VOLUME-3 TECHNICAL SPECIFICATION AND GEOLOGICAL REPORT PART-1

DAGACHHU HYDRO POWER CORPORATION LIMITED @HPC)

CONTRACT DOCUMENTS,

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FOR

LOT-1: DAGACHHU HYDRO POWER PLANT (CIVIL WORKS)

TECHNICAL SPECIFICATIONS AND GEOLOGICAL REPORT

DAGACHHU HYDRO POWER CORPORATION LIMITED (DHPC)

Lot-1: DAGACHHU HYDRO POWER PLANT (CIVIL WORKS) Table of Contents

I

Volume

Description Section Contract Agreement and Bill of Quantities I Contract Agreement I1 Letter of Acceptance (LOA) 111 Minutes of Contract Negotiation held on June 1,2009 and June 10 -1 1,2009 in Thimphu, Bhutan N Integrity Pact Priced Bill of Quantities (BOQ) 6.4 Conditions of Contract 1 Instruction to Bidders (ITB) 2 Bid Data Sheet (BDS) 3 Eligibility and Qualification Criteria (EQR) 4 Bidding Forms (BDF) 5 Eligible Countries (ELC) 7 General Conditions of Contract (GCC) 8 Particular Conditions of Contract (PCC) 9 Contract Forms (COF)

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Construction Schedule and Drawings 6.3 I Construction Schedule I Tender Drawings 6.7 Contractor's Bid A I Part-1 of Contractor's Bid B I Part-2 of Contractor's Bid

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Dagachhu HPP

Section 6 - Ernployen Requirements

6.1 Interpretation

Section 6 Employer's Requirements

6.1 INTERPRETATION

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Dagachhu HPP

Section 6 Employers Requirements

6.1 1nte$refllim -Ti

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TABLE OF CONTENTS Section 6.1 Interpretation

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DOCUMENTS COMPRISED N THE EMPLOYER'S REQUIREMENTS

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PRECEDENCE OF THE DOCUMENTS COMPRISED IN THE EMPLOYER'S REQUIREMENTS....................................................................................................................... 1 COGNISANCE

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DEFINITION OF TERMS........................................................................................................... 1 ABBREVIATIONS2

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Dapachhu HPP

Section 6 Emplgvcr's Rcquin'menls

6.1 lntrrprerafion I

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DOCUMENTS COMPRISED I N THE EMPLOYER'S REQUIREMENTS

The Employer's Requirements are described in the following documents, which are hereinafter referred to as the "Specifications" and comprises the following parts:

Pan I1 Requirements: Section 6 Eniployer-s Requirements (ERQ) 6.1 Interpration 6.2 Technical Specifications 63 Conshuction Schedule . 6.4 Bill of Quantities (BOQ) 6.5 National Envimmnent Commission NEC Clearance 6.6 Material Test Reports 6.7 Tender Drawings 6.5 Land Survey and Key Reference Points 6.9 Geological Reporr and Drawinp

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PRECEDENCE OF THEDOCUMENTS COMPRISED IN THEEMPLOYER'S REQUIREMENTS

The several documents Formin:: the Employer's Requirements are to be taken as mutually explanatory of one another. I11 the case of ambiguities or discrepancies. the Employer has authority to issue any instlvction it cor~sidersreasonably necessary to determine any such ambiguities or discrepancies, and the order of precedence shall be the order in which h e documents are listed in clause 1 hereof.

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COGNlSANCE

The Contractor acknowledges that he has copies of all of the documents comprised in the Employer's Requirements.4

DEFINITION OF TERMS

Unless the contrary intention appears: '-Plunt': or "Pmver Plmzi" means the works of Lot I Civil Works and the works of Lot 2 E&M Equipment, which together are capable of proper and reliable production and evacuation of elecmc power in the quality and quantity as described Section 6 Requirements. "Completi(~n means the state of the Works when the Employer issues the Taking- Over Cemficate; " "Divertable Fion," means the total net flow rate measmd in m3lsec that is available for diversion into the Power Station at the Intake Point alter taking account of Compensation Flow requirements; "Facili!ies" means those facilities (including the Power Station) developed within the Works that are to be taken over by the Employer at Completion Date; " H ~ r a l o means the data descn3ed as Probability of Exceedance and River Row at the Intake; ~~" "Sea Level" ineans the mean sea level datum derived From GPS survey and detailed topo-mphical survey as described in Section 6.8 Land Survey and Key Reference Points

"BOQ" means the Bill of Quantities ,which is only indicative for Division 01,02 and 04 and has been provided merely to assist the bidden and to support the evaluation of the Bid, but not to serve as a basis for a unit priced Conaan It does not necessarily cover @erefore each and every item to be delivered/constructed.Bidden shall therefore quote for the entire civil works of Division 01.02 and 04 on a single responsibility basis. C o n w to the Works under Division 01.02 and 04, the Works under Division 03 'Vnderground excavation" shall be offered item by item and will be paid on an item rate basis, that means as per actual quantities according to offered unit rates in the Bill of Quantities. For the Bid documents the expression "Connacror" is equivalent to "Bidder" and "Bidder" becomes "Contractor" in the event of the award of the contract All terms defined in Volume I, Part I (Bidding Procedures -Invitation for Bids) and Part III (Conditions of Contract and Contract F m ) and used herein shall have the meanings ascribed to them in those documents.5

ABBREVIATIONS

The following abbreviations have been used in Section 6 Employers Requirements:"CNT" connection tunnel

.,HRT" Headrace tunnel" A W Access to headrace "SUT' Surge tank "PRY Pressure shaft "PRT' Pressure tunnel "BFC" Biforcator Chamber '3Fl" Bifurcator Tunnel 1 " B W Bifurcator Tunnel 2 "PHC" Powerhouse cavern "GTI" Generator cable tunnel 1

" G W Generator cable tunnel2 'TFC" Transformer cavem"ACT' Access tunnel to powerhouse cavem

"EET' Emergency exit tunnel

'R' T TTailrace tunnelJUl, AU2, AU3,. .." Auxiliary adits

,,SC 1,2, 3 , 4,..." Support classes for rock

Lot-1: DAGACHHU HYDRO POWER PLANT (CIVIL WORKS) Table of ContentsVolume Description Section Contract Agreement and Bill of Quantities I Contract Agreement I1 Letter of Acceptance (LOA) 111 Minutes of Contract Negotiation held on June 1,2009 and June 10 -1 1,2009 in Thimphu, Bhutan IV Integrity Pact 6.4 Priced Bill of Quantities (BOQ) Conditions of Contract 1 Instruction to Bidders (ITB) 2 Bid Data Sheet (BDS) 3 Eligibility and Qualification Criteria (EQR) 4 Bidding Forms (SUFI 5 Eligible Countries (ELC) 7 General Conditions of Contract (GCC) 8 Particular Conditions of Contract (PCC) 9 Contract Forms (COF)

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I NEC Clc;~l;~ncc

Construction Schedule and Drawings 6.3 I Construction Schedule 6.7 I Tender Drawings

..... 1Dagachhu HPP Section 6 -Employer's Requirements6.2 Technical Specifications

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TABLE OF CONTENTSSECTION 6.2 . TECHNICAL SPECIFICATIONS

GENERAL ...................................................................................................... CHAPTER 00 DESIGN WORKS .......................................................................................... CHAPTER 01 SITE INSTALLATION ................................................................................... CHAPTER 02

.. WORK SURVEYING..................DEWATERING ..............................................................................................

