CONSTRUCTION METHODOLOGY - APSPCB EIA corrected finally/EMP...Environmental Management Plan –...

Environmental Management Plan – Construction Methodology

Hirong H.E. Project, Arunachal Pradesh 16-1

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16 CONSTRUCTION METHODOLOGY

16.1 INTRODUCTION

Hirong Hydro Electric Project is located on river Siyom in West Siang district of

Arunachal Pradesh. The Project envisages construction of a concrete gravity dam 133.5 m high, a

9.2 km long Head Race Tunnel, a 15 m diameter Surge Shaft, two underground pressure shaft

bifurcating into four near an underground Powerhouse to generate 500 MW. Considering the

seasonal variation, the working season of seven months starting from mid October to mid May

every year has been considered while preparing the construction programme especially for the

project works in the open. Underground works have, however, been considered as continuous

even during the monsoon season though with a slow rate of progress on account of practical

problems in movement of heavy machinery and vehicles carrying men and material. Construction

Programme and selection of methodology with the planning for equipment has, as such, been

worked out keeping above site constraints in view. The project has been planned to be

commissioned in a period of six and half years (78 months) including period for completion of

infrastructure development works.

16.2 COMMON EQUIPMENT

For construction of this project, main common equipments are Aggregate Processing

Plant, Batching Plant and Concrete cooling arrangement. These are common for all civil works.

In addition to this, diesel captive power is also amongst common facility. However, this has been

dealt with in Infrastructure chapter because diesel generating capacity is designed not only for

civil works but also for garage and workshops etc.

16.2.1 Aggregate Processing Plant (APP)

Important aspects related to setting up of an APP inter-alia include the following:

i). Capacity and production schedule of aggregates;

ii) Location of plant;

iii) Type of Plants;

iv) Location of quarry areas and method of extraction of river bed materials (RBM) or

quarrying rock, as the case may be.



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The total quantity of concrete to be placed is estimated to be approximately 11.39 Lac

cubic meters for Dam and Intake, 12150 cubic meter in Sitten Nallah, 1.56 Lac cubic meters for

HRT, 34763 cubic meter for Diversion Tunnel and Coffer Dams and 79274 cubic meters for

Powerhouse. For construction of this project, Aggregate Processing Plants (APP) are proposed at

three locations and Concrete Batching Plants (CBP) at six locations. From location 1 of APP

(APP-1) at dam site, aggregate shall be supplied for concreting of Dam, Sitten Nallah and Intake.

From Second location (APP-2) at Powerhouse site near MAT portal, aggregate shall be supplied

for concreting of the lining of part of HRT, Surge Shaft and Powerhouse Complex. From 3rd

location (APP-3) near diversion tunnel portal, aggregate shall be supplied for concreting of

Diversion Tunnel and concrete lining of part of HRT.

As worked out above the APP having capacities of 500 TPH on left bank located at dam

site, 100 TPH APP will be located at Powerhouse site near MAT portal and 60 TPH APP will be

located near Diversion Tunnel portal.

• FE Loader 3 cum : 5 (2 at Quarry + 3 at APP)

• Dozer (180 HP) : 5 (2 at Quarry + 3 at APP)

• Crawler drill IRCM 341 : 2 (at Quarry)

• Compressor @ 450 cfm : 2 (at Quarry)

• 20 tonne capacity dumper : 14 (6 at Quarry + 8 at APPs)

16.2.1.1 Batching Plant

Important aspects related to setting up of an Batching Plant inter-alia include the

following:

i). Capacity and production schedule of aggregates;

ii). Location of plant;

iii). Type and layout

The maximum concreting in a month for all structures as per the construction program is

86,576 cum for Location-1 and 16,000 cum for Location-2 and 10,000 cum for Location-3. The

maximum concrete requirement per month for Location-1 is 82660cum. Also about 10,000 cum

per month concrete is required for Location-3.

Three CBP’s (CBP1, CBP2, CBP3) and CBP6 will be required to match with the APP-1

and APP3. For APP-1 works, three CBP’s, (CBP-1, 2 and 6), one of 300 cum/hr, second of 30

cum/hr and third 30 cum/hr capacity will be deployed. For APP-3 works one CBP-2 of 30 cum/hr



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shall be deployed. For APP-2 works two CBP’s one 30 cum/hr (CBP-4) and second 60 cum/hr

(CBP-5) capacity CBP will be deployed. The location of the CBP’s are given here in below:-

• 300 cum/hr capacity CBP-1.

• 30 cum/hr capacity CBP-2





16.3 DIVERSION ARRANGEMENT

The Hirong HE Project envisages construction of a Concrete Gravity dam having its

anticipated deepest foundation at 1225m with top of dam at 1358.50m. Thus the height of dam

from the deepest foundation level is 133.50m. Diversion arrangement for construction of

concrete gravity Dam of Hirong HE Project comprises of:

i). A Diversion Tunnel 10.15m dia Horse-shoe (modified) shaped, concrete lined and 473m

long.

ii). An Adit D-shaped 7m diameter and 280 m long.

iii) An Upstream concrete coffer dam with top at 1251m, 65.6m long at top.

iv) A Downstream concrete coffer dam with top at 1242m, 50.4m long at top.

In view of the better geology on the right bank of river Siyom, the diversion arrangement

has been planned on the right bank. The left bank is readily accessible and to have access to right

bank, a bridge on river Siyom along with access roads will be needed. However to take up the

construction of adit and DT, the equipment will be taken on the right bank in dismantled

condition by barges and by the time the excavation has been done, the access to this bank would

be established.

16.3.1 Sequence of Construction of Diversion Arrangement

Thus the sequence of construction shall be as below :

i) Excavation of adit after establishing its portal

ii). Establishment of junction of Adit and DT such that the invert of adit at the tunnel grade is

at 1239.659 i.e. the benching level of DT.

iii) Excavation of heading of DT both towards u/s and d/s side and leaving a rock plug at

both the u/s and d/s portal ends.



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iv) Regarding of adit invert in a length of about 36m to meet the invert of DT at the junction

i.e. 1236.609 m elevation

v) Invert excavation both on upstream and downstream side.

vi) The structures at the inlet and outlet of DT to be established along with the activity 1

above during non-monsoon period after making ring bunds

vii) Overt and invert lining of DT after activity 5 above followed by grouting.

viii) Removal of u/s and d/s plugs in DT, which were left earlier.

ix) Erection of H.M. equipment.

x). Construction of plug at the junction of DT and adit (before diverting river water into the

DT)

16.3.2 Underground Excavation of 7.0 m D-shaped Adit

The excavation of 7.0 m D-shaped (finished) Adit to Diversion Tunnel would be taken up

by drill/blast method tackling full face excavation, as soon as the portal is established. The

drilling shall be done by Two-Boom Hydraulic Jumbo and removal of excavated material shall

be done by a combination of 2.5 cum side dump loader and 20 ton capacity rear dumpers. The

excavated area of 7 m, D-shaped Adit to DT is 48.67 sq m at minimum excavation line.

Assuming twenty (20) working hours in a day and twenty five (25) working days in a month, the

monthly progress of 7.0 m D-shaped Adit works out to about 85 m.

16.3.3 Junction between Adit and DT:

After the Adit excavation, construction at the junction of Adit and DT will be completed.

