DASU HYDROPOWER PROJECT (MW-01)Care and handling of water works and Quantification of Lump sum Items

Technical Services Group Design Criteria Results

Item No Work Description as per BOQ Anticipated works to be performed Component Composition Status

1 B1-1 Dewatering of Construction Site- Diversion Tunnel Access, clearing, construction of dyke, subsurface dewatering

Inlet area dyke 5 5 CompletedOutlet area dyke Not StartedSubsurface dewatering inlet portal In progress

Subsurface dewatering outlet portal Not Started

Dewatering along the diversion tunnel In progress

2 B-2Construction of upstream dewatering dyke- Upstream starter dam

Access, clearing, construction of dyke Construction of dyke Completed

6 B2-5

Sealing wall for river deposit material- Upstream Starter Dam Dilling, double packer grouting, column jet groutingDouble Packer Grouting for lower deposit Completed

Column Jet Grouting for upper deposit Completed

8 B3-1 Access, clearing, construction of dyke, dewatering Construction of dyke Completed9 C-2 Dewatering of construction site- Main Dam Surface dewatering, Subsurface dewatering Subsurface dewatering Completed10 D-2 Dewatering of construction site- Plunge Pool Surface dewatering, Subsurface dewatering Subsurface dewatering Completed

11 F-1Surface dewatering, Subsurface dewatering Left Flushing Tunnel Subsurface dewatering Not StartedSurface dewatering, Subsurface dewatering Right Flushing Tunnel Subsurface dewatering Not Started

13 F-2Dewatering of construction site- Gate Chamber Subsurfae Dewatering Left Gate Chamber Subsurface dewatering Completed

Subsurfae Dewatering Right Gate Chamber Subsurface dewatering Completed

15 F-3Surface dewatering, Subsurface dewatering Left Flushing Tunnel Subsurface dewatering Not StartedSurface dewatering, Subsurface dewatering Right Flushing Tunnel Subsurface dewatering Not Started

17 H-1Dewatering of construction site- Permanent Access Road LD

Surface dewatering Surface dewatering Once in 2 year rainfall Completed

18 H-2Dewatering of construction site- Permanent Access Road RD

Surface dewatering Surface dewatering Completed

19 H-3Dewatering of construction site- Permanent Access Road RU

Surface dewatering Surface dewatering Completed20 H-4 Dewatering of construction site- Spoil Bank Surface dewatering Surface dewatering Not Started

22Dewatering of construction site- Upstream Starter Dam

Subsurface dewatering Completed

Note: Highlighted Items are not in BOQThe idea to control ground water seepage is to install the

Various method that can be used for handling subsurface water during construction are:Sump and ditchesDeep WellsWell pointsGround FreezingEductorsCutoff Walls i.e. grout curtains, slurry walls, concrete walls

Design Flood RP (Yrs)

Source of Seepage (river/ Stream/ Lake)

Type of Flow (Artesian/ gravity)

Crest Elevation (EL.)

Dewatering Method

Dewatering effort/ Number of Pumps

Construction of dewatering dyke for downstream starter dam and cofferdam

Dewatering of construction site- Flushing Tunnel Inlet Portal and Upstream portion

Dewatering of construction site- Flushing Tunnel Outlet Portal and downstream portion

Not included in BOQ

Subsurface dewatering during pouring of Matt foundation

Deep Well Dewatering System Deep wells can be used to dewater pervious sand or rock formations or to relieve artesian pressure beneath an excavation. They are particularly suited for dewatering large excavations requiring high rates of pumping, and for dewatering deep excavations for dams, tunnels, locks, powerhouses, and shafts. Excavations and shafts as deep as 300 feet can be dewatered by pumping from deep wells with turbine or submersible pumps. The principal advantages of deep wells arethat they can be installed around the periphery of an excavation and thus leave the construction area unemcumbered by dewatering equipment, as shown in figure2-7, and the excavation can be predrained for its full depth.b. Deep wells for dewatering are similar in type and construction to commercial water wells. They commonly have a screen with a diameter of 6 to 24 inches with lengths up to 300 feet and are generally installed with a filter around the screen to prevent the infiltration of foundation materials into the well and to improve the yield of the well.c. Deep wells may be used in conjunction with a vacuum system to dewater small, deep excavations for tunnels, shafts, or caissons sunk in relatively finegrained or stratified pervious soils or rock below the groundwater table. The addition of a vacuum to the well screen and filter will increase the hydraulic gradient to the well and will create a vacuum within the surrounding soil that will prevent or minimize seepage from perched water into the excavation. Installations of this type, as shown in figure 2-8, require adequate vacuum capacity to ensure efficient operations of thesystem.