ER 03

EARTH & ROCK WORK ........................................................................... CHAPTER 04 CHAPTER 05 UNDERGROUND EXCAVATION ............................................................... CHAPTER 06 CONCRETE & REINFORCED CONCRETE ......................................... CHAPTER 07 WATERPROOFING ................................................................................ CHAPTER 08 STEEL LINING ............................................................................................ CHAPTER 09 DRLLING & GROUTING............................................................................ DAY WORK ............................................................................................... CHAPTER 10 CHAPTER 11

PAINTING........................................................................... CHAPTER 12 STRUCTURAL STEEL WORKS ................................................ CHAPTER 13 METAL WORK .................................................................... CHAPTER 14 MASONRY....................................................................CHAPTER 15 PLASTER WORK ................................................................. CHAPTER 16

. PLUMBING & SANITARY INSTALLATIONS........................ . CHAPTER 17CARPENTRY & JOINERY...................................................... CHAPTER 18 TILING & FLOORING ........................................................... CHAPTER 19 ROADS & PAVEMENTS........................................................CHAPTER 20 ROOFING & SHEET METAL CLADDING ..................................CHAPTER 21

Dagachhu HPF'

Section 6 -Employer's Rcquinments

6.2 Technical Specifications Chapter W General

LOT 1 CIVIL WORKS - VOLUME I1 Part I1 Requirements Section 6 Employer's Requirements

6.2 T E C H N I C A L S P E C I F I C A T I O N S

Chapter 00GENERAL

Dagachhu HPP

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Section 6 -Employer's Requirements

6.2 Technical Specifications Chapter W General . u

TABLE O F CONTENTS Lot 1 Civil Works. Volume II Section 6.2 Technical Specifications

Chapter 00

GENERAL

PAGE1

GENERAL 1 1.1 Scope of work ....................................................................................................................... 1 1.2 Key h j e c t ~ a t.....................................................................................................................2 a 1.3 Diversion weir and Intake ...................................................................................................... 3 1.3.1 Weir Base with Integrated Part of Stilling Basin ...................................................... 3 1.3.2 Grout Curtain and Drain Holes ............................................................................... 4 1.3.3 Side Walls. Wing Walls. Intermediate Wall ............................................................. 4 1.3.4 weir ~ o d ................................................................................................................. y 4 1.3.5 Stilling Basin ............................................................................................................. 4 1.3.6 ~ntake structure ......................................................................................................... 4 1.3.7 Weir Bridge ............................................................................................................... 5 1.3.8. Maintenance and Operation Building ........................................................................ 5 1.3.9 Hydromechanical and Electrical Equipment for Weir and Intake .............................5 1.3.10 Fish Ladder ................................................................................................................ 6 1.3.1 1 Temporary Water Diversion . Cofferdam ............................................................... 6 1.3.12 Consmction Material for Weir and Intake: .............................................................. 6 1.4 Connection Channel and Tunnel to the Desilter ..................................................................... 6 7 1.5 Desilter (Settlement Basin) 1.5.1 Hydromechanical and Electrical Equipment for Desilter ..........................................7 1.6 Headrace ................................................................................................................................. 8 1 6 1 Headrace Channec.....................................................................................................g ..' 1.6.2 Headrace Tunnel North ............................................................................................. 8 1.6.3 Side Adit.................................................................................................................... 8 1.6.4 Headrace Tunnel South ............................................................................................. 9 1.6.5 Hydromechanical and Electrical Equipment for Headrace ....................... ............9 1.7 Swg? ~ a .............................................................................................................................. 9 k 1.8 Press, Shaft and Pressure Tunnel ................................................................................... 10 1.9 Powerhou~e Cavern and Transformer Cavern ...................................................................... 10 1.9.1 Powerhouse Cavern .................................................................................................10 1.9.2 Transformer Cavern ................................................................................................ 11 10 POW^,^,^^ Access Tunnel. Emergency Exit and Cable Tunnel ........................................ 11 ................................................................................................................... 11 12 12 Tailr%ce ~~~~~l and Outlet 3 H~dromechanical Electrical Equipment for Powerhouse ............................................12 and

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Dagachhu HFT


6.2Tshaical Spcifieations Chapter 00 General .iii

1.14 climatic and Catchment Characteristics............................................................................... 15 1.14.1 Catchment and Station Network ................... . ...................................................... 15 15 1.14.2. Precipitation ............................................................................................................. 1.14.3 Temperature............................................................................................................. 16 1.15 Discharge .............................................................................................................................. 17 1.15.1 Long Term Average Runoff .................................................................................. 17 . . 1.15.2 Seasonal Vanahon of Discharge ....................................................................... 18 .. 1.15.3 Low Flow Condlhons ............................................................................................. 19 1.16 Design Flood......................................................................................................................... 20 1.16.1 Dagachhu Flood Frequency Analyses ..................................................................... 20 1.17 Existing Access Roads .......................................................................................................... 21 1.17.1 Recommended Route .............................................................................................. 22 1.18.1 Rellablllty of Power Supply .................................................................................... 22

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1.21 Units of Measurements ......................................................................................................... 23

Dagachhu HPP

Section 6 -Emplayer's Requirements

6.2 Technical Specifications Chapter 00 General - 1

1 1.1

GENERAL Scope of Work

The scope of work is established in the Bidding Conditions, the following Chapters, and in Sub-section 6.7 Tender Drawings of Section 6, ERQ. In addition to the construction of all the related civil works, the Contractor shall prepare the detailed design, all necessary execution drawings, as well as calculations. "asbuilt drawings" and maintenance instructions, etc. Details for the exploration concert of the cavern are given in Chapter 01 Design Works, of these Technical Specifications. The main components of the hydropower plant are: Diversion Weir and Intake Connection Channel and Tunnel to the Desilter Desilter Headrace Channel Headrace Tunnels with Side Adit Surge Tank Pressure Shaft and Pressure Tunnel Powerhouse Cavern and T~ansfonner Cavern Powerhouse Access Tunnel Emergency Exit and Cable Tunnel Conuol Building Tailwater Tunnel including Outlet In addition to the following descriptions, the Tender Drawings shall be referred to.

Dagachhu HPP


6.2 Technical Specifications Chapter 00 G e n d - 2

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Key Project Data676 kmt Dagachhu 41.1 Vs/km2 27.8 m31s 5 m'lsec 733 mill m3

Catchment Area Water Resource Specific Runoff Annual Mean Flow F m Flow (95% availability) Mean Annual Yield (usable) Type of Development WeirIlntake Elevation Desilter Elevation Tailwater Elevation Gross Head Net Head at full load Design Flow (maximum) Design Flow (rated) Installed Capacity Mean Annual Energy Production Energy Production (90% dependable) Turbines Diversion Weir Crest Length Dead Storage Design Flood Rap Gates Radial Gates Desilter (surface) Connection Intake-Desilter Headrace Channel Headrace Tunnels (incl. Side Adit) Surge Tank Pressure Shafi + Tunnel Powerhouse and Transformer Caverns Access and Emergency Tunnel Tailrace Tunnel Transmission Line 220 kV Access roads from Indian Border

excl. Residual Row (1.4 msls) excl. Residual Row and Rood Run of the River max. Water Level Operating Water Level Centre L i e Turbine Runner

843.3 m 841.0m 537.0 m 304.0 m 282.0 m 50.0 m31s 45.0 mYs 114 MW 500 GWh 360 GWh 2 nos.