This will involve widening of Adit just before it joins the DT and installation of shotcrete, rock

bolts and rib supports. Adjoining the junction the section of DT shall be kept marginally wider

than the regular size of Diversion Tunnel, to adequately support the Rib-arches in the Haunches.

After the junction area of Diversion Tunnel is excavated and adequately supported, excavation of

DT in the upstream and downstream of the junction will be taken up.

16.3.4 Excavation of 10.15 m dia Modified Horse-Shoe Shaped Diversion Tunnel

The excavation of DT will be done by heading and benching. The heading will be kept

7.5m such that bottom level of heading is at 1239.659 m and benching at 3.45m. The 10.15m

diameter Modified Horse-shoe shaped Diversion Tunnel having a length of about 473m would

largely be excavated in rocks of varying quality. The excavation of DT is to be done by using

Drill and Blast method (DBM). The Diversion Tunnel will have a lining thickness of 400mm,



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accordingly the minimum excavated dia as well as excavated vertical dimension will be 10.95m

with 8.0m base width. The excavation and lining of diversion tunnel will require about 12

months as such at least one monsoon season resulting in high water levels / flows in the river

Siyom has to be faced by the under construction diversion arrangement. The drilling of holes will

be done by Two Boom Hydraulic Jumbos. Haulage of excavated material shall be done by a

combination of 2.5 cum side dump loader and 20 ton capacity rear dumpers.

16.3.5 Ventilation

At the time of excavation of tunnels, adequate provision for proper ventilation is

absolutely essential, therefore an effective ventilation arrangement has been planned during

execution of Adit and DT. It is proposed to provide two fans ZVN-1-14-110/4 in series with a

circular ventilation duct of 1.4 dia. As soon as the tunnel is through, ventilation will not be

required. Following criterion have been adopted for provision of ventilation arrangement.

16.3.6 Concrete Lining of DT

After the excavation in heading followed by benching is completed, the invert of the

Diversion Tunnel will be properly dressed and a 100mm thick layer of lean concrete (PCC M10)

shall be laid to form the level base at the requisite invert slope to be maintained in the Diversion

Tunnel in downstream. Suitable shuttering will be done and lining concrete of 400mm thick shall

then be paced at invert base and on sides, up to 2m height.

While the overt lining for the downstream reach is in progress, simultaneously the invert

laying in the upstream reach would be carried out. After the completion of overt lining on the

downstream side the shutter would be moved from downstream side to the upstream side, where

the invert would have been laid by then for the length of the reach such that it can accommodate

the shutter easily. At the time of execution of Diversion Arrangement, it is planned to set up a

Concrete Batching Plant of 30 m3/hr capacity and to cater for the requirement of Aggregate, an

Aggregate Processing Plant of 60 TPH (APP-3) shall be provided nearby CBP (CBP-2). At the

time of construction of Diversion Arrangement, an weighted average lead of about 1.2 km has

been considered from CBP-2 to the Portal of Adit to Diversion tunnel.

16.3.7 Removal of Rock Plugs

When the contact grouting on the upstream side is being carried out, rock plug on the

downstream side will be removed by excavation in heading and benching and adequately



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supported with the help of rock bolts / ribs as the case may be. Then the invert for this reach

would be laid. While the shutter for the lining in the reach occupied by the downstream rock

plug is being erected, the upstream rock plug would be removed by excavation in heading and

benching.

16.3.8 Inlet and Outlet Structures

During the time when all the above cited activities viz. excavation of Adit and DT,

establishment of Adit portal, raising of small ring dykes and concreting lining of DT are going

on, following activities will also be carried out concurrently in the sequence given below:

i). Removal of overburden material and excavation for Portals at the Inlet and Outlet ends of

DT

ii). Concreting for structure of portals at the Inlet and Outlet

iii). Raising of 4m high earthen ring dyke for the inlet structure and 3.5m high for the outlet

structure.

iv). Reinforcement and Concreting for the walls of the Box RCC structure duly fixing the first

stage embedment of gates

v). Excavation of toe wall

vi). Concreting of toe wall

vii) Reinforcement and concreting of roof of the inlet and outlet structures

viii) Laying of CC Blocks in front and on sides of inlet and outlet structures

ix). Invert of the inlet and outlet structures

x). Second stage concreting for gates in the groves etc.

xi) Lowering of gates and installation of HM equipments.

xii) Removal of earthen dykes.

16.3.9 Methodology for Erection of Main H.M. Equipment

Following shall be the typical erection sequence of Vertical fixed wheel gate

components:-

i) Erection of the first stage embedment (anchor bolts) in the blockout left in the RCC walls.

ii). Each set of guides, and seal seat arrangements shall be assembled in the respective

blockouts, secured in place by anchorages.

iii). Placement of second stage concrete in blockout

iv). Gate/Stoplog units transported in sub-assemblies by trailer and shall be assembled and

erected by suitable mobile crane



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v). Rubber seals shall be fitted with gate to make it leak proof.

vi). Suitable Hoisting arrangement shall be installed at 1262 m. for Inlet and 1253m for

Outlet.

16.3.10 Plugging of Adit

The Diversion Tunnel has to be ready for diverting the river water along with plugging of

Adit before the Earthen dykes for concreting of closure of coffer dams is taken up. At the same

time the last few activities in the diversion tunnel which are removal of rock plugs, concrete

lining of the respective reaches upstream and downstream along with contact / consolidation

grouting have to be completed prior to commencement of work on the construction of earthen

dykes. These earthen dykes would be constructed for closure of coffer dam only after the

diversion tunnel is fully ready for passing of the diverted water of the river i.e. the Diversion

Tunnel is complete in all respects and the Adit has been plugged.

16.3.11 Coffer dams

Diversion of river water shall be carried out for taking up the construction of main dam.

The upstream cofferdam shall be founded at 1234m and downstream cofferdam shall be founded

at 1231m depending upon availability of rock. The u/s and d/s coffer dams are planned to be

constructed using pumped concrete of grade M15A20/A40 and are likely to have maximum

heights of 17-18m and 09-10m, respectively. On completion of all the works related to DT,

plugging of Adit and removal of earthen dykes provided at the Inlet and Outlet structures will be

taken up so that the river water gets diverted to DT and raising of earthen dykes for the coffer

dams can be taken up.

For the closure of the coffer dams, earthen dykes would need to be constructed. From the

water availability series evolved for the Hirong HE Project it is seen that maximum 10-daily

inflows during the Jan, Feb and March months are 94.60, 125.42 and 102.34 cumecs. As such the

closure of the coffer dams has to be planned during the months from January to March.

16.4 DAM AND INTAKE

The construction methodology for the main dam mainly consists of (a) excavation of bed

up to sound rock profile (b) Treatment of shear zones, if any (c) Laying of concrete in lifts of 2.0

m thickness (d) Consolidation grouting (e) Curtain grouting (f) Drainage holes (g) Laying of

spillway bridge (h) Erection of hydro mechanical equipments.



