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Embankment Fill

By Bruce Knight,2014-04-29 17:56
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method statement for embankment fill

    BAKUN HYDROELECTRIC PROJECT Section 1.0 Embankment Work Plan PACKAGE CW2 MAIN CIVIL WORKS

    T a b l e o f C o n t e n t s

    1.0 EMBANKMENT WORK PLAN……………………………………………………… 1

    1.1 Construction Of The Concrete Face Rockfill Dam (CFRD)………………………… 1

    1.1.1 General………………………………………………………………………………. 1 1.1.2 General Construction Program……………………………………………………. 3 1.1.3 River Diversion, Flood Control And Their Method Statements………….. 4

    A) River Diversion Features……………………………………………………. 4

    B) Standards And Phasing Of River Diversion ……………………………….. 4

    C) Arrangement And Construction Of Diversion And Closure Structures………….. 5

    D) Construction Equipment………………………………………………………….. 9

    E) Dewatering Of The Foundation Pit ……………………………………………... 9

    F) Downstream Cofferdam Removal And Cleaning……………………………….. 11

    1.1.4 Excavation And Treatment Of Dam And Plinth Foundations………………….. 11

    A) Excavation Procedures And Access …………………………………………….. 12

     B) Technology And Methods Of Excavation………………………………………. 13

     C) Dam Foundation Treatment……………………………………………………... 16

     D) Contractor’s Plant And Manning For Excavation Of The Dam Foundation…….18

     E) Planning Of The Dam Foundation Excavation…………………………………. 20

    1.1.5 Dam Embankment………………………………………………………………… 21

     A) General………………………………………………………………………….. 21

     B) Planning Of Dam Embankment…………………………………………………. 22

     C) Planning And Exploitation Of Embankment Fills………………………………. 26

     D) Transportation Of Embankment Fills…………………………………………… 29

     E) Embankment Technology……………………………………………………….. 30

     F) Compaction Of Embankment Fills And Rolling Test…………………………… 33

     G) Rolling And Protection Of Cushion Slope Surfaces……………………………. 35

     H) Quality Inspection And Control Of Embankment……………………………….. 37

     I) Major Items Of The Contractor’s Plant And Manning For Embankment………. 38

1.1.6 Plinth And Face Slab Concrete Construction………………………………………

     39

     A) General………………………………………………………………………….. 39 MALAYSIA-CHINA HYDRO JOINT VENTURE Page 1 of 69

    BAKUN HYDROELECTRIC PROJECT Section 1.0 Embankment Work Plan PACKAGE CW2 MAIN CIVIL WORKS

     B) Plinth Construction……………………………………………………………… 40

     C) Face Slab Concrete Construction……………………………………………….. 42

     D) Construction Joint Treatment…………………………………………………… 46

     E) Face Slab Concrete Curing……………………………………………………… 47

     F) Construction In Special Weather ……………………………………………….. 47

    G) Anticorrosive Concrete Construction……………………………………………. 48

T a b l e o f C o n t e n t s (cont’d)

     H) Water Stops for Face Slab Joint …………….………………………………… 49

     I) Construction Of Parapet Concrete……………………………………………… 49

     K) Construction Equipment And Manpower Arrangement……………………….. 50

    1.1.7 Foundation Consolidation Grouting And Curtain Grouting………………….. 51

     A) Construction Features………………………………………………………….. 51

     B) Construction Principles………………………………………………………… 52

     C) Treatment Method On Special Geological Section……………………………. 52

     D) Arrangement Of Drilling And Grouting Works……………………………….. 53

     E) Grout Tests And Materials…………………………………………………….. 53

     F) Execution Of Grouting Works………………………………………………… 55

     G) Inspection Of Grouting………………………………………………………… 63

     H) Taking Over Upon Completion……………………………………………….. 64

     I) Major Equipment……………………………………………………………… 65

1.0 EMBANKMENT WORK PLAN

1.1 Construction Of The Concrete Face Rockfill Dam

    1.1.1 General

    The hydroelectric station of the Bakun Project will be located on the Balui River in

    Sarawak, Malaysia, about 37 kilometers upstream of Belaga. The multipurpose

    structure is composed of a concrete face rockfill dam, a spillway on the left bank,

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    BAKUN HYDROELECTRIC PROJECT Section 1.0 Embankment Work Plan

    PACKAGE CW2 MAIN CIVIL WORKS

power conduits, a powerhouse and etc. The dam will be 205m high, 740m long and

    12m wide at its crest, and 574m wide at its foundation; its parapet wall will be 236.5m

    ASL; its normal impounding level will be 228m ASL and the minimum operating

    water level 195m ASL.

The dam will be Zoned as follows: -

    Zone 1A: Selected impervious earth fill

    Zone 1B: Random earth fill

    Zone 2A: Fine filter Zone (processed fresh greywacke)

    Zone 2B: Coarse transition Zone (processed fresh greywacke)

    Zone 3A: Rockfill (fresh greywacke), 0.3m max. particle size

    Zone 3B: Rockfill (fresh greywacke)

    Zone 3C: Rockfill (greywacke or mudstone or mixture)

    Zone 3D: Rockfill (coarse fresh greywacke)

The total quantity of dam embankment will be 15,400,000m3, as broken down for

    each Zone in the Table 1.1.1-1. The earth and rock excavation of the foundation will

    be 1,408,000m3, plinth concrete 9,800m3, face concrete 59,400m3, and the drilling

    length of foundation grouting 126,211m.

