubic meter)

- priming pattern with kind of trimming (electrical non-electrical, etc.), type

sequence and number of delays, delays pattern, diagram for blast, size and type

of hook-up lines and lead lines and type and capacity of blast initiation device.

The priming pattern shall indicate the maximum instant unitary load

(maximum load blasting at a defined time)

The blast pattern shall be adapted to actual rock conditions encountered during

excavation works.

Designing the Blast

An important step for blasters is designing the blast. Blasters design blasts that

will produce desired rock fragmentation results and low vibration levels. They

specify explosive quantities and design borehole drill patterns including size,

depth, and spacing. These factors vary based on the geology and location of the

blast site. Different rock types require different kinds or amounts of explosives

and different borehole spacing. Blasts are also designed to produce desired

fragmentation, or rock size.

Trial Blast

Trial blasting will be performed at the beginning of the works in order to optimize

blast design and drilling patterns. The purposed of this trial blasts is as follows:

• Estimation of blast design parameters suitable to the site

• Suitability evaluation of the approved blast design

• Checking the blast vibration level

The trial blasting shall be performed in the presence of NW RAILWAY

representative and blast engineer of the company in order to guarantee the

reliability of trial. Blast vibration can be assessed based on the result analysis

for the trial blast, and then suitability of approved blast design can be

evaluated. Drilling length, diameter and spacing of hole, and burden length

shall be adapted based on the allowable amount of explosives per delay in line

with the efficiency of drilling equipments.

Holes are drilled by using pusher leg and jack hammer manually. The pattern

of drilling and the number of drill holes is governed by the strength of rock,

size and shape of tunnel, strength of explosives and the fragmentation of rock

required so as to make it suitable for mucking. Diameter of the drill hole may

be kept 4mm more than the diameter of the explosive cartridge.

The following holes shall be drilled in the face of a tunnel to achieve

excavation:

Cut holes: These holes shall be drilled in the centre of cross section of the

tunnel to excavated converging towards the centre of the face to produce an

initial cone or wedge. The holes shall be 150mm to 300mm deeper than other

holes.

Easer holes: These holes shall be drilled to blast the area around the

cone/wedge created by the cut holes and there by reducing the burden on other

holes. Charge in these holes shall be less than that in cut holes. Easer holes

shall be drilled around the cut holes.

Trimmer or contour holes: These holes shall be drilled along the periphery

of the tunnel to give the excavated section a required shape. These holes shall

carry relatively less charge to reduce over breaks.

Loading explosives and blasting

Explosives used in blasting are generally made of Gelatine in varying

percentage depending upon the strength of rock to be blasted. Before loading

is started, each hole is blown out with a high pressure air jet to remove loose

cuttings and water. The explosive, which is available in the form of cartridges

ranging from 25mm to 63mm in diameter and 200mm to 300mm in length is

then inserted in the hole and tamped well into the bottom with the help of a

wooden /plastic pole. A primer cartridge containing the detonator pointing

towards the bottom of the hole and tamped lightly to prevent jarring of the

detonator. The remaining cartridges are then lowered into the hole and then

tamped firmly in place taking care to prevent breaking of detonator lead wires.

Finally, the remainder of the hole not occupied by explosives (each holes

required to carry only the designed weight of explosives) is filled with an inert

material (like a damp mixture of clay and sand) and tightly tamped. The holes

are then blasted from a safe distance. In LalsotNW RAILWAY Tunnel project

Gelatine sticks shall be used. Adequate safety precautions shall be taken

during drilling and blasting operations in conformity with IS: 4081 and other

relevant guidelines.The actual drill pattern shall be arrived after the field trials.

Tunnel Ventilation

Ventilation is an important aspect, which has to be duly taken care of for

efficient underground excavation of the Tunnel. Adequate ventilation in tunnel

shall be provided to make the working space safe for workers, by keeping the

air fresh and breathable, free from harmful obnoxious gases and dust.

Ventilation also serves the purposes of bringing down high temperatures

(especially at the working face) due to diesel engines working inside the

tunnel. Minimum requirements of purity of air, dust control and volume of air

shall be in accordance with IS: 4756 and other relevant guidelines as per the

tender provisions.

The tunnel shall be ventilated either by blowing air in or exhausting it out

through a duct. In the blowing mode, fresh air from the surface is forced

through the vent line to a point near the face. The exhaust air travels back

through the full length of the tunnel to the portal of access tunnel or shafts.

This mode has the advantage of constantly supplying fresh air to the face

where most of the work is done. It has the disadvantage of exposing the

remainder of the tunnel to any contaminated air generated at the face.