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16.4.1 The Sequence of Construction

The quantities of main items i.e. excavation and concrete to be executed in these

structures are as below:

Dam Blocks:

1. Open excavation in gravels and boulders 1,19,733 m3

2. Rock excavation 1,74,003 m3

Trajectory impact pit



Left Bank excavation between dam blocks and trajectory impact pit

1. Open excavation in gravels and boulders 88,985 m3


Excavation for Road between dam blocks and trajectory pit on left and right bank


2. Rock excavation 36,074 m3

Total quantities of excavation in dam blocks are as below:



Total quantities of excavation in intake structure are as below:


2. Rock excavation 11,964 m3

Total quantities of concrete are as below:

(1) (a) In Dam Blocks 11,16,093 m3

(b) In CC Blocks d/s of dam 1,300 m3

Total 11,17,393 m3

Total quantity of concrete in intake 20,277 m3

The civil works for Main Dam and Intake are planned to be executed in five working seasons.

i) First Working Season (16th Oct 2012 to 15

th May 2013)

ii) Second Working Season (16th Oct 2013 to 15

th May 2014)

iv) Third Working Season (16th Oct 2014 to 15

th May 2015)

iv) Fourth Working Season (16th Oct 2015 to 15

th Oct 2016) :

v) Fifth Working Season (16th Oct 2016 to 15

th Sep 2017)



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16.4.2 Excavation Methodology

For excavation in overburden material, combination of Ex-400 hydraulic excavator (2

cum bucket) and dumpers shall be used. For rock excavation, drilling and blasting shall be done

with crawler drills (with compressors). In addition, rock drills with or without pusher legs will

also be used. The loading and haulage equipment will be same as for excavation in overburden

material. The excavators shall be assisted by Dozers as needed. The type and number of

equipment required has been worked out in paragraphs on equipments.

16.4.3 Methodology for Concrete Placement

The concerting of dam blocks essentially consists of three main activities viz.

manufacture of concrete which includes Aggregate Processing Plant for production of Aggregate,

Batch and Mixing Plant and Ice Plant for production of ice. Aggregate processing plant and

Batch/Mixing Plants shall produce concrete for Dam, Intake as well as for other components of

the project such as HRT lining components of the project. The maximum concrete requirement

for placement of concrete in Dam Blocks is 200 m3/ hour. The Aggregate Processing Plant of 500

t/hr capacity shall be installed for production of aggregate and Batch/ Mixing plant of capacity

300 cum/hr shall be installed for production of concrete (Refer Chapter on Common works). The

ice plant of 90 t/hr capacity shall be installed so that required quantity of ice may replace the

water to be mixed in concrete to bring the production temperature of concrete to 10°C. The

placement temperature of concrete as worked out by thermal studies is 12°C. It has been assumed

that the temperature of concrete will rise by 2°C by the time it reaches from batch mixing plant to

the placement location.

16.4.4 Equipment Required for Works of Dam and Intake

List of equipment required for works of Dam and Intake Structure is as below

i). Ex-400 Hydraulic excavator/equivalent 2 Nos.

ii) 20 t capacity dumpers 9 Nos.

iii) Crawler/ wagon drills IRCM-341 4 Nos.

iv) Compressor 450 cfm 4 Nos.

v) Compressor 1000 cfm 2 Nos.

vi) Dozers 180 HP/equivalent 2 Nos.

vii) JCB Back Hoe 2 Nos.

viii) Radial Cable Cranes (9 m3 capacity) 2 Nos.

ix) Concrete buckets (9 m3 capacity) 4 Nos.



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x) Silo Buses 10 Nos.

xi) Concrete pump 38cum/ hr 2 Nos.

xii) Transit Mixers (6 cum capacity) 3 Nos.

xiii) Needle Vibrators (65 mm dia. Needle) 6 Nos.

xiv) 150 mm dia Needle Vibrators with frequency changers 2 Nos.

xv) Mobile crane (Hydra) 8/10 capacity 2 Nos.

xvi) Air water Jet Blaster 2 Nos.

xvii) Sand Blasting Equipment 2 Nos.

xviii). Grout Pump SURFEX with capacity of 50 lit/min 2 Nos.

at 1.5 N/mm2 pressure

xix) Drilling machines Diamec 262 2 Nos.

xx) Dozers D-50 (wheel Mounted) 2 Nos.

xxi). Dry shotcrete Machine 4/6 m3 per hour 2 Nos.

16.5 HEAD RACE TUNNEL

The total length of the 7.5 m dia (finished) circular shape Head Race Tunnel, aligned on

right bank of river Siyom is 9202 m. Tunnel with a circular shape will be concrete lined having a

finished diameter of 7.5 m. The alignment of tunnel has been fixed in such a way that adequate

lateral and vertical rock cover is available at any particular location.

16.5.1 Infrastructure

In order to access the work sites on right bank from the BRO road on the left the

following basic infrastructure is required to be in place before taking up the tunnel excavation.

Two no. bridges of approximately 60 m and 80 m span shall be needed to access the Adit

locations. One steel girder bridge of 80 m span is proposed to be erected on river Siyom near

Powerhouse location at an Elevation of ± 1040 m. A suitable diversion road from existing BRO

road will be provided to connect the bridge location which will provide access to Adit near Surge

Shaft and Intermediate Adit no.-2. Second bridge of 60 m span across Siyom river is proposed to

be erected upstream of junction of Sitten Nallah with Siyom river. The bridge will provide access

to Inlet adit and Intermediate Adit no.-1.

16.5.2 Construction Methodology and Equipment Planning

The excavation of HRT will be done by using Drill and Blast Method (DBM). The

excavation of HRT shall be done by using four Adits of 7.0 m D-shaped i.e. Inlet Adit,



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Intermediate Adit-1 and 2 and Adit to HRT near Surge Shaft. The above Adits meet the HRT at

chainage 596.12 m, 3029.228 m, 5876.828 m and 9097.974 m respectively. Thus eight faces are

available for excavation of HRT.

16.5.2.1 Excavation

After jungle clearance and construction of roads and bridges, the excavation of Adit

portals will be taken up. The overburden will be removed with the help of Excavator and Dozer

whereas open excavation at portal face will be carried out by conventional Drill Blast Method

with the help of Jack hammers and portable compressor. The mucking will be done by Excavator

and Dumpers. The rock above the portal face will be excavated in a stabilized slope.

Four no. Adits (7.0 m D-shaped) will be provided for excavating HRT having total length

of 9202 m. The location of Adits has been fixed keeping in view the geological and

topographical conditions as well as construction convenience. The size of Adits has been kept as

7.0 m D-shaped keeping in view the easy movement of mucking equipment. The slope of various

adits has also been kept mild in order not to stress the loaded equipment unnecessarily. A

positive slope to all the adits has been provided in order to make them self draining. The

excavation of Adits has been planned to be carried out full face by normal Drill and Blast

Method as soon as the portals are established. The drilling operation for excavation of Adits is

proposed to be carried out by deploying two-boom drilling jumbos and mucking will be done

with the help of side tilting loader (2.5 cum) and 20 T capacity dumpers.

16.5.2.2 Head Race Tunnel (Heading)

The excavation of heading will be carried out in following operations.

i). Survey and marking of profile

ii). Drilling operation Drilling will be done by using two boom hydraulic drilling Jumbos,

which can theoretically drill up to 2 m per minute say 100 m per hour of 50 minutes

working)

iii). Charging and Blasting (The holes drilled will be loaded by Powergel or equivalent. Non-

electric detonators with millisecond delay are proposed to be used.

iv). Defuming (At the time of excavation of tunnels, adequate provision for proper ventilation

is absolutely essential; therefore an effective ventilation arrangement has been planned

during excavation of tunnels).