Pelton Reinforced Concrete Gravity Wall Two sections 2 x 9.1 m HQlO 000 9 . 1 4.0 m ~ 9 . 1 4.0 m ~ 240 x 30.5 x 11 m, incl. transitions Channel L=270 m. Tunnel M 7 6 m

18.2 m 200 000 m3 859 m31s 2 nos. 2 nos. 3 chambers k746m L=261 m L=7795 m Di=21/H=45 m Dk3.4 k540m L679 m 19 km 114km 320 km 62 km approx. 20 km

Di 4.4-4.8 m Vertical Cylinder Reinforced Concrete 250 m and 290 m Horseshoe 4.2515.0 m Powerhouse to Tsirang Substation Gelephu-Sankosh Phuntsholing-Sankosh Sankosh-Chineythang pagana)

access roads to the Sites

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Dagachhv HPP


6.2 Tshnical Specifications Chapter 00 General - 3

13

Diversion Weir and Intake

The weir and intake divert the required amount of water, maximum 50 m3/s, for the operation of the power plant, from the river flow. The structure is designed and equipped to enable the safe passage of the design flood Q1O.OOO, which amounts to 859 m3Is. The weir is situated approximately 900 m upstream from the existing Giuthang suspension bridge in the areas Giuthang, Thalgaon (Lhaling). Close upstream are the Tanalum Chhu and Gomla Chhu, tributaries of the Dagachhu. The operating water level (maximum water level) at the weir is at 843.3 m. The weir is located at a stable, rocky and comparatively narrow portion of the river. The structure is of the reinforced concrete gravity type and shall be founded on solid rock. The 20.7 m wide weir consists of two equal weir units, each 9.1 m wide, separated by an intermediate wall in the middle and side- and wing walls. Each weir unit is equipped with a radial gate at the bottom and a flap gate at the top. The height of the weir from the top of the weir base to the maximum water level is 18.3 m. The overall length of the weir including the stilling basin amounts to approximately 95 m; however the length and the shape of the stilling basin might be modified as a result of the hydraulic model test. The main elements of the diversion weir and intake structure are:-

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Weir base with integrated part of stilling basin Grout curtain and discharge holes Side walls, intermediate wall, wing walls Weir body Stilling basin Intake structure Weir bridge Maintenance and operation building Hydromechanical and electrical equipment Fish ladder Weir Base with Integrated Part of Stilling Basin

13.1

The weir base has to rest on solid rock which is excavated to at least 0.5 m depth, dressed, leveled, cleared of all loose material and the cracks and fissures are filled with concrete and are consolidation grouted. The thickness of the weir base could be reduced to some extent if solid rock is encountered throughout at a higher level. The top of the weir base is steel lined !?om the upstream end of the weir hase to the downstream end of the weir body. At the upstream side, below the weir base, a grout curtain and discharge boreholes are provided to avoid seepage and buildup of water pressure underneath and beside the weir. The weir hase contains an inspection gallery which can also be used for additional drilling and grouting if required, after the completion of the project. The boreboles for the grout curtain and the discharge drilling end there. The grout curtain and the inspection gallery continue along the wing walls. The inspection gallery is permanently accessible through the staircase shaft at the left side of the weir, which also provides access to the weir body. At the top of the shaft, on the ceiling, steel beams are mounted to place a hoist (3 tons) for lifting items to the inspection gallery or the access channel in the weir body. The shaft, ceiling, platforms and staircases are reinforced concrete structures. The shaft has two double wing doors and two windows. Supply and installation of the steel lining of the weir and the supply and installation of the 3 ton hoist are within the scope of Civil Works.

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.-Dagachhu HPP Seclion 6 -Employer's Requirements

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13.2

Grout Curtain and Drain Holes

A row of holes drilled downwards beneath the dam at a defined inclination and depth are filled under pressure with grout until the fissures in the rock are all filled and sufficient water tightness is achieved. This will be controlled by a row of drain holes drilled downstream to the grout curtain.

1.33

Side Walls, Wing Walls, Intermediate Wall

The side walls and the intermediate wall rest on the weir hase. The top level of the walls has a freeboard of 1.2 m above the operating water level in order to avoid overflow during heavy floods. The lower part of the walls in the area of the radial gates is steel lined. The intermediate wall separates the weir in two equal units. Together with the side walls it provides the support for the weir body, radial gates, flap gates, stop logs and the bridge. A pendulum, to be provided by the Civil Contractor, is accommodated in the wall. The upstream end of the intermediate wall is semi circular shaped and steel lined. The lower part of the wall is in the area of the radial gates steel lined on both sides. Supply and installation of the steel lining is within the scope of Civil Works. The wing walls intersect the river embankments and guide the water to the weir. A grout curtain and discharge boreholes are provided in order to avoid bypass flow. The angle of the wing walls towards the river flow could be influenced by the outcome of the hydraulic model test.

1.3.4

Weir Body

The weir body across the river spans between the intermediate wall and the side walls. It forms. together with the weir hase, a monolithic reinforced concrete structure with openings for the radial flushing gates. The weir body, together with the radial gates at the bottom and the flap gates at the lop, provide the harrier across the river for the diversion of the water. The beam-like, f- shaped weir body contains a channel. which is open towards the downstream side and accessible from the left side wall thmugh the staircase shaft. The channel canies part of the electric and hydraulic equipment for the gates and also serves as access for maintenance of the gates. Manholes are therefore provided in the channel floor. On the upstream side the curved pans at the bottom and the top of the weir body are steel lined, supply and installation of the steel lining is within the scope of Civil Works.

1.3.5

Stilling Basin

The stilling basin below the spillway of the dam reduces the speed of the weir overflow, especially during floods, and prevents scouring of the river bed. Part of the stilling basin is integrated in the weir base; the end part downstream is cut into the river bed and the base protected with boulders of suitable size. placed in a concrete bed. Side walls along the stilling basin protect against erosion of the river embankments.

13.6

Intake Structure

The intake structure is integrated into the left wing wall of the weir. The two rectangular intake openings in the wing wall are covered by coarse trash racks. The adjoining intake structure has the shape of a funnel of a rectangular cross-section, which reduces its width to the dimensions of the connection channel. A gate is situated at the end of the intake structure to enable closing of the channel to the desilter in case of high floods, for flow regulation and in case of maintenance requirements. The top slab of the intake structure is designed to bear the weight of loaded trucks and the mobile trash rack cleaner running on rails. No settlements in the ground underneath the tailrace stmcture and the connection channel are allowed; masonry support or cement compacted backfill are required.