In the exhaust mode, the foul air is exhausted through the vent line, and the

fresh air enters at the portal or shaft and travels through the tunnel to the face.

While this method creates a better environment along the tunnel, any heat,

moisture, dust, and smoke generated along the tunnel is delivered to the

vicinity of the face.

A TYPICAL TUNNEL VENTILATION ARRANGEMENT & ALSO SHOWS

THE FIXED ROCK BOLTS AND SHOTCRETE IN APPROACH CUTTING

Checking Misfires

Immediately after the tunnel has been defumed and ventilated, the blasted face is

checked carefully for any misfires. For this an experienced and competent Forman

enters the tunnel, removes the loose rock carefully from the face and makes sure

that all cartridges have been fired.

Scaling the loose material

After the checking of misfire is over, the scaling operation will be carried out by

use of excavators with hydraulic hammer attachment. Manual scaling as shown in

the schematic diagram may not be advisable or practical in safety point of view.

Removal of Muck

The material removed as a result of blasting is loaded into tippers, dumpers or

mine cars, as the case may, and is taken out of the tunnel. In principle, tire or

crawler mounted loaders/excavators and suitable dumpers are used for mucking

operation. Removal of muck from underground excavations shall be in

conformity with IS: 5878 Part-II/Section-2 and other tender provisions. The

excavated materials (rock, soil etc) from the tunnel shall be transported to the

specified dumping area. A haul road shall be constructed at the hill side of the

dumping area on the higher elevation. The excavated material shall be dumped

from the higher elevation on the hill slope. The same shall be levelled using

suitable dozing equipment.

A2.Tunnel Portals

As a normal practice whenever tunnel operation is to be started, a portal has to be

constructed at the working face. Thus, it is obvious that an approach road has first

to be constructed to reach the working face. It has been seen generally that rocks

near the working face are highly weathered and the first few meters are nothing

but loose overburden. This loose overburden is first of all removed and thus a

working platform at the invert level of the proposed tunnel is made available. The

outline of the tunnel face is then marked on the exposed rock face and an RCC or

steel framed portal is constructed around the periphery of the proposed tunnel.

The main function of the portal is to provide a well defined access to the tunnel

and to protect the tunnel face from loose over burden falling above the tunnel

opening. This tunnel will have only two portals, one at entry side and another at

exit side.

A3. ROCK SUPPORT

When an underground opening is made, it generally becomes necessary to install

supports to hold the rock which has a tendency to drop out of the roof of the

opening. With the increased availability of steel sections, the emphasis was

shifted to these sections as they were found to be stronger, longer lasting and ideal

for tunnel supporting in almost all types of situations. However, as more and more

tunnels were excavated and more data became available to the engineers world

over, new methods of tunnel supporting were evolved. The feeling now is that any

opening can be self supporting permanently if the rock around it is suitably

reinforced so that the reinforced rock becomes a competent structural entity. The

new means of rock reinforcement are the rock bolts and shotcrete.

The usual support methods are a combination of permanent steel supports, rock

bolting, shotcrete / fibercrete wiremesh etc. The types of rock supports

recommended in this project are rock bolts, steel ribs & back fill concrete and

shotcrete.

a) Permanent Tunnel Supports

Permanent tunnel supports shall be provided wherever the tunnel strata are poor.

The size of steel support will be as per the detailed design and as per the site

conditions. A typical permanent tunnel support is shown below.

Typical Permanent Tunnel Supports

b) Rock bolts

Rock bolt is the general term that includes rock dowels and cable tendons.

Specifically, bolts are pretensioned, while dowels are initially unstressed.

Originally, the prestress was considered, necessary to increase the internal friction

in the rock mass. However, it was soon realized that any movement in the mass

would stress the untentioned dowel as well as be inhabited by the dowel. As a

result, the economy and simplicity of the dowels reduced the use of bolts to

special situations, such as very narrow pillars where the additional confinement

provided by the pretension force is considered necessary. The use of tendons is

limited to long distances between anchorage and excavated surface.

It is necessary to fill the gap between bolt and drill hole to avoid the possibility of

corrosion if the bolt is to be considered permanent and a part of permanent

support.

The search for economical installation procedures resulted in the development of

epoxy resign cartridges to eliminate both the anchorage hardware and the extra

grouting process. The cartridges have an internal membrane separating the two

components. When the components are mixed, they harden in well-defined time

increments. This permits use with either dowels or bolts. The installation process

is simple: drill the hole; insert the requisite number of cartridges; insert the steel

bar with a spinning action and continue spinning for about 60 seconds to ensure

complete mixing. Setting of mixed material occurs shortly thereafter. It should be

noted that after years of usage, the long-term performance of the resign has been

called into question; as a result there is movement towards returning to cement

grouting.