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v). Scaling (The scaling is proposed to be carried out manually with help of scissors

platform.

vi). Mucking

vii) Rock Support Measures (Shotcreting shall be carried out up to excavated face after each

blast whereas rock bolting shall be provided about 2 pulls behind the excavated face).

16.5.2.3 Head Race Tunnel (Benching)

After heading operations are complete between two Adits, the benching of 1.2 m will be

carried out by conventional bench blasting method. The progress targeted for benching

operations is 20 m per day i.e. a monthly progress of 500 m. Same equipment as provided for

heading excavation shall cater for benching operations as well.

16.6 EQUIPMENT PLANNING FOR TUNNEL EXCAVATION

The planning of equipment has been carried out based on following data.

i). Excavated Tunnel Area at minimum excavation line (heading) 49.94 m2

ii). Excavated Tunnel Area including payline and 5% over excavation (heading)52.44 m2

iii). Blast Hole diameter 41 mm

iv). Empty hole diameter 102 mm

v). Advance per pull 3 m

vi). Drilling Equipment Two boom hydraulic drilling Jumbos

vii). Theoretical rate of penetration 2 m / minute

or 100 m / hour

viii). Actual anticipated rate of drilling 80 m / hour

ix). Swell Factor 1.5

x). Estimated loose muck per pull 235.98 m3

xi). No. of drill holes 110

xii). Depth of drilling for each hole 3.5 m

xiii). Total drilling involved 385 m

16.7 CONCRETE LINING OF HRT

The concrete lining in HRT is proposed to be carried out after completion of benching.

The lining is proposed to be carried out by using three set of shutters (each set containing two

shutters and one traveler). The sequence of concrete lining operations in overt will be as follows:



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i). One set of shutter will be installed at chainage 0.0 m. This shutter will move towards Inlet

Adit (Ch. 596.12). After completion of this reach the above set of shutter will be

dismantled and installed at chainage 3029.228 m. This shutter will move towards the Inlet

Adit. For supply of concrete 30 cum/hr capacity CBP installed at Inlet Adit will be used.

ii). Second set of shutter will be installed at chainage 5876.828 m and lining will proceed

towards Intermediate Adit-1. The 30 cum/hr capacity CBP installed at the portal of

Intermediate Adit-1 will be used for concrete placement.

iii). Third set of shutter will be installed at upstream end of Surge Shaft at chainage 9202 m

and lining will proceed towards Adit to Surge Shaft i.e. 9097.974 m. The concrete during

this reach will be supplied from CBP of 30 cum/hr capacity installed at portal of Adit to

Surge Shaft. After completion of lining from chainage 9202 m to Ch. 9097.974 m the

above set of shutter will be installed at chainage 9097.974 m and the lining between the

two chainages i.e. 5876.828 m and 9097.974 m will be completed and concrete will be

supplied from 30 cum/hr capacity CBP installed at portal of Intermediate Adit-2.

16.7.1 Grouting

16.7.1.1 Contact Grouting

Contact grouting in the tunnel is proposed to be carried out after 30 days of placement of

concrete in tunnel invert. After this the contact grouting will progress simultaneously with lining

activity of tunnel. Contact grouting is provided to fill any gap, especially at crown level, which

has been left during concreting activity between rock and concrete lining. For this purpose grout

holes of 38 mm diameter will be drilled 300 mm inside the rock and grouting will be done at a

low pressure of about 1 to 1.5 kg/cm2. The water cement ratio in the beginning will be kept

leaner and the same will be thickened as grouting progresses.

16.7.1.2 Consolidation Grouting

The same holes as utilized for contact grouting will be re-drilled up to a depth of 6m for

consolidation grouting. The consolidation grouting will be done at a pressure ranging from 5

kg/cm2 to 7 kg/cm

2. The consolidation grouting in this case will also be carried out till refusal.

16.7.1.3 Plugging of Adits

Once the grouting operations in the tunnel as well as all other activities in adjacent

components i.e. Surge Shaft and Intake are completed the Adits will be plugged with concrete.

For this purpose adequate no. of Shear keys will be provided. To fill any gap between rock and



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concrete plug the consolidation grouting will be carried out after plugging operations have been

completed. Two no. adits i.e. Adit near Surge Shaft and Inlet Adit are proposed to be provided

with a vehicular access each.

16.7.1.4 Cleaning of HRT

After completion of all activities the tunnel is to be thoroughly inspected for any foreign

material left inside during construction. This will ensure that no

16.7.2 Construction Equipment for HRT

The summary of equipment is given below

Sl. No Construction Equipment Quantity

A. Drilling and Blasting Equipment

i). Portable Compressors – 1000 cfm 6

ii). Two boom drilling Jumbos 6

iii). Crawler drill IRCM – 341 along with 450 cfm compressors 4

iv). Jack Hammer with Pusher legs 12

B. Mucking Equipment

v). Wheel mounted Dozer (180 HP) 3

vi). Loader 2.5 m3 bucket capacity side Dump Loader 6

vii). Dumper (20 T) 30

C Concrete Production and Placement

viii). Aggregate Processing Plant – 500 t/hr Capacity 1

ix). Aggregate Processing Plant – 100 t/hr Capacity 1

x). Aggregate Processing Plant – 60 t/hr Capacity 1

xi). Concrete Batching Plant - 30 cum/hr Capacity 4

xii). Tunnel Shutters with Vibrators – Complete (each of 12 m length)6 (with 3 travelers)

xiii). Needle Vibrator - 65mm diameter with flexible shaft. 10

xix). Transit Mixers - 6 cum Capacity 9

xv). Concrete Pump (38 cum/hr.) 3

xvi). Surge Hopper 3

D Shotcrete, Drilling and Grouting

xvii). Wet Shotcrete Machine with Telescopic Arm 4

xviii). Grouting Pump (Surfex / Mai) 4

E Support Equipment for Underground Works

xix). Ventilation Fans 1400mm dia Impeller 13

xx). Ducting 1400mm dia 10718

xxi). Scissors Platform 4

xxii) Rib Erector 4

xxiii). Rib Bending Machine with Jack etc. – Complete 1

xxiv). Alignment Lazer 6

xv). Profiler 6



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16.8 SURGE SHAFT

The Head Race Tunnel terminating in a 15.0m finished dia and 140.25 m high Surge

Shaft at RD 9217.53 m. The excavated dia of surge shaft is 17.20m (including 1000 mm thk

lining and 100 mm thk shotcrete) from 1277.75 m to 1388.00 m and 18.10 m (including 1450

mm thk lining and 100 mm thk shotcrete) from. 1388.00 m to 1418.00 m. The location of Surge

Shaft has been so planned that sufficient cover is available on all side of Surge Shaft. Sufficient

space has also been ensured for working of a gantry crane at top to facilitate widening of pilot

shaft and supply of concrete for concreting operations.

16.8.1 Construction Methodology

16.8.1.1 Excavation

An independent road to Surge Shaft has been provided which will be completed after

twenty months from start date of project. A bench is proposed to be excavated at 1418 m. The

surge shaft is connected at its bottom through an adit which is connecting HRT, valve chamber

and adit to top of penstocks. Excavation of Surge Shaft will be carried out in two stages i.e. Pilot

Shaft and widening.