55Dagachhu HPP Sectlon 6 - Employer's Requirements6.2 Technical Specifications Chapter W General - 5

1.3.7

Weir Bridge

A reinforced concrete bridge spans over the weir, providing access to both sides of the river. It rests on the side walls and the intermediate wall. The bridge is also required for the installation and maintenance of the hydraulic steel structures of the weir. It therefore has to be designed for heavy transport up to 60 tons. The bridge has detachable railings at both sides. The sliding support of the bridge shall be an elastomer bearing or equivalent.

13.8

Maintenance and Operation Building

At the left side of the weir. near the intake structure, a building for maintenance and operation of the weir will be erected. It is a bungalow of rectangular shape. The foundation base is a reinforced concrete slab; the walls are made of concrete hollow blocks covered by a ceiling of reinforced concrete. The walls are plastered and painted inside and outside. The roof is a timber structure covered with cormgated galvanized iron sheets. The windows and doors are made of aluminum or corrosion protected steel with locking arrangement. The house shall be in the traditional Bhutanese style (e.g. cornice). The house contains a workshop, a transformer station, a standby generator and a control room. All required cable- and pipe ducts from the operation building to the installed electromechanical equipments and for illumination as well as the foundations for the control cubicles, shall be erected by the Civil Works Contractor.

13.9

Hydromechanical and Electrical Equipment for Weir and Intake

The weir will be equipped with two spillway gates (radial gates) and two flap gates. In case of flood, the two flap gates are lowered and the two radial gates are lifted. The two radial gates are placed at the bottom of the weir to provide for proper flushing out of the accumulating sediments upstream the dam and to aid the safe passage of the high floods. The two flap gates mounted at the top of the weir body enable the regulation of the water level, the flushing of floating matter and the safe passage of high floods. The gates are moved with hydraulic cylinders supplied with oil from a hydraulic power unit. The gates can be operated locally or remotely from the powerhouse. For maintenance purposes, stoplogs are set in the upstream and downstream part of the weir. The stoplogs will be lifted and placed with a mobile crane and stored in the dam area, covered with a detachable shed. The supply and erection of the stoplog shed is within the scope of the Civil Works Contractor. The intake area of the channel will be equipped with two coarse racks and one inlet gate. The coarse racks will be cleaned by means of a mobile cleaning machine, running on rails. The intake gate is located downstream of the coarse rack and will cut off the approaching water during maintenance and service of the channel, desilter basin and the intake structure of the headrace tunnel. The gate can be operated either locally at the intake or by remote control. The embedded steel parts in the concrete for the gates and stoplogs shall be provided by the supplier of the hydromechanical and electrical equipment but shall be placed, according to the instructions of the supplier, by the contractor for civil works at the site. The casting of secondary concrete, after fixing of the gates by the E+M contractor, is in the scope of the civil work contractor. Also the supply and placing of all required anchor profiles, niches, pits, slots, cable channels and pipes cast in the concrete structure or put in the ground is in the scope of the civil work contractor. The casting and grouting of the rails and other embedded parts shall be carried out by the civil contractor. Reinforced edges of cable ducts have to be foreseen for cable ways and cable or pipe channels The primary earthing has to be done by the Civil Works Contractor. Stairs and edges with a step of more than 0.6 m have to be provided with a railing with a height of I .0 m

Dagachhu HPP

Section 6 Employer's Requirements

6.2 Technical Specifications Chapter W Fencral - 6

13.10

Fish Ladder

According to the Environmental Impact Assessment report one fish species is known to migrate towards higher altitude during the months of March and April for spawning in the upsueam of Dagachhu. To enable the migration of the fish after construction of the weir, a fish ladder is required. The fish ladder is of the Vertical-Slot-Pass type and has to be designed for an energy density of not more than 140Wlm3. It requires a length of approximately 280m and approximately 15 resting basins. It is a watertight self-bearing reinforced concrete structure, crossing the Tanalumchhu, partly supported by reinforced concrete yokes. The fish ladder is covered with a walkable steel grid, spacing of not more than 5Ox50rnm.

13.11

Temporary Water Diversion Cofferdam

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Prior to the construction of the permanent weir structure, the water will need to be divened to obtain dry ground for excavation and construction of the foundations. This can be achieved by means of cofferdams combined with a diversion tunnel or channel. Bhutan bas a distinct rainy season and a dry period, however the timing may vary and floods are unpredictable. According to the available observations, it can be expected that the Dagachhu discharges are less than 25 m3/s for the period of about five to six months. However, the calculated flood with one year recurrence amounts to 230rn3/s, and the 10 year flood amounts to 400m3/s. This shows that the flooding of the site during the rainy season has to be taken into consideration (refer to Sub-chapter 1.9 Discharge). It is left at the discretion of the contractor to choose the suitable way of river diversion for his work.

13.12

Construction Material for Weir and Intake:

The construction material for the Weir and the Intake is reinforced concrete, which has to be placed in suitable blocks not higher than 4m. The construction and working joints have to be watertight. The temperature development in the concrete has to be kept within the limits given by the relevant standard in order to avoid cracks in the concrete. The concrete surfaces subjected to severe abrasion are coated with mild steel lining not less than 15mm thick. The steel lining has to be anchored into the concrete and the steel plates have to have bond, without gaps to the concrete, this will require, in some instances, contact grouting. The supply and installation of the steel liming is within the scope of Civil Works. Some concrete surfaces subjected to abrasion, such as the base of the stilling basin, are provided with abrasion resistant concrete lining not less than 30cm thick or coated with durable, dressed stone slabs placed in concrete and partly fixed with steel dowels. Concrete quality: C 20125 (fck.cylindcr Nlmm 2,fctCuk= 25 NI mm2), W/C ratio = 0.6 = 20 Steel Reinforcement: Yield Strength, characteristic f, = 500 ~ / m m ' Abrasion resistant concrete: C 35/45, WIC ratio = 0.45, quality and grading of aggregates and sand according to relevant standards. The same concrete quality shall be used for the structural concrete work of all the project components

1.4

Connection Channel and Tunnel to the Desilter

The maximum design flow of 50 m'ls is carried towards the settlement basins by means of an open and a closed reinforced concrete channel and a tunnel, altogether approximately 746 m long. The channel is a reinforced concrete structure of rectangular shape. The portion covered with a slab shall be drivable for loaded trucks up to 18 tons gross weight. The ground along the channel varies from rock to boulders mixed with sand and gravel. Deep reaching compaction (>0.6m) of the loose soil and soil exchange may partly be required. The Gomla Chhu is bridged by a span of 20 m. The foundation and abutments for the bridge are reinforced The river bed below the bridge shall be covered by rip rap in a concrete bedding.

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The connection channel has a horseshoe shape and a concrete lined base and partly full concrete lining or shotcrete lining, depending on the geological conditions. A flushing outlet is foreseen, before the desilter, to enable the cleaning of the connection channel and tunnel. An overflow structure at the beginning of the desilter limits the rise of the water level in case of flow fluctuations and the spillover drops down a cliff into the Dagachbu.