As a safety measure immediately after the scaling operation, systematic rock

bolting shall be carried out as per the requirement/site condition and detailed

designs.

Typical Details of Rock Bolt

In these tunnels the rock bolts considered most appropriate are reinforcing steel

bars, typically 20 mm diameter, 12 tons proven capacity. When spot bolting is

required the geologist or geological engineer in conjunction with the supervisor or

engineer responsible for the face decides upon the location of the bolts. The

decision may be taken that systematic bolting is required for a particular section.

In this case, some bolt locations may be moved from their exact grid location to

better take account of local rock features (it would be senseless and useless to drill

a hole entirely along and/or within an existing joint). For 20 mm passive bolts,

holes of 28 mm to 38 mm are required. The hole is filled from the bottom with

cement capsules and resigns capsules and the bolt is inserted as per the railway

designs. Care must be taken to ensure that the hole is filled to the full depth. The

bolts are threaded at outer end. When the grout has set, a washer plate is placed

against the rock and secured in position with a nut. When shotcrete is used, the

washer should be outside the main layer of shotcrete. The exposed washers and

bolts should finally be covered with a protective layer of shotcrete to prevent

contact with the product and from corrosion.

c) Shotcrete

Shotcrete is not just “pneumatically applied concrete”. Although the basic

materials (cement, aggregates, water) are the same and meet the same Indian

Standards, additives (e.g.: accelerators, micro silica, and steel fibers) change its

character to make shotcrete unique and usable in quite a different fashion than

concrete.

Early on, all shotcrete was dry mix, Nozzles did not provide adequate mixing of

solids and water, and remote control operation was nonexistent. There are definite

differences between, and advantages of, the wet-mix and dry-mix concretes, even

though the end products can be nearly identical. In this project we shall adopt the

wet mix procedure.

The wet-mix process consists of mixing measured quantities of aggregate,

cement, and water, and introducing the resulting mix into a vessel for discharge

pneumatically or mechanically through a hose to final delivery from a nozzle. It

has the advantage of rigidly controlling the water/cement ratio of the product.

Existing equipment can handle maximum aggregate size of ¾ inches. Further,

successful methods have been devised to introduce quick-acting accelerators to

the delivery hose.

Surface Preparation

Good adhesion to the ground with the initial layer and good bond between

successive layers are prerequisites of good shotcrete. The surface to be shot must

be clean and moist, but not, wet, immediately before shooting. This can best be

accomplished with a high-pressure combination air-water jet applied with a long

jet-pipe nozzle held relatively close to the surface. Merely washing the surface

with water applied through the shotcrete nozzle is insufficient. Similar cleaning is

necessary when a considerable time has elapsed between applications or when

work in the heading has resulted in deposits on the shot surface.

Dry-Mix Aggregate Preparation

When dry-mix aggregate storage is on-site, protection from the elements (rain etc)

is necessary. Stockpiling by size groups should prevent sub size segregation. For

best result, an aggregate dampness of 3 to 6% should be maintained. Less will

absorb too much mix water; more will result in too high W/C ratio.

The Mix

The mix design shall be made as per the IS standards. The mixing of materials

shall be done using a 30 cum batching plant (or from a ready mix plant). Inclusion

of steel fibres will require little or no change from the plain shotcrete mix. The

principle effect will be a some what harsher mix with less slump. However with

micro silica the workability will be increased. Over all, the mix design should

keep water cement ratio and the cement factor as low as possible and the coarse

aggregate fraction as large as practicable.

Nozzle

The best shotcrete “ on the wall” is produced when the nozzle is kept with in 3 to

5 feet of the surface being shot and perpendicular to the surface or with in 15

degrees of the same. Deviation from this will result in less compaction (density)

and more rebound. Considering the particles in shotcrete stream are travelling at

170 to 340 mph, it is easy to understand why nozzle man, even when wearing

protective clothing and equipment, are rarely found manually holding the nozzle

in proper position. In order to overcome these problems a remotely controlled

nozzle at the end of a long boom has been adopted in this project.

Curing

Curing of the shotcrete shall be taken up by spraying water jet on the surface.

Testing

Testing is required of the raw materials, the operator, and the field applicability

and of the shotcrete product at various stages of mix development.

Wet shotcrete of required thickness as per designed thickness shall be provided

wherever required in the crown portion and walls of the tunnels and Tunnels.