The excavation of pilot for Surge Shaft is proposed to be carried out from Adit to HRT near

the Surge Shaft bottom. For this purpose an Alimak raise climber will be installed at the bottom and a

pilot of 2.6 m diameter will be excavated with the help of raise climber. If needed the temporary rock

support by way of spot rock bolts of 2 to 2.5 m length shall be provided in the pilot shaft.

A temporary winch of 10 T capacity will be installed for carrying out the sinking

operations. A Tripod will be erected over top of pilot shaft from where the sinking operations

will be carried out. Mucking in this case will have to be carried out manually. In case rock is very

much shattered in top reaches the shaft will be supported by providing temporary steel supports.

A 30 T capacity gantry crane will be installed at top of surge shaft for lowering and lifting

excavation equipments, men and material as the excavation for widening proceeds. Widening

operations shall be taken up proceeding from top to bottom by drill and blast method for 1.0 m

depth at a time. The muck generated after blast will be dozed of by a small dozer upto pilot shaft

and will be collected at bottom of surge shaft from where it will be hauled to nearest dumping

site. The above sequence shall be repeated until the entire depth of the Surge Shaft is excavated.

Total depth of Surge Shaft to be excavated in this manner is around 140.25 m. Normal benching

operation shall be followed while widening of surge shaft.



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In the initial reach of about 30 m from the top the widened Surge Shaft is proposed to be

supported by composite steel section of ISMB 300 x 140.25 with plates of 16 mm welded on

both flanges and concrete. The ISMB will be completely embedded in concrete with a cover of

150 mm on its front face.

16.8.2 Equipment Planning

16.8.2.1 Open Excavation at Surge Shaft Top

Open excavation to the extent of 12740 cum is to be carried out for which three month

time has been provided in construction schedule. The excavation will be carried out by using

Jack Hammers and a portable compressor of 500 cfm. A loader will be used to load dumpers of

20 T capacity. Since muck generated is only 13.6 cum/hour which is almost equal to carrying

capacity of one 20 T dumper as such only one loader and dumper are sufficient to meet with the

requirement. In addition one Crawler Dozer 180 HP shall be provided for dozing and collection

of muck at the excavation site.

16.8.2.2 2.60 m dia pilot Shaft from Bottom

Pilot shaft of 2.6 m diameter is to be excavated by deploying one no. Alimak raise

climber at bottom of Surge Shaft. A progress of 1 m per day will be achieved by raise climber.

As such four months time period has been provided in the construction schedule for this purpose.

Since the muck generated per day is only of the order of 8.31 cum after considering a swell factor

of 1.5 for loading and haulage of this muck a loader and a 20T dumper will be provided at

bottom of Surge Shaft.

16.8.2.3 Side Slashing / Widening of Surge Shaft

Widening of surge shaft is to done after completion of pilot shaft with the progress of 10

m / month in top 30 m and 15 m/month in remaining portion for which 11 months time has been

provided. The Drilling will be carried out by wagon drill and a portable compressor of 500 cfm.

A small dozer for dozing and loader will be used to load dumpers of 20 T capacity.

16.8.3 Concreting

The concreting of Surge Shaft is proposed to be carried out by deploying a slip form

shutter. The installation time for slip form shutter will be about two months. Concrete mix shall

be transported from batching and mixing plant installed at adit to HRT near Surge Shaft through

transit mixers feeding 40 cum concrete pumps for concrete lining up to 30 m height from bottom



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of Surge shaft. Concrete lining in rest of the Surge Shaft shall be done from top of Surge Shaft.

Shutter vibrators and needle vibrators shall be used for vibration of concrete. The progress with

slip form shutter will be of the order of 15 m / month and it will take about 9 months to complete

the operation of concrete lining of 138 m deep Surge Shaft. For providing reinforcement a

separate platform will be erected which will move ahead of concrete lining.

16.8.4 Grouting

16.8.4.1 Contact Grouting

The contact grouting is to ensure proper contact of concrete with rock and consequent

load transfer. For this purpose periphery holes will be drilled 300 mm deep into rock and

grouting carried out at low pressure of 1 to 1.5 kg/cm2. The water cement ratio of the grout mix

will be kept leaner in the beginning and thickened consequently. The contact grouting is to be

carried out till refusal of the grout intake.

16.8.4.2 Consolidation Grouting

In order to prevent any loss of water through shear seams and open joints it is necessary,

especially in reach where rock cover is limited, to carry out consolidation grouting. For this

purpose the holes drilled for contact grouting will be redrilled up to 8 m depth and consolidation

grouting carried out through these holes at a pressure ranging from 5 kg/cm2 to 7 kg/cm

2. The

grouting in this case also is to be carried out till refusal. Total requirement of equipment for

concreting in surge shaft are as under: The important equipment required are Transit Mixer 6

cum (Nos. 3), Concrete Pump (1), Needle vibrator (4), Batching and mixing plant 30 m3 cap

(1), Grout pump (1) and Slip form shutter 1.1 height (1).

16.9 PRESSURE SHAFT AND VALVE CHAMBER


For the excavation of Pressure Shafts two Adits, namely Adit to Bottom of Penstock and

Adit to Top of Pressure Shaft have been provided. Bottom Adit off takes from MAT at 1020.00

m. The Adit invert has been kept at 1005.275 m so as to match centre line of penstock with

centre line of unit. The Adit to Top of Pressure Shaft bifurcates from Adit to HRT near bottom of

surge shaft at 1269.756 m further this adit extend to valve house chamber, designated as adit to

top of valve chamber. Thus, the top horizontal reach of Pressure Shafts will be approached by

Adit to top of Pressure Shafts and the bottom horizontal reach by Adit to bottom of Pressure



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Shafts. For approaching vertical portion of Pressure Shafts all the two approaches will be

utilized.

16.9.1.1 Excavation Methodology (Pressure Shafts)

After completion of excavation of Adit to bottom of Pressure Shaft, bottom horizontal

reach from u/s of Adit to bottom vertical bend of Pressure Shafts will be excavated. About 5 to 6

m of vertical portion of Pressure Shaft will be excavated from bottom horizontal reach by

conventional drill and blast method. The Alimak raise climber will then be installed / erected at

the bottom of Pressure Shaft-1 and Pressure Shaft-2 simultaneously. This activity will take about

one month. The Alimak will land on a raised platform about 3 m from invert of bottom horizontal

reach. The mono rail will be fixed in vertical reach manually. After this the Pilot Shaft of vertical

portion will be excavated through Alimak raise climber and monorail extended after each blast.

The size of Pilot Shaft will be 2.6 m i.e. the size of Alimak Platform. The progress of 1 m per day

will be achieved for excavating the Pilot Shaft. Following this sequence the pilot shaft will be

excavated from bottom to top. The methodology adopted remain same in both Pressure Shafts.

For widening of Pressure Shaft an 15 tonne winch shall be provided in Top Adit to

Penstock. Platform will be lowered in the vertical reach of Pressure Shaft from where men and

material will be taken inside the widened portion of Shaft. A progress of 1 m will be achieved for

widening the Pressure Shaft to its full dimensions.

The four branch penstocks from bottom adit towards Powerhouse end shall be excavated

10 m short of upstream Powerhouse wall. The 10 m reach of branch Penstocks shall be excavated

after Powerhouse excavation reaches that level. The excavation in penstock branches (i.e.

bifurcation) will be taken up one after the other. The drilling will be done by 2-boom Hydraulic

Jumbo and haulage of excavated muck will be done by loader, dumper combination. The

excavation shall be done full face with conventional drilling/blasting method.