1.5

Desilter (Settlement Basin)

The desilter serves the purpose of removing fine solid panicles from the intake discharge by gravity, down to a grain size of about 0.2 mm. This reduces the abrasion of the water conductor system and the wear of the turbine runners. In addition, floating matter such as leaves, twigs, etc.. will be removed by means of fine screens, which are mounted towards the end of the settlement basins. The desilting basin is located at a comparatively flat area above the left bank of the Dagachhu, near the Giuthang suspension bridge, at an elevation of 841 m (operating water level). The underground consists of rock and sediments. The topographic conditions allow the construction of a triple chamber surface desilter. The desilter is a watertight reinforced concrete structure with the overall dimensions of approximately 240 m length (including transition sections), 30.5 m width and an average depth of 11.0 m. On top of the walls, across the chambers, reinforced concrete beams are supporting the walls. After the inlet gates and before the fine screen the chambers are covered with a slab. The operation and control buildings are placed on the slabs. The settled particles are flushed out from the desilter and diverted through a reinforced concrete channel with the inner dimensions 4 i2.3 m and a length of about 130 m back into the Dagachhu. The bottom and part of the side walls of the desilting chambers and the flushing channel have a steel lining to prevent erosion of the concrete. The supply and installation of the steel lining is within the scope of civil work. Each of the three settlement basins is equipped with an inlet gate, an outlet gate and a flushing gate, tine screens and automatic screen cleaning machines. In order to optimize the desilter design, particularly at the inlet side and to reach a better understanding of the hydraulic behavior of the desilter, a physical model test shall be performed within the scope of the civil contract. In the right wall of the transition paR at the desilter end, an overflow provision is made which spills into the flushing channel. This helps to control the water level in the headrace channel. At the end of the desilter a ramp is provided on the left side so that light vehicles or equipment can have access to the headrace for inspection and maintenance. The access ramp is covered with corrosion protected steel plate elements with lifting hooks. The supply and installation of the steel plates is within the scope of Civil Works. The operation and maintenance buildings have walls made of concrete hollow blocks covered by a ceiling of reinforced concrete. The walls are plastered and painted inside and outside. The roof is a timber structure covered with hard cover (e.g. cormgated galvanized iron sheets). The windows and the doors are made of aluminum or corrosion protected steel with locking arrangement.

1.5.1

Hydromechanical and Electrical Equipment for Desilter

The electm-mechanical equipment necessary to control and operate the desilter is kept in two buildings, which are placed on top of the desilter. Each of the three cambers of the desilter basin is equipped with an inlet and an outlet gate. Dimension of one inlet gate will be approx. 4.5 x 5.6 m: the outlet gates will be 3.5 x 3.3 m. One flushing gate with a dimension of 4.0 x 2.0 m is situated upstream of the inlet gates, three flushing gates with a dimension of 2.7 x 2.0 m for flushing the desilter are situated in the downstream area. The desilter flushing gates can be operated automatically by membranes placed in the desilter bottom. The three inlet and three outlet gates can be operated against full water pressure. The gates can be operated both locally as well as by remote control. The hydraulic load on the gates is transferred through the gate guides into the lining of the gates, . , which transfers the load to the concrete. The hoist mechanism will be installed directly on the slab over the ,-,..*,, ,:\antrance flume.

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6.2 Technical Specifications Chapter 06 Underground Excavation - 5R of 71

8.2.10.4

Powerhouse Cavern -First Bench -Excavation Class B (PHC B l ECB)

Excavation of Bench 1 in powerhouse cavern in competent or jointed rock mass by drill and blast by means of smooth blasting technique, with lengths of rounds between 1.0 and 2.0 metres and subsequent installation of tunnel support before the excavation of the next round. Support elements will be paid separately. 8.2.10.5 Powerhouse Cavern -Second Bench - Excavation Class A (PHC B2 ECA)

Excavation of Bench 2 and all further beneath in powerhouse cavern in competent or jointed rock mass by drill and blast by means of smooth blasting technique, with excavation depths (vertical) not exceeding 3.0 m and installation of tunnel support immediately after exposure of the cavern contour. Support elements will be paid separately. 8.2.10.6 Powerhouse Cavern -Second Bench Excavation Class B (PHC B2 ECB)

-

Excavation of Bench 2 and all further beneath in powerhouse cavern in competent or jointed rock mass by drill and blast by means of smooth blasting technique, with excavation depths (vertical) not exceeding 5.0 m and installation of tunnel support immediately after exposure of the cavern contour. Support elements will be paid separately. 8.2.11 8.2.11.1 Excavation and support of the Generator Tunnel 1 (GT1) Generator Tunnel 1 Support Class 1(GT1 S C 1)

Excavation carried out in competent rock mass by drill and blast by means of smooth blasting of the full face with lengths of rounds between 2.2 and 3.0 metres. For each round, tunnel support shall be installed prior to excavation of the subsequent round, consisting of:-

10 cm of shotcrete lining: 1 layer of wire mesh (100 x 100 mm, 4 kglm2) to be fixed to the rock surface; Swellex (or similar) or SN bolting with 3 m lengths, 3 no. every first round with 4 no. in every second round, at locations required by the discontinuity pattern. Generator Tunnel 1Support Class 2 (GT1 S C 2)

8.2.11.2

Excavation carried out in jointed rock mass by drill and blast by means of smooth blasting of the full face with lengths of rounds between 1.7 and 2.2 metres. For each round, tunnel support shall be installed prior to excavation of the subsequent round, consisting of: 15 cm of shotcrete lining; 1 layer of wire mesh (100 x 100 mm, 4 kglm2), absence of steel rib for fixing of the wire mesh every second round to be considered; Lattice girder steel ribs (70120130) every second round for profile control; A systematic SN rock bolt pattem with 3 m lengths, 6 no. every round with orientations required by the discontinuity pattem. 8.2.12 8.2.12.1 Excavation a n d support of the Generator Tunnel 2 (GT2) Generator Tunnel 2 Support Class 1(GTZ S C 1 )

Excavation canied out in competent rock mass by drill and blast by means of smooth blasting of the full face with lengths of rounds between 2.2 and 3.0 metres. tunr~el support shall be installed prior to excavation of the subsequent round, consisting of: of shotcrete lining; r of wire mesh (100 x I00 mm. 4 kglm2) to be fixed to the rock surface:

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Dagachhu HPP

Seclion 6 - Employer's Requirements

6.2 Technical Specificarians

Chapter 06 Underground Excavation - 59 of 71

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Swellex (or similar) or SN bolting with 3 m lengths, 3 no. every first round with 4 no. in every second round, at locations required by the discontinuity pattern.

8.2.12.2 Generator Tunnel 2 Support Class 2 (GT2 SC 2)Excavation canied out in jointed rock mass by drill and blast by means of smooth blasting of the full face with lengths of rounds between 1.7 and 2.2 metres. For each round. tunnel support shall be installed prior to excavation of the subsequent round, consisting of:-

15 cm of shotcrete lining; 1 layer of wire mesh (100 x 100 mm, 4 kglm2), absence of steel rib for fixing of the wire mesh every second round to be considered; Lattice girder steel ribs (70/20/30) every second round for profile control; A systematic SN rock bolt pattern with 3 m lengths, 6 no. every round with orientations required by the discontinuity pattern.