Wells for temporary dewatering and permanent drainage systems may have diameters ranging from 4 to 18 inches with a screen 20 to 75 feet long depending on the flow and pump size requirements.(1) Well screens. Screens generally used for dewatering wells are slotted (or perforated) steel pipe, perforated steel pipe wrapped with galvanized wire, galvanized wire wrapped and welded to longitudinal rods, and slotted polyvinyl chloride (PVC) pipe. Riser pipes for most dewatering wells consist of steel or PVC pipe. Screens and riser for permanent wells are usually made of stainless steel or PVC. Good practice dictates the use of a filter around dewatering wells, which permits the use of fairly large slots or perforations, usually 0.025 to 0.100 inch in size. The slots in well screensshould be as wide as possible but should meet criteria given in c below.(2) Open screen area. The open area of a well screen should be sufficient to keep the entrance velocity for the design flow low to reduce head losses and to minimize incrustation of the well screen in certain types of water. For temporary dewatering wells installed in nonincrusting groundwater, the entrance velocity should not exceed about 0.15 to 0.20 foot per second; for incrusting groundwater, the entrance velocity should not exceed 0.10 to 0.20 foot per second.For permanent drainage wells, the entrance velocity should not exceed about 0.10 foot per second. As the flow to and length of a well screen is usually dictated by the characteristics of the aquifer and drawdown requirements, the required open screen area can be obtainedby using a screen of appropriate diameter with a maximum amount of open screen area.(3) Well hydraulics. Head losses within the well system discussed in paragraph 4-2a(5) can be estimated from figure 4-24.c. Filters. Filters are usually 3 to 5 inches thick for wellpoints and 6 to 8 inches thick for large-diameter wells (fig. 4-30). To prevent infiltration of the aquifer materials into the filter and of filter materials into thewell or wellpoint, without excessive head losses, filters should meet the following criteria: Screen-filter criteriaFilter-aquifer criteriaMax filter D15 Max filter D50Min aquifer D85 Min aquifer D50Min filter D15Max aquifer D15If the filter is to be tremied in around the screen for awell or wellpoint, it may be either uniformly or ratherwidely graded; however, if the filter is not tremiedinto place, it should be quite uniformly graded (D90/D10continuous stream to minimize segregation.Effective well radius. The

“effective” radius rw of a well is that well radius which would have no hydraulic entrance loss Hw. If well entrance losses are considered separately in the design of a well or system of wells, rw for a well or wellpoint without a filter may be considered to be one-half the outside diameter of the well screens; where a filter has been placed around a wellpoint or well screen, rw may generally be considered to be one-half the outside diameter or theradius of the filter.Well penetration. In a stratified aquifer, the effective well penetration usually differs from that computed from the ratio of the length of well screen to totalthickness of the aquifer. A method for determining the required length of well screen W to achieve an effective penetration W in a stratified aquifer is given in appendix E.f. Screen length, penetration, and diameter. The length and penetration of the screen depends on the thickness and stratification of the strata to be dewatered (para 4-2a(6)). The length and diameter of the screen and the area of perforations should be sufficientto permit the inflow of water without exceeding the entrance velocity given in b(2) above. The “wetted screen length hws” (or hw for each stratum to be dewatered) is equal to or greater than Qw/qc (para 4-2a(4) and (6)). The diameter of the well screen should be at least 3 to 4 inches larger than the pump bowl or motor.

Care and Hanlding of Water:Item No. River Diversion TunnelSpecification No 212

Diversion Structure :Name U/S Dewatering DykeCore Composition Rockfill/ Gravel and Sand Impermiable Layer Clay LayerBed Level 765.0m AMSLDesign Water Level 772.0m AMSLCrest Level 773.0m AMSLFreeboard 1.0mDesign RP NADesign Discharge 500 ( page #2, Volume 3(a) SPECIFICATIONS [Part 2 of 3], CIVIL WORKS TECHNICAL SPECIFICATIONS

U/S dewatering dyke shall mean the rockfill sand and gravel embankment with surface soil impervious coating whose detailed design shall be prepared by the Contractor to be provided downstream (d/s) of the diversion tunnel inlet.

U/S dewatering dyke shall mean the rockfill sand and gravel embankment with surface soil impervious coating whose detailed design shall be prepared by the Contractor to be provided downstream (d/s) of the diversion tunnel inlet.

sm /3

( page #2, Volume 3(a) SPECIFICATIONS [Part 2 of 3], CIVIL WORKS TECHNICAL SPECIFICATIONS

U/S dewatering dyke shall mean the rockfill sand and gravel embankment with surface soil impervious coating whose detailed design shall be prepared by the Contractor to be provided downstream (d/s) of the diversion tunnel inlet.

U/S dewatering dyke shall mean the rockfill sand and gravel embankment with surface soil impervious coating whose detailed design shall be prepared by the Contractor to be provided downstream (d/s) of the

U/S dewatering dyke shall mean the rockfill sand and gravel embankment with surface soil impervious coating whose detailed design shall be prepared by the Contractor to be provided downstream (d/s) of the diversion tunnel inlet.