The excavation of Top horizontal reach both upstream and downstream of Valve House

Chamber shall be carried out after completion of excavation of Valve House. For excavation of

Valve House Chamber, adit to top of Penstock will be further extended to reach top of Valve

House Chamber. The overt of this adit shall match with overt of Valve House Chamber. A

central gullet 6.5 m wide and 6.5 m deep shall be excavated (Activity-I). The central Gullet so

excavated shall be widened to its full width before carrying out the benching down operations



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(Activity-II). The benching down shall be carried out by providing a ramp in a slope of 1:12 to

meet with top of adit to bottom of valve chamber at 1277.00 m (Activity-III). The haulage of

excavated muck shall be carried out from Adit to top of valve chamber. After the completion of

Activity-III the Valve Chamber will be excavated up to 1282.00 m on one side and 1277 on other

side. The ramp removal shall be done from Adit to bottom of valve chamber. The excavation of

rest portion of Valve Chamber will be done by making ramp in a upward slope of 1:12 and the

haulage of excavated muck will be carried out via Adit to bottom of Penstocks. Thus after

completion of this activity i.e. Activity-IV, further benching down up to invert level of Valve

Chamber will be carried out (Activity-V).

The penstock work involves fabrication of steel liners of 4.25.0m and 3.0 m dia, thus

before the fabrication work, exact number and size of each ferrule shall be planned talking into

account the vertical and horizontal bend reaches. For this purpose, a well equipped Ferrule

Fabrication Workshop will be established at site, with the state-of-the-art plant and equipment.

The erection of ferrules shall be started from Adit to bottom of penstock. The erection of bottom

vertical bend shall be carried out first of all. The stepped concrete pedestals (stairs) shall be

provided to facilitate alignment of various pieces of vertical bend. The vertical bend will be

erected in 18 pieces.

After erection of the bottom vertical bend the 5 m vertical pieces of ferrules will be

lowered in the Pressure Shaft with help of 15 tonne winch provided in Adit to top of Penstock.

Backing strip will be welded with upper face of ferrule. The strip will help in proper alignment of

next ferrule. A clear gap of 3 mm will be provided between bevelled edges of two ferrules. The

circumferential welding will then be carried out. The welding flux will be contained with help of

backing strip.

After circumferential welding is completed Ultrasonic Tests will be conducted before

carrying out backfill concrete and erection of another ferrule. After completion of vertical reach

in this fashion the top horizontal bend will be erected in similar manner as bottom horizontal

bend. Erection of ferrules in top horizontal reach upstream of Valve House is an independent

activity and can be carried out after fabrication of ferrules is over whereas, erection downstream

of Valve Chamber shall be carried out after erection of top horizontal bend.



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Erection of ferrules in bottom horizontal reach up to upstream face of bottom adit to

Pressure Shaft will be carried out after bottom bend is erected. The erection of Y-piece and its

testing will be done after this activity is over and ferrules for branch Penstocks will be erected

after their excavation from Powerhouse end is over.

16.9.2 Equipment Planning

Total requirement of equipment for open Excavation, Pilot Shaft and Side Slashing is given

below.

S.No. Equipment Description Pilot Shafts Side Slashing Optimum

requirement

1. Heavy duty 120 cfm jack hammer (auto feed) 2 2 4

2. 2.5 cum capacity bucket loader (80 m3/hr) 1 1* 1

3. Dumper 20 T capacity 1 3 4

4. Air compressor capacity 1000 cfm 1 1* 1

5. Wet Shotcrete machine - 1 1

6. Alimak Raise Climber 2 - 2

7. Winch 15 T capacity - 2 2

16.9.3 Concreting

The backfill concrete behind Steel Liner (ferrules) will be carried out once a ferrule of 5

m length is erected at site. The backfill concrete in vertical reach of Pressure Shaft will be carried

out from top with help of a concrete pump. Similarly in horizontal reaches also the backfill

concreting will be carried out after erection of each ferrule is over.

16.9.3.1 Concreting Equipment Planning

The concrete shall be transported in transit mixers of 6.0 cum capacity. In three shifts

working, total erection time including backfill concrete for a 5.0 m long single ferule is 6 days.

Assuming one shift i.e. 8 hr is dedicated for backfill concrete.

Total backfill concrete behind single ferule = 45.71 cum

Working hours = 8 hr

Hourly concreting program = 45.71 / 8

= 5.71 cum

Handling losses (5 %) = 5.71 x 1.05

= 5.99 Say 6.0 cum

Concrete production rate per hour = 6.0 cum



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Weighted Average Lead = 1.2 KM

Hauling time

(12.5 km/hr (average), transit mixer speed) = 2 x 1.2 x 60 /12.5

= 12 min

Spotting and waiting time at the CBP = 7.6 min

Loading time at the CBP = 6.6 min

Turning, Spotting and Unloading time = 4.95 min

Total cycle time = 31.15 min

Nos of trip of transit mixer per hr of 50 min = 50/31.15 = 1.61

Concrete quantity carried per hour = 1.61 x 6 x 0.66

(assuming 66% efficiency of Transit Mixer) = 6.38 cum

Transit mixer required = 6/6.38

= 0.94 no. Say 1 no.

Total = 1 No.

Hence, only 1 No. pump 38 cum/hr is sufficient for placing the backfill concrete in

penstocks.

16.9.4 Grouting

Contact grouting shall be carried out once the backfill concreting operations are over.

This will be carried out from holes left in steel Penstocks for this purpose. Drilling will be carried

out from these holes up to 300 mm inside the rock and contact grouting at a pressure of 1 to 1.5

kg/cm2 shall be carried out. Total requirement of equipment for backfill concrete in penstock are

as under:

S. No. Equipments Description No.

1 Transit Mixer 6.0 cum 1

2 Concrete pump (38 m3/hr) 1

3 Needle vibrator 2

4 Batching and mixing plant 30 m3/hr cap 1

5 Grout pump 1

16.10 POWER HOUSE COMPLEX

The Power House Complex comprises of two parallel underground caverns having a clear

rock cover of 41m between them. The Power House Cavern is 130m (L) x 22m (W) x 46m (H)



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and houses the Erection bay, Machine Hall and Control Block. The Transformer Hall Cavern is

on the downstream side of the Power House Cavern and is 118m (L) x 15m (W) x 26m (H) and

houses the Generator Transformers and GIS. The 76m (L) x 7m (W) x 10m (H) D.T. Gate

Operating Gallery is located on the downstream side of the Transformer Hall Cavern with a clear

intervening rock cover of 21.50m. The Power House (PH) and the Transformer Hall (TH)

caverns are connected by four nos. Bus Duct Galleries spaced 17m apart from each other. Four

no. Draft Tube tunnels off-take from the bottom of the P.H. Cavern and go up to the bottom of

D.T. gate shaft and further merges into a Collection Gallery forming the TRT for discharging

water into the river. The excavation of the two major caverns i.e. Power House and Transformer

Hall could be done only after establishing of the Approach Adits, viz. 7.5m D-shaped Main

Access Tunnel, a branch Adit (6.5m D-shaped and 158.65m long) off-takes from MAT at RD

255m and meets the bottom of Transformer Hall at 1020m, Another branch Adit (7.5 D-shaped

and 147.25m long), 6.5m D-shaped Adit to top of T.H. Cavern cum Ventilation Tunnel, a branch

Adit (6.5m D-shaped and 95.62m long), 7.5m Dia. Construction Adit cum Surge Gallery, 390m

long with Portal at 1040m


A Steel bridge of approx. span of 80m is proposed on river Siyom u/s of Powerhouse

location at an Elevation of ± 1040 m for which a suitable diversion road from existing BRO road

will connect the bridge location. This bridge will provide access to Portal of Main Access

Tunnel, Ventilation Tunnel, Construction Adit cum Surge Gallery, TRT Outfall and Switch Yard.