8.2.13 Excavation of the Transformer Cavern (TFC) 8.2.13.1 Transformer Cavern - Top Heading -Excavation Class A (TFC TH ECA)Excavation of top heading in transformer cavern in competent or jointed rock mass by drill and blast by means of smooth blasting technique, with lengths of rounds between 2.0 and 3.0 metres and subsequent installation of tunnel support before the excavation of the next round. Support elements will be paid separately.

8.2.13.2 Transformer Cavern - Top Heading -Excavation Class B (TFC TH ECB)Excavation of top heading in transformer cavern in competent or jointed rock mass by drill and blast by means of smooth blasting technique, with lengths of rounds between 1.0 and 2.0 metres and subsequent installation of tunnel support before the excavation of the next round. Support elements will be paid separately.

8.2.133 Transformer Cavern - Bench -Excavation Class A (TFC B1 ECA)Excavation of bench in transformer cavern in competent orjointed rock mass by drill and blast by means of smooth blasting technique, with lengths of rounds between 2.0 and 3.0 metres and subsequent installation of tunnel support before the excavation of the next round. Support elements will be paid separately.

82.14 Excavation and support of the Access Tunnel to the Powerhouse Cavern (ACT) 8.2.14.1 Access Tunnel to the Powerhouse Cavern Support Class 1 (ACT SC 1)Excavation carried out in competent rock mass by drill and blast by means of smooth blasting of the full face with lengths of rounds between 2.2 and 3.0 metres. For each round, tunnel support shall be installed prior to excavation of the subsequent round. consisting of: 10 cm of shotcrete lining: 1 layer of wire mesh (100 x 100 mm, 4 kglm2) to be fixed to the rock surface; Swellex (or similar) or SN bolting with 3 m lengths, 5 no. every round at locations required by the discontinuity pattern.

8.2.143 Access Tunnel to the Powerhouse Cavern Support Class 2 (ACT SC 2)Excavation carried out in jointed rock mass by drill and blast by means of smooth blasting of the full face 1.7 and 2.2 metres. support shall be installed prior to excavation of the subsequent

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Dagachhu HPP

Section 6 - Employer's Requirements

6.2 Technical Specifications Chapter 06 Underground Excavation - 60 of 71

-

15 cm of shotcrete lining; 1 layer of wire mesh (100 x 100 mm. 4 kglmz), absence of steel rib for fixing of the wire mesh every second round to be considered; Lattice girder steel ribs (70120130) every second round for profile control; A systematic SN rock bolt pattern with 3 m lengths, 9 no. every round with orientations required by the discontinuity pattern. Access Tunnel to the Powerhouse Cavern Support Class 3 (ACT S C 3)

8.2.14.3

Excavation carried out in weak fractured rock mass by drill and blast by means of smooth blasting of the full face with lengths of rounds between 1.3 and 1.7 metres. For each round, tunnel support shall be installed prior to excavation of the subsequent round, consisting of:-

20 cm of s h o v r e ~ e lining; 1 layer of wire mesh (100 x 100 mm, 4 kg/m2) with steel rib for fixing of the wire mesh; Lattice girder steel ribs (70120130) every round; 25 forepoling bars, 4m length; A shotcrele sealing of the tunnel face with 3 cm of shotcrete; A systematic SN rock bolt pattern with 3 m lengths, 9 no. per round, with orientations required by the discontinuity pattern. Access Tunnel to the Powerhouse Cavern Support Class 4 (ACT S C 4)

8.2.14.4

Excavation carried out in fault zone material andlor weathered rock mass by drill and blast by means of loosening shots andlor tunnel excavator in subdivided excavation steps with lengths of rounds between 1.0 and 1.3 metres. The tunnel face shall be opened in subdivisions and immediately sealed with 5 cm of shotcrete prior to the opening of the next subdivision. For each round, tunnel support shall be installed prior to excavation of the subsequent round, consisting o f 25 cm of shotcrete lining;2 layers of wire mesh (100 x 100 rnm, 4 kglmz) with steel rib for fixing of the wire mesh;

Lattice girder steel ribs (95122132) every round; 31 forepoling bars 3m length (for the next round): A systematic SN rock bolt pattern with 4 m lengths, 14 no. per round, with orientations required by the discontinuity pattern; An invert arch supported with 20 cm of shotcrete and 1 layer of wire mesh (100 x 100 mm, 4 kglm2) with steel rib for fixing of the wire mesh. The sensitivity of the rock mass to water requires particular care: Water shall be kept away from exposed rock surfaces by suitable means approved by the Employer. Ponding water shall not be allowed. 8.2.14.5 Access Tunnel to the Powerhouse Cavern Support Class L (ACT S C L)

Excavation in loose ground by means a tunnel excavator in subdivided excavation steps with lengths of rounds between 1.0 and 1.3 metres. The tunnel face of the pilot holelbench shall be opened in subdivisions and immediately sealed with 5 cm of shotcrete prior to the opening of the next subdivision. For each round, tunnel support shall be installed prior to excavation of the subsequent round. consisting of:-

25 cm of shotcrete lining; 2 Layers of wire mesh (I00 x 100 mm, 4 kglm2) with steel rib for fixing of the wire mesh; Lattice girder steel ribs (95122132) every round; Either 56 driven forepoling bars of 3m length (for the next round). 56 forepoling pipes without of 3m length or 56 forepoling bars without mortar of 4m length; bolt pattern of self drilling bolts with 4 m lengths, 8 no. in the

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Dagachhu HPP

Section 6 - Employer's Requirements

6.2 Technical Specificationr Chapter 06 Underground Excavation - 61 of 71

An invert arch supported with 20 cm of shotcrete and 1 layer of wire mesh (100 x I00 mm, 4 kglm') with steel rib for fixing of the wire mesh, installed at distances not exceeding 6m from the tunnel face. The sensitivity of the ground to water requires particular care. 8.2.15 8.2.15.1 Excavation a n d support of the Emergency Exit Tunnel (EET) Emergency Exit Tunnel Support Class 1 (EET S C 1)

Excavation canied out in competent rock mass by drill and blast by means of smooth blasting of the full face with lengths of rounds between 2.2 and 3.0 metres. For each round, tunnel support shall be installed prior to excavation of the subsequent round, consisting of:-

10 cm of shotcrete lining; 1 layer of wire mesh (100 x I00 mm. 4 kg/m2) to be fixed to the rock surface: Swellex (or similar) or SN bolting with 3 m lengths. 3 no. every first round and 4 no. every second round at locations required by the discontinuity pattern. Emergency Exit Tunnel Support Class 2 (EET S C 2)

8.2.15.2

Excavation canied out in jointed rock mass by drill and blast by means of smooth blasting of the full face with lengths of rounds between 1.7 and 2.2 metres. For each round, tunnel support shall be installed prior to excavation of the subsequent round, consisting of:-

-

15 cm of shotcrete lining; 1 layer of wire mesh (100 x 100 mm. 4 kg/m2), absence of steel rib for fixing of the wire mesh every second round to be considered: Lattice girder steel ribs (70/20130) every second round for profile control; A systematic S N rock bolt pattern with 3 m lengths, 6 no. every round with orientations required by the discontinuity pattern.Emergency Exit Tunnel Support Class 3 WET S C 3)