When a new round has been blasted, the person responsible for progress at the

face examines the rock before mucking is undertaken. Rock support is decided

based on the geological mapping and after scaling. This is jointly undertaken with

the geologist and supervisor; the owner's representative may also be present at this

time. The initial design provided forms the basis for the decision making process.

The behavior of the tunnel section is monitored, by measurement or observation,

at certain intervals and in particular locations and the base case design for

different rock classes is modified as the excavation progresses.

d) Backfill concrete

As mentioned above on tunnel supports and tunnel lining respectively, the job of

tunnel support or tunnel lining does not end with the installation of a support

system (steel ribs, rock bolts, shotcrete, etc.) and provision of lining (PCC, RCC

or steel). For arresting the further displacements and movement of the strata

around an excavated and supported underground opening it becomes absolutely

necessary to backfill the space between the support system and the excavated

surface. The back filling is done by means of placing tightly packed M20 concrete

behind the supports. Experience shows that there are always certain interstices

left in the concrete and also between the concrete and the excavated rock surface.

In order to fill up these interstices and also to provide a proper bond between the

concrete and the rock surface, grouting is to be carried out.

e) Grouting

In order to ensure complete contact of the concrete lining and the rock behind it,

contact grouting with cement grout will be done after the lining concrete has

matured for at least twenty one (21) days.

Grouting in tunnels is of two types:

i) Back fill or contact grouting

ii) Pressure grouting or consolidation grouting

Contact Grouting

The main purpose of the contact grouting is that it fills up all voids and

cavities between the concrete lining and the rock. Contact grouting also

known as low pressure grouting or backfill grouting. Backfill grouting

shall be done at a pressure not exceeding 5 kg/cm2 and shall be

considered as a part of concreting. The normal range of pressure varies

from 2kg/cm2 to 5kg/cm2. It shall be done throughout the length of the

concrete lining not earlier than 21 days after placement after the concrete

in the lining has cooled off.

Pressure Grouting or Consolidation Grouting

In the conventional drilling and blasting method of tunnel excavation, the

rock around the cavity gets shattered to a certain depth depending upon

the depth of blast holes and the type of rock. The aim of consolidation

grouting, as the name suggests, is to consolidate the shattered rock by

filling up the joints and discontinuities in the rock which got opened out

during blasting operations. As a result of pressure grouting, the rock

quality gets improved thus increasing the resistance of the rock to carry

internal water pressure. The consolidation grouting is done after the

backfill grouting is completed in a length of at least 60m ahead of the

point of grouting. Pressure grouting shall be done all around the cavity

and for a uniform radial distance equal to at least 0.75 times the finished

diameter of Tunnel from the finished concrete face. The normal range of

pressure grouting shall be 7 to 10 kg/cm2.

The process of grouting consists of the following operations:

a. Drilling holes

b. Cleaning and washing holes

c. Testing holes

d. Grouting holes

e. Testing of grouted zone for efficacy of grouting.

Drilling of holes

The rings of grout holes may be spaced at about 3m centre to centre. Each

ring may consist of three to four grout holes. It is recommended that

drilling through the lining should be avoided to the maximum possible

extent. This is feasible by placing GI pipes in position while concreting.

This would ensure that the holes are located as per the design and no

unnecessary damage is done to the concrete lining. The normal size of

grout holes is kept 40mm and the size of GI pipes placed in the concrete

lining shall be 50mm internal diameter.

It is desirable that a drill hole is grouted before drilling the adjoining holes

so as to avoid the blocking of holes by the flow of grout if the adjoining

holes are interconnected. In all types of grouting, it is mandatory that the

side holes are drilled and grouted first before drilling and grouting the

crown holes.

Cleaning and Washing Holes

The holes after being drilled to the desired depth shall be cleaned by

blowing air through compressors and then washed by flushing water

under pressure.

Testing holes

The holes are tested for water intake to ascertain the efficacy of the

grouted holes later on.

Grouting holes

Grouting is done by injecting the grout mixtures through grout pumps into

the grout holes. In the semi automatic type of grouting pumps where the

control of grouting pressure is done manually, or return line equipped

with a pressure relief valve must be provided on the manifold as a

precautionary measure against the application of excessive grout

pressures.

Once the grouting of a hole is commenced it should be continued without

interruption until completion. In general, grouting should be considered

complete when the intake of grout at the desired limiting pressure is less

than 2 litres per minute average over a period of 10 minutes for pressures

more than 3.5 kg/cm2 and one litreper minute for pressures lower than 3.5

kg/cm2.

After the completion of grouting operation, the holes should be closed by

means of a valve to maintain the grout pressure for a sufficient period to

prevent the escape of the grout due to back pressure and flow reversal.