The proposed road to MAT portal will further extend to access the Concrete Batching Plant

(CBP-5) of 60 cum/hr capacity located approx. 0.50Km from MAT Portal and Aggregate

Processing Plant (APP-2) of 100TPH capacity located approx. 1.50KM from CBP-5. For timely

completion of the project, it is necessary that the construction of approach roads leading to

various adits from the bridge is started simultaneously with bridge construction for which

necessary equipment.

16.10.1.1 Approach Adits

Following adits have been provided for approaching various components in Power House

Complex.

i). 7.5m D-shaped Main Access Tunnel (MAT),

ii). 6.5m D-shaped Adit to bottom of Transformer Hall offtaking from MAT,

iii). 7.5m D-shaped Adit to bottom of Penstocks offtaking from MAT,



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iv). 6.5m D-shaped Ventilation Tunnel to Top of T.Hall,

v). 6.5m D-shaped Adit to top of P.House offtaking from VT,

vi). 6.5m D-shaped Adit to DT Gate Operating Gallery offtaking from VT,

vii). 7.5m Dia. Construction Adit cum Surge Gallery

16.10.1.2 Excavation of Adits

The excavation of Adits shall be taken up as soon as the portals are established. The

drilling for excavation of adits shall be done by 2 boom hydraulic jumbo and by conventional

drill and blast method using full face excavation methodology and the mucking will be done by a

combination of Side dumping Loader (2.5cum) and 20T capacity Dumpers. As the excavation

proceeds, suitable rock support by way of rock bolts, shotcrete, steel ribs and backfill concrete

shall be provided as per prevalent geological conditions. Drilling for rock bolts shall also be

carried out with two boom drill jumbos. An average progress of 85m for excavation of Adits has

been assumed as per cycle time calculation shown in Appendix-1 of Chapter-3 for Diversion

Arrangement. The size of MAT and VT has been kept as 7.5m D-shaped and 6.5m D-shaped

respectively keeping in view the transportation of largest size of E-M equipment inside Power

House and easy movement of mucking equipment. The slope of various Adits has also been kept

mild so as not to stress the loaded Dumper/Trailer unnecessarily.

16.10.1.3 Power House cavern

First of all, the roof of the powerhouse cavity will be excavated. This will be done through

6.5m D-shaped Adit to top of P.H. Cavern off-taking from the VT and meeting the powerhouse

cavity gable end at its roof level on the Erection bay side. The excavated crown level of the

powerhouse cavity is at 1042.60m which is same for 6.5m D-shaped Adit to top of PH where it

meets the powerhouse cavity. For excavating the roof vault, a central gullet will first be excavated

along the entire length of the powerhouse cavity and in line with the 6.5m D-shaped Adit. The

central gullet will be 7.5m wide with roof having same profile as that of powerhouse cavity.

After completion of excavation for central gullet, 10m wide nitches along the profile of

Powerhouse crown will be provided on both sides of central gullet. These nitches will be

staggered by atleast 25 m along the length on both sides of gullet. This will ensure that full width

of Powerhouse is not excavated in one go and part excavation and supporting is completed in

2/3rd portion along the crown before taking up remaining 1/3rd portion. This will ensure proper

supporting of crown with least initial deformations. The widening of the central gullet to full



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width of the powerhouse roof vault in 22.20m width will be undertaken from the Erection bay

end and proceed towards the Control block end.

After having excavated and supported the roof vault of the powerhouse cavity up to the

1035m, benching down operations up to the Erection bay level at 1019.7m will be taken up.

Initially, the mucking during the benching down of the powerhouse cavern will necessarily

have to be done through the 6.5m D-shaped Adit to top of P.House, as this will be the only

access available. Benching down will be done in stages by making ramps and removing the

same progressively.

In the next phase, i.e. under Stage-V the entire area of the powerhouse will be benched

down to a elevation of .1019.70m which is same as required for the erection bay floor. In

Stage-VII 7.5m wide ramp shall be excavated along upstream wall of the cavity with its

elevation near the control block end being 1012m and that near the Unit Before the end of

Stage-VII, the lower horizontal portions of the Unit Pressure Shafts would have been excavated

up to the U/S wall of the powerhouse cavity. Stage-VIII will thus consist of removal of ramp

and benching down of entire Power House Cavern beyond Erection bay to 1003.20m, which is

the general excavated floor level in powerhouse cavity. Mucking of this portion shall be done

through the lower horizontal portion of Unit pressure shaft-4. Before the end of Stage-VIII, the

Draft tube tunnels will also get excavated through the collection gallery.

16.10.1.4 Transformer Hall Cavern

The Transformer Hall Cavern (THC) is approached at the crown level through the 6.5m

D-shaped Ventilation Tunnel. Another approach is also available through the 6.5m D-shaped

Adit to bottom of Transformer Hall offtaking from MAT, which meets the THC at its invert at

1020m. Also, the Erection bay of P. House and the T. Hall are connected at 1020m by a 7.0m

wide Connecting Gallery.

First of all, the roof of the Transformer Hall cavity will be excavated. This will be done

through 6.5m D-shaped Ventilation Tunnel meeting the T.Hall cavity gable end at its roof level.

The excavated crown level of the T.Hall cavity is at 1046m which is same for 6.5m D-shaped

Adit to top of T. Hall where it meets the Transformer Hall cavity. After completion of excavation

for central gullet, 10m wide nitches along the profile of T. Hall crown will be provided on both

sides of central gullet. These nitches will be staggered by atleast 25 m along the length on both



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sides of gullet. This will ensure that full width of T. Hall is not excavated in one go and part

excavation and supporting is completed in 2/3rd portion along the crown before taking up

remaining 1/3rd portion. This will ensure proper supporting of crown with least initial

deformations. The widening of the central gullet to full width of the T. Hall roof vault in 15.20m

width will be then taken up and the supporting of the roof of the widened portion will also be

done concurrently.

Once the crown of the THC has been excavated, a 6.5m wide ramp with a slope of 1(V)

in 10(H), which is considered suitable for haulage equipment will be excavated first up to

1029.75m in a length of 87.5m. Further, the benching down of the remaining portion of T. Hall

cavern on both sides of the ramp will be done up to 1029.75m leaving the 6.5m wide ramp for

mucking through VT under Stage-III The rock bolting and shotcreting of the final exposed rock

faces of the cavity walls will be done simultaneously. Under Stage-IV a 4.35m wide ramp shall

be excavated from 1029.75m up to invert level of Connecting Gallery to P.House and 6.5m D-

Shaped Adit to bottom of T. hall i.e. 1020 m along the D/S wall of T. Hall cavern. By the time

this activity is over, the excavation of Connecting Gallery to P.House and 6.5m D-Shaped Adit to

T.Hall bottom off-taking from MAT would have been completed and thus the same will be

available for taking up further excavation and mucking operation. In the next phase, i.e. under

Stage-V, the entire area of the T. Hall will be benched down to a horizontal elevation

of1019.50m which is same as required for the Transformer Hall floor. The benching down

operations for each stage shall be similar as adopted for Power House cavern. The mucking under

this activity shall be done through Adit to bottom of T. Hall.