8.2.153

Excavation carried out in weak fractured rock mass by drill and blast by means of smooth blasting of the full face with lengths of rounds between 1.3 and 1.7 metres. For each round, tunnel support shall be installed prior to excavation of the subsequent round. consisting of:-

-

20 cm of shotcrete lining: 1 layer of wire mesh (100 x 100 mm, 4 kg/m2) with steel rib for fixing of the wire mesh; Lattice girder steel ribs (70120130) every round; 17 forepoling bars, 4m length; A shotcrete sealing of the tunnel face with 3 cm of shotcrete; A systematic S N rock bolt pattern with 3 m lengths, 6 no. per round, with orientations required by the discontinuity pattern. Emergency Exit Tunnel Support Class 4 (EET S C 4)

8.2.15.4

Excavation carried out in fault zone material andlor weathered rock mass by drill and blast by means of loosening shots andlor tunnel excavator in subdivided excavation steps with lengths of rounds between I .O and 1.3 metres. The tunnel face shall be opened in subdivisions and immediately sealed with 5 cm of shotcrete prior to the opening of the next subdivision. For each round. tunnel suppon shall be installed prior to excavation of the subsequent round, consisting of: x 100 mm. 4 kglm2) with steel rib for fixing of the wi 122132) every round:

Dagachhu HPP



-

21 forepoling bars 3m length (for the next round): A systematic SN rock bolt pattern with 4 m lengths. 9 no. every first round and 10 no. every second round, with orientations required by the discontinuity pattern; An invert arch supported with 20 cm of shotcrete and 1 layer of wire mesh (100 x 100 mm. 4 kglm2) with steel rib for fixing of the wire mesh.

The sensitivity of the rock mass to water requires particular care: Water shall be kept away from exposed rock surfaces by suitable means approved by the Employer. Ponding water shall not be allowed. 8.2.15.5 Emergency Exit Tunnel Support Class L (EET S C L)

Excavation in loose ground by means a tunnel excavator in subdivided excavation steps with lengths of rounds between 1.0 and 1.3 metres. The tunnel face of the pilot holelbench shall be opened in subdivisions and immediately sealed with 5 cm of shotcrete prior to the opening of the next subdivision. For each round, tunnel support shall be installed prior to excavation of the subsequent round, consisting of: 25 cm of shotcrete lining; 2 Layers of wire mesh (100 x 100 mm, 4 kg/m2) with steel rib for fixing of the wire mesh; Lattice girder steel ribs (95122132) every round; Either 38 driven forepoling bars of 3m length (for the next round), 38 forepoling pipes without mortar of 3rn length or 38 forepoling bars without mortar of 4m length: A rock bolt pattern of self drilling bolts with 4 m lengths, 5 no. every round in the sidewalls; An invert arch supported with 20 cm of shotcrete and 1 layer of wire mesh (100 x 100 mm, 4 kglm2) with steel rib for fixing of the wire mesh, installed at distances not exceeding 6m from the tunnel face. The sensitivity of the ground to water requires particular care. 8.2.16 8.2.16.1 Excavation a n d support of the Tailrace Tunnel Branch 1(TRI) Tailrace Tunnel Branch 1 Support Class 1(TR1 S C 1)

Excavation carried out in competent rock mass by drill and blast by means of smooth blasting of the full face with lengths of rounds between 2.2 and 3.0 metres. For each round, tunnel support shall be installed prior to excavation of the subsequent round, consisting of: 10 cm of shotcrete lining; 1 layer of wire mesh (100 x 100 mm, 4 kglm2) to be fixed to the rock surface; Swellex (or similar) or SN bolting with 3 m lengths, 3 no. every first round and 4 no. every second round at locations required by the discontinuity pattern. 8.2.16.2 Tailrace Tunnel Branch 1Support Class 2 ( T R l S C 2)

Excavation carried out in jointed rock mass by drill and blast by means of smooth blasting of the full face with lengths of rounds between 1.7 and 2.2 metres. For each round, tunnel support shall be installed prior to excavation of the subsequent round, consisting of: 15 cm of shotcrete lining: I layer of wire mesh (100 x 100 mm, 4 kglm2), absence of steel rib for fixing of the wire mesh every second round to be considered; Lattice girder steel ribs (70120130) every second round for profile control: A systematic S S rock bolt pattern with 3 m lengths, 6 no. every round with orientations required by the discontinuity pattern.

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Dagachhu HPP


6.2 Technical Specifications Chapter Oh Underground Excavation - 63 of 71

8.2.16.3

Tailrace Tunnel Branch 1Support Class 3 (TR1 S C 3)

Excavation carried out in weak fractured rock mass by drill and blast by means of smooth blasting of the full face with lengths of rounds between 1.3 and 1.7 metres. For each round, tunnel support shall be installed prior to excavation of the subsequent round. consisting of:-

-

20 cm of shotcrete lining: 1 layer of wire mesh (100 x 100 mm. 4 kglm2) with steel rib for fixing of the wire mesh; Lattice girder steel ribs (70120130) every round: 16 no. in every first round and 17 no. in every second round forepoling bars. 4m length: A shotcrete sealing of the tunnel face with 3 cm of shotcrete; A systematic SN rock bolt pattern with 3 m lengths, 6 no. per round, with orientations required by the discontinuity pattern. Tailrace Tunnel Branch 1 Support Class 4 (TR1 S C 4)

8.2.16.4

Excavation carried out in fault zone material and/or weathered rock mass by drill and blast by means of loosening shots andlor tunnel excavator in subdivided excavation steps with lengths of rounds between I .0 and 1.3 metres. The tunnel face shall be opened in subdivisions and immediately sealed with 5 cm of shotcrete prior to the opening of the next subdivision. For each round, tunnel support shall be installed prior to excavation of the subsequent round. consisting of:-

-

25 cm of shotcrete lining; 2 layers of wire mesh (100 x 100 mm. 4 kglm2) with steel rib for fixing of the wire mesh: Lattice girder steel ribs (95122132) every round; 20 no. in every first round and 21 no. in every second round forepoling b a n 3m length (for the next round); A systematic S N rock bolt pattern with 4 m lengths, 9 no. every round with orientations required by the discontinuity pattern; An invert arch supported with 20 cm of shotcrete and 1 layer of wire mesh (100 x 100 mm, 4 kglm2) with steel rib for fixing of the wire mesh.

The sensitivity of the rock mass to water requires particular care: Water shall be kept away from exposed rock surfaces by suitable means approved by the Employer. Ponding water shall not be allowed. 8.2.16.5 Tailrace Tunnel Branch 1 Support Class L (TR1 SC L)

Excavation in loose groundby means a tunnel excavator in subdivided excavation steps with lengths of rounds between 1.0 and 1.3 metres. The tunnel face of the pilot holeibench shall be opened in subdivisions and immediately sealed with 5 cm of shotcrete prior to the opening of the next subdivision. For each round, tunnel support shall be installed prior to excavation of the subsequent round, consisting of:-

-

25 cm of shotcrete lining; 2 Layers of wire mesh (100 x 100 mm, 4 kglm2) with steel rib for fixing of the wire m e s h Lattice girder steel ribs (95122132) every round; Either 37 driven forepoling bars of 3m length (for the next round). 37 forepoling pipes without mortar of 3m length or 37 forepoling bars without mortar of 4m length: A rock bolt pattern of self drilling bolts with 4 m lengths, 5 no. every round in the sidewalls; An invert arch supported with 2 0 c m of shotcrete and 1 layer of wire mesh (100 x 100 mm. 4 kglm2) with steel rib for fixing of the wire mesh. installed at distances not exceeding 6m from the tunnel face.