The period of closing may range from one to two hours depending upon

the type of strata and the consistency of grout.

Testing for Efficacy of Grouting

This testing shall be done by drilling holes in between the two successive

grouted sections and by performing water intake test in these holes and

comparing it with the results of the test conducted prior to grouting. If the

water intake has not comedown sufficiently, further grouting may be

considered necessary by increasing the number of grouting planes.

Type of grouting equipment shall be decided in consultation with NW RAILWAY.

Maintenance and Upkeep of Grouting Equipment

After each days job the grout pump, the inlet manifold, the delivery pipe, the

return pipe and various valves and fittings should be thoroughly cleaned with

water. The nozzles of manifold, pipes and valves etc. should be preferably oiled

or greased to prevent any sticking of cement mixture.

f) Tunnel Lining

The lining of the Tunnel will be taken up when the excavation of the tunnel, has

been completed. Keeping in view that six faces are available for concreting it is

proposed to use six conventionally designed shutters for lining of Tunnel to

complete the lining as per the Construction Schedule. The shutter will be 6.5

metre long which will enable the concrete lining of whole section of six metre

length in one go. These shutters will give an average lining progress of one

hundred (100) metre per/month/shutter. In the sections where lining in complete

section is to be provided specially designed shutter for overt shall be erected and

concreting of overt shall be done with this overt shutter. These shutters will be

deployed from inlet and exit ends.

The placement of concrete behind the shutter shall be accomplished by a concrete

pump – of 30 Cum capacity or equivalent. The concrete to the Concrete Pump

will be supplied by Transit Mixers. The concrete shall be produced by 30 cum/hr

capacity Concrete Batch Plant (CBP) installed at the entrance of the tunnel.

g) Ground water drainage holes

As per IS: 4880 (Part V)-1972 drainage holes may often provided in other than

water conveying tunnels to relieve external pressure, if any, caused by seepage

along the outside of the tunnel lining. It is recommended that drainage holes may

be spaced at 3m centres, at intermediate locations between the grout rings. At

successive sections, one vertical hole may be drilled near the crown alternating

with two drilled horizontal holes, one in each side wall. Drainage holes shall

extend to a minimum of 15cm beyond the back of the lining or grouted zone.

A4. EMERGENCY RESPONSE

A relevant person shall ensure that, in the event of an emergency at a project,

arrangements have been made for:

(a) the safe and rapid evacuation of people from the workplace; and

(b) emergency communications; and

(c) appropriate medical treatment of injured people.

Details of any evacuation arrangements shall be kept on display in an appropriate

location(s) at the workplace. Emergency escape routes are different for different

locations of the underground works. All such applicable escape routes valid for

particular stretch/location shall be identified and kept for display at that location.

Before completing the tunnel, all the emergency escape shall be through the

working face of tunnel. This will also include the instructions as how to manage

/operate rescue equipment/facilities etc.

Types of emergencies considered should include:

• treatment and evacuation of a seriously injured person;

• fire underground;

• sudden flooding (e.g. inrush from an underground water feature);

• underground explosion (e.g. methane ignition);

• tunnel collapse, resulting in people being trapped;

• power failure; and

• above ground emergency that compromises tunnel safety (e.g. fire or chemical

spill).

The following emergency response control measures shall be implemented:

• providing a system to identify who is underground (e.g. a tag board);

• developing site emergency procedures appropriate for the level of risk,

including establishing an emergency assembly area and a plan for contacting,

and subsequently interacting with emergency services;

• providing emergency response equipment and training in how to use it;

• providing control measures to reduce the severity of the emergency (e.g. self-

closing bulkheads to control water inrush, not required in this tunnel);

• providing fire suppression on vehicles; and

• Providing self rescuers, breathing apparatus and sealable, self-contained

atmosphere refuges as well as instruction and practice in how to use the

equipment.

Risk assessments determine if special emergency provisions, such as emergency

rescue cages and means to extract people from difficult locations (e.g. from the base

of a shaft or heading of a tunnel), are needed.

Traffic management rules should be implemented to ensure vehicles and mobile plant

park in a way that prevents potential runaway and enables clear access at all times.

A close working relationship with local emergency services should be encouraged.

For example, ask the emergency services to visit the tunnel site for site layout, access

and emergency procedures.

Note: Special consideration shall be given to the safe transport of injured people.

Full face supports in soil portion

tunnel

Cross Section of rock portion in hill

Typical Cross section of tunnel

FULL FACE WITH SUPPORT IN ROCK(GGC END)