The excavation and support of niche for Oil separator sump along with balance portion of

Drainage and Dewatering Tunnel between PHC and TH and TH and DT Gate Operating Gallery

will be taken up next. The mucking under these activities shall also be done through Adit to

bottom of T. Hall. The drilling for underground excavation shall be done by Two-Boom

Hydraulic Jumbo adopting conventional drill/blast method for the excavation. Removal of

excavated material shall be done by a combination of Excavator/Side Dump Loaders with

Dumpers. As the excavation proceeds, rock supports system by way of rock bolts, shotcrete, steel

ribs and back fill concrete shall be provided, as required. Drilling for rock bolts shall also be

carried out with Two-Boom Drill Jumbos.



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16.10.1.5 Bus Duct Galleries

Four no. Bus Ducts offtaking from the THC at 1020.00m meets the PH cavern at 1015.20

in a length of 41m each. The excavation of Bus Ducts for a length of 9m shall be taken up partly

from the P.House cavern end as explained above.

16.10.1.6 Draft Tube Gate Operating Gallery

The excavation of 76m (L) x 7.0m(W) x 10m(H) D.T. Gate Operating Gallery (GOG)

shall be taken up as soon as the excavation of 6.5m D-Shaped Adit to DT GOG offtaking from

VT is completed. The crown level of the Gate Operating Gallery is at 1042.10m whereas the

crown level and invert level of Adit where it meets the GOG are at 1038.50 m and 1032.00 m

respectively. The drilling for excavation will be done by 2-boom Hydraulic jumbo (Boomer) and

the mucking of the excavated material will be done by a combination of Excavator/ Side

dumping Loader (2.5cum) and Dumpers through VT. Due to limitation in available working

height of 7.5m for Two-Boom Drill Jumbos, full face excavation of GOG will not be possible.

The excavation of GOG shall be done in two stages

16.10.1.7 Draft Tube Gate Shafts

After completion of excavation of GOG under Stage-II, the excavation for four no. D.T.

Gate Shafts, shall be taken up. It is proposed to erect one no. 10T capacity winch for lowering of

excavation equipments, men and materials for the excavation work. The excavation of Gate Shafts

for Draft Tube-1 and 3 will be taken up first and shall be done in 2 stages each i.e. Stage-III and IV.

The excavation of Gate Shafts for Draft Tube-2 and 4 will be done simultaneously later in Stage-

V and VI each. Under Stage-III, Pilot Shafts each of two meter diameter shall be excavated from

top i.e. at 1031.60m by conventional drill and blast method. After the Pilot shafts for Gate shaft 1

and 3 are completed, widening operations shall be taken up under Stage-IV, proceeding from top

to bottom by drill and blast method for 1.0 m depth at a time. Similar operation is carried out for

excavation of Gate shafts for Draft tubes 2 and 4 under Stage-V and VI.

16.10.1.8 Construction Adit cum Surge Gallery

The excavation of 390m long Construction Adit cum Surge Gallery shall be taken up as

soon as the portals are established. The drilling for excavation is proposed to be carried out by

using two boom hydraulic drilling Jumbos which can safely drill up to a height of about 7.5m.

The finished diameter of circular tunnel is 7.5m and will have maximum excavated height of



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8.25 m in normal reaches and 8.50 m in ribbed reaches. Keeping in view the limited reach of

drilling Jumbo, It is proposed to carry out the excavation in 2 stages- heading and Benching.

16.10.1.9 Tail Race Tunnel, Collection Gallery, Draft Tube Tunnels and Outfall Structure.

The length of Tail Race Tunnel is 210m long and has a circular section with finished

diameter of 7.5m. The TRT is proposed to be excavated from Construction Adit cum

Downstream Surge Gallery which is also of similar sectional profile. The Construction Adit

meets the TRT at 10m D/S of junction of TRT with Collection Gallery.

16.10.1.10 Tail Race Tunnel

The concrete lining in 7.5 m finished dia. circular shaped and 210m long Tail race Tunnel

is to be carried out once the concreting works of D.T. Tunnels including D.T. Gate Shaft and

Collection Gallery are completed. Concrete lining operation consists of Kerb laying, overt lining

to be followed by invert lining. The overt lining shall be done using a 12m long hydraulically

operated collapsible Gantry Shutter moving on rails. The rails shall be fixed on kerbs to facilitate

movement of the shutter. The concreting of invert portion will be done after the overt lining is

completed.

One no. 12m long Gantry shutter will be erected at d/s end of TRT near rock ledge. The

lining operations in this case will be carried out in upstream direction towards junction with

surge gallery. The concrete will be fed from 60 cum/hr capacity CBP-5 installed near MAT

portal. The concrete behind the Shutter shall be placed by Concrete Pumps (38cum/hr capacity).

A Surge Hopper shall be kept near the concrete pump to ensure uninterrupted supply of concrete

to the Pump. Vibration of concrete shall be accomplished by surface vibrators mounted on the

Shutter itself and needle vibrators inserted through inspection window in shutters. While the

lining in this reach is in progress the kerb along with rail fixing will be extended in upstream

reach and the shutter will be moved on rails. The overt concrete lining from up to junction with

collection gallery is completed thus with a progress of 96m/month. The invert lining in TRT will

be done after the overt lining in Surge Gallery is completed. The surface profile of the invert will

be finished to shape by screeding with the help of a tailor made template.

16.11 CONSTRUCTION SCHEDULE

Table 16.1 gives the construction schedule of Hirong H.E. Project



CISMHE

Table 16.1 Construction Schedule of Hirong H.E. Project

S. N. Description Completion Date

i). Diversion Arrangement and River 15.01.2014

Diversion (including u/s and d/s coffer dams)

ii). Main Dam (All four sluice gates erected) 15.12.2017

iii). Intake Structure 15.05.2017

iv). Reservoir Impounding Date 15.12.2017

v). HRT 15.07.2017

vi). Surge Shaft (including gates) 30.06.2017

vii) Valve Chamber (including erection of valves) 15.03.2017

viii). Pressure Shafts 15.09.2016

ix). Transformer Hall 31.05.2017

x). Surge Gallery 31.12.2016

xi). TTR & Outfall Structure (including h/m works) 30.04.2017

xii). Cable Tunnel & Switch Yard 15.05.2017

(including erec. & commissioning of e&m works)

xiii) Power House

a) Water Availability 31.12.2017

b) UNIT-1 - Testing & Commissioning 28.02.2018

c) UNIT-2 - Testing & Commissioning 30.04.2018

d) UNIT-3 - Testing & Commissioning 31.05.2018

e) UNIT-4 - Testing & Commissioning 30.06.2018

CONSTRUCTION METHODOLOGY - APSPCB EIA corrected finally/EMP...Environmental Management Plan –...

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