The sensitivity of the ground to water requires particular care.

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Dagachhu HPP


6.2 Technical Spsificationc Chapter 06 Underground Excavation - 65 of 71

An invert arch supported with 20 cm of shotcrete and 1 layer of wire mesh (100 x 100 mm. 4 kglm2) with steel rib for fixing of the wire mesh. The sensitivity of the rock mass to water requires particular care: Water shall be kept away from exposed rock surfaces by suitable means approved by the Employer. Ponding water shall not be allowed. 8.2.175 Tailrace Tunnel Branch 2 Support Class L (TR2 SC L)

Excavation in loose ground by means a tunnel excavator in subdivided excavation steps with lengths of rounds between 1.0 and 1.3 metres. The tunnel face of the pilot holebench shall be opened in subdivisions and immediately sealed with 5 cm of shotcrete prior to the opening of the next subdivision. For each round, tunnel support shall be installed prior to excavation of the subsequent round, consisting of: 25 cm of shotcrete lining; 2 Layers of wire mesh (I00 x I00 mm. 4 kglm2) with steel rib for fixing of the wire mesh: Lattice girder steel ribs (95122132) every round; Either 37 driven forepoling bars of 3m length (for the next round), 37 forepoling pipes without mortar of 3m length or 37 forepoling bars without mortar of 4m length; A rock bolt pattem of self drilling bolts with 4 m lengths, 5 no. every round in the sidewalls; An invert arch supported with 20 cm of shotcrete and 1 layer of wire mesh (100 x 100 mm. 4 kgIm2) with steel rib for fixing of the wire mesh, installed at distances not exceeding 6m from the tunnel face. The sensitivity of the ground to water requires particular care. 8.2.18 8.2.18.1 Excavation and support of the Tailrace Tunnel (TRT) Tailrace Tunnel Support Class 1(TRT S C 1)

Excavation carried out in competent rock mass by drill and blast by means of smooth blasting of the full face with lengths of rounds between 2.2 and 3.0 metres. For each round, tunnel support shall be installed prior to excavation of the subsequent round, consisting of:-

10 cm of shotcrete lining: 1 layer of wire mesh (100 x 100 mm, 4 kglm*) to be fixed to the rock surface; Swellex (or similar) or SN bolting with 3 m lengths, 4 no. every round at locations required by the discontinuity pattern. Tailrace Tunnel Support Class 2 (TRT SC 2)

8.2.18.2

Excavation carried out in jointed rock mass by drill and blast by means of smooth blasting of the full face with lengths of rounds between 1.7 and 2.2 metres. For each round, tunnel support shall be installed prior to excavation of the subsequent round, consisting of:-

15 cm of shotcrete lining; 1 layer of wire mesh (100 x 100 mm. 4 kglm2). absence of steel rib for fixing of the wire mesh every second round to be considered; Lattice girder steel ribs (70/20130) every second round for profile control; A systematic SN rock bolt pattern with 3 m lengths, 7 no. every round with orientations required by the discontinuity pattem. Tailrace Tunnel Support Class 3 (TRT S C 3)

8.2.183

Excavation carried out in weak fractured rock mass by drill and blast by means of smooth blasting of the full face with lengths of rounds between 1.3 and 1.7 metres. ~nsisting of:

4

.Dagachhu HPP Section 6 -Employer's Requzrernenrs-

*


20 cm of shotcrete lining; I layer of wire mesh (I00 x 100 mm. 4 kglm2) with steel rib for fixing of the wire mesh; Lattice girder steel ribs (70120130) every round; 20 no. in every first round and 21 no. in every second round forepoling bars, 4rn length; A shotcrete sealing of the tunnel face with 3 cm of shotcrete; A systematic SN rock bolt pattern with 3 m lengths. 7 no. per round, with orientations required by the discontinuity pattern. Tailrace Tunnel Support Class 4 ( T R T S C 4)

8.2.18.4

Excavation carried out in fault zone material and/or weathered rock mass by drill and blast by means of loosening shots andlor tunnel excavator in subdivided excavation steps with lengths of rounds between 1.0 and 1.3 metres. The tunnel face shall be opened in subdivisions and immediately sealed with 5 cm of shotcrete prior to the opening of the next subdivision. For each round, tunnel support shall be installed prior to excavation of the subsequent round, consisting of. 25 cm of shotcrete lining; 2 layers of wire mesh (100 x 100 mm, 4 kglmz) with steel rib for fixing of the wire mesh; Lattice girder steel ribs (95122132) every round; 25 no. in every first round and 26 no. in every second round forepoling bars 3m length (for the next round); A systematic SN rock bolt pattern with 4 m lengths, 11 no. every round with orientations required by the discontinuity pattern; An invert arch supported with 20 cm of shotcrete and I layer of wire mesh (100 x 100 mm, 4 kglmz) with steel rib for fixing of the wire mesh. The sensitivity of the rock mass to water requires particular care: Water shall be kept away from exposed rock surfaces by suitable means approved by the Employer. Ponding water shall not be allowed. 8.2.18.5 Tailrace Tunnel Support Class L (TRTS C L)

Excavation in loose ground by means a tunnel excavator in subdivided excavation steps with lengths of rounds between 1.0 and 1.3 metres. The tunnel face of the pilot holebench shall be opened in subdivisions and immediately sealed with 5 cm of shotcrete prior to the opening of the next subdivision. For each round. tunnel support shall be installed prior to excavation of the subsequent round. consisting of: 25 cm of shotcrete lining; 2 Layers of wire mesh (100 x 100 mm, 4 kglmz) with steel rib for fixing of the wire mesh: Lattice girder steel ribs (95/22/32) every round; Either 46 driven forepoling bars of 3m length (for the next round), 46 forepoling pipes without mortar of 3rn length or 4 6 forepoling bars without mortar of 4m length; A rock bolt pattern of self drilling bolts with 4 m lengths, 6 no. every round in the sidewalls; An invert arch supported with 20 cm of shotcrete and 1 layer of wire mesh (100 x 100 mm, 4 kg/mz) with steel rib for tixing of the wire mesh, installed at distances not exceeding 6m from the tunnel face. The sensitivity of the ground to water requires particular care. 8.2.19 8.2.19.1 Excavation a n d support of Auxiliary Adit 1(AUI) Auxiliary Adit 1Support Class 1 (AUI S C 1)

Excavation carried out in competent rock mass by drill and blast by means of smooth blasting of the full face with lengths of rounds between 2.2 and 3.0 metres.

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Documents

VOLUME-3 TECHNICAL SPECIFICATION AND GEOLOGICAL REPORT PART-1