Care and Hanlding of Water:Item No. River Diversion TunnelSpecification No 212

Diversion Structure :Name D/S Dewatering DykeCore Composition Rockfill/ Gravel and Sand Impermiable Layer Clay LayerBed Level 755.0m AMSLDesign Water Level 772.0m AMSLCrest Level 773.0m AMSLFreeboard 1.0mDesign RP NA Design Discharge 500 ( page #2, Volume 3(a) SPECIFICATIONS [Part 2 of 3], CIVIL WORKS TECHNICAL SPECIFICATIONS

D/S dewatering dyke shall mean the rockfill sand and gravel embankment with surface soil impervious coating whose detailed design shall be prepared by the Contractor to be provided downstream (u/s) of the diversion tunnel outlet.

sm /3

( page #2, Volume 3(a) SPECIFICATIONS [Part 2 of 3], CIVIL WORKS TECHNICAL SPECIFICATIONS

D/S dewatering dyke shall mean the rockfill sand and gravel embankment with surface soil impervious coating whose detailed design shall be prepared by the Contractor to be provided downstream (u/s) of the

U/S Strater Dam Sealing Wall:Sealing wall must be built under foundation concrete to stop water seepage from step of EL 780m.Column Jet Grount:Column Jet Grount Depth 20.00 mDiameter 1.80 mNumber of Holes 61.00Number of Rows 2.00 rowsTop Elevation 760.00 m ASML

Double Packer GroutDouble Packer Grout depth 30.53 mSpacing 1.20 mNumber of Rows 3.00 rowsDiameter mTop Elevation 740.00 m ASML

Original riverbed 764.00 m ASMLRCC Mat Elevation 768.00 m ASML

Starter Dam must be built on rock foundation except riverbed material.Upstream surface of cofferdam is covered by Shotcrete (thicness is 100mm).River deposit will be excavated and replaced by CVC for 4 m depth Specified strength of CVC is larger than 32 MPa.

Contraction joints are built in evc and RCe at section A to FSealing Wall must be built under foundation concrete to stop water seepage from step of EL.780m.Drilled hole for Sealing Wall in Hardfil! dam, Ree mat and Replaced CVC must be filled after completion of Sealing Wall.

RCC mat of 4 m depth wi!! be built under hardfitl dam.Specified strength of Rce is larger than 15 MPa.

U/S Strater Dam

Sealing wall must be built under foundation concrete to stop water seepage from step of EL 780m.

River deposit will be excavated and replaced by CVC for 4 m depth Specified strength of CVC is larger than 32 MPa.

Sealing Wall must be built under foundation concrete to stop water seepage from step of EL.780m.Drilled hole for Sealing Wall in Hardfil! dam, Ree mat and Replaced CVC must be filled after completion of Sealing Wall.

Main Dam Specification No 211Natural surface level EL. 765 mGround water table level EL. 765 mFoundation Level EL. 715 mBottom of Strainer EL. 695 mDewatering Area 28000 m2

Bore Holes : DL-6, D5L-01, DL-5, D5R-08, DR-5, D5R-01, DR-6

Main Dam

Plunge PoolSpecification No 211Natural surface level EL. 761 mGround water table level EL. 761 mFoundation Level EL. 710 mBottom of Strainer EL. 690 mDewatering Area 11250 m2

Bore Holes : DL-6, D5L-01, DL-5, D5R-08, DR-5, D5R-01, DR-6

Plunge Pool

Gate ChamberSpecification No 211Left Flushing Tunnel Gate Chamberlength of access tunnel 340GWT EL. 825

Left Flushing Tunnel Gate Chamberlength of access tunnel 200GWT EL. 860

Gate Chamber

LD1 No GWT encounteredLD2 No GWT encounteredLD3 No GWT encounteredLD4 No GWT encountered

LD6 No GWT encountered

LD9 No GWT encounteredRU1 No GWT encountered

RU2 No GWT encounteredRU3 No GWT encountered

RD1 No GWT encountered

RD2 No GWT encountered

RD3 No GWT encounteredRD6 No GWT encounteredSpoil Bank Location not clear

Permanent Access Roads

Requirement for subsurface dewatering

Requirement for river protection dyke Requirement for Nullah crossingAbove 5 year return period flood Not requiredAbove 5 year return period flood Not requiredAbove 5 year return period flood Not requiredAbove 5 year return period flood Not required

Above 5 year return period flood

Above 5 year return period floodAbove 5 year return period flood Not required

Above 5 year return period flood 1 causeway is included as part of permanent worksAbove 5 year return period flood

Above 5 year return period flood

Above 5 year return period flood

Above 5 year return period floodAbove 5 year return period flood Not required

Location not clear

2 causeways is included as part of permanent works 1 Box culvert included

2 Box culverts 1m x 3m size included as permanent works

1 causeway is included as part of permanent works 1 Box culvert included

1 causeway is included as part of permanent works 1 Box culvert included

1 causeway is included as part of permanent works 1 Box culvert included

Remarks