    Zoned Embankment Quantities

    Table 1.1.1-1

    3 Unit: 1,000m

Zone 1A 1B 2A 2B 3A 3B 3C 3D

    40.5 299.7 5.2 269.6 475.2 6,840.3 5,815.2 1,654.7 Quantity

The valley at the dam site is gorge-like with rather steep slopes and its narrowest

    section is only about 40m wide. The bedrock is composed of greywacke strata, which

    alternate with mudstone/shale intercalations and inter-bedded shale/mudstone and

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BAKUN HYDROELECTRIC PROJECT Section 1.0 Embankment Work Plan

    PACKAGE CW2 MAIN CIVIL WORKS

    greywacke beds. The plinth foundation will mainly seat in the greywacke belt, and

    there are a few inter-beddings of greywacke and shales in the riverbed. The area of the

    dam site has not any major fractured belt, and its structural formations are mostly

    joints, crevices and beddings. The weathered depth of rocks is 10~15m at the riverbed,

    15~20m on slopes, and 60~70m at faults.

    1.1.2 General Construction Program

     General Construction Flow Chart

Raising of auxiliary upstream

    cofferdam

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    BAKUN HYDROELECTRIC PROJECT Section 1.0 Embankment Work Plan PACKAGE CW2 MAIN CIVIL WORKS

    Construction preparation

    Foundation exc. & treatment on slopes Construction of downstream cofferdam

    Foundation exc. & treatment in riverbed

    st1 phase plinth concrete

    1st phase consolidation grouting at plinth foundation

    Embankment of Integrated Cofferdam

    2nd phase plinth concrete

    st1 phase curtain grouting II phase dam embankment

    ndst2 phase consolidation grouting at plinth foundation 1 phase face concrete

    nd2 phase curtain grouting III phase dam embankment nd2 phase face concrete

    rd3 phase face concrete

    Construction of parapet wall

    IV phase dam embankment

    Dam crest pavement

    Completion

    1.1.3 River Diversion, Flood Control And Their Method Statements

    A) River Diversion Features

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    According to hydro meteorological data from Bakun area, there is abundant rainfall in the dam area, with a long-term annual average rainfall of 4,500mm distributed throughout the year. The wet season corresponds to the period of October to May of the next year and the dry season corresponds to the period of June to September.

    The river diversion work consists of river diversion tunnels and the upstream and downstream cofferdams, and is planned in such a way that river closure at riverbed will be achieved at a single time, with river water being diverted through diversion tunnels till the reservoir is completed, when the impounding starts, one of the diversion tunnels will be converted to the release water outlet while the other two plugged. The three diversion tunnels arranged on the right bank and the upstream cofferdam have already been completed by others and put into service. The designed elevation of the upstream cofferdam is 98m ASL and able to withstand floods of 20-year return, while the downstream cofferdam is designed as contiguous steel pipe piles, with a weir crest of 64.5m ASL, and able to withstand floods of a 500-year return.

    Dam construction is on the critical path of Package CW2. In order to protect it, especially excavation and treatment of dam riverbed foundation, placement of riverbed plinth concrete and preliminary dam embankment, against impact of floods and sustain its continuity, the upstream cofferdam will be raised to have a higher flood protection level of 2%, (floods of 50-year return).

    According to data relevant to water levels and flow rates, the upstream cofferdam shall be raised to 105m ASL; and meanwhile, in consideration of the slow progress of the downstream cofferdam of steel pipe piles, a temporary retaining cofferdam with an inclined clay core will be constructed between the downstream cofferdam of contiguous steel pipe piles and the excavation area of dam foundation, to have a flood protection level of over 5% (floods of 20-year return), with a weir crest elevation of 62.8m.

B) Standards And Phasing Of River Diversion

    i. Standard and Method

    Pursuant to the construction program of this project, the standards

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    of river diversion will be: protection against floods of 50-year

    stfloods by the upstream cofferdam in the 1 phase and protection

    ndagainst floods of 500-year floods by the dam in the 2 phase.

    The method of river diversion is arranged in such a way that water

    will be retained by upstream, downstream and temporary

    cofferdams and discharged through diversion tunnels.

    ii. Phasing Of River Diversion

    According to the dam construction schedule, diversion for

    construction is divided into 2 phases:

    st1 phase from the commencement of works to July 2004: Water

    will be retained by the upstream cofferdam and downstream

    retaining cofferdam with an inclined clay core, and discharged

    through the diversion tunnels. Works to be concluded in this phase

    include dam foundation excavation, foundation treatment,

    stembankment of the Integrated Cofferdam, 1 phase face concrete

    placement; the Integrated Cofferdam will be filled to 121m ASL

    and ready for retaining of water; and the downstream cofferdam of

    contiguous steel pipe piles will be completed.

    nd2 phase from July 2004 to the impounding of the dam: In this

    phase, water will be retained by the Integrated Cofferdam together

    with the downstream cofferdam of contiguous steel pipe piles, and

    discharged through the diversion tunnels. Works to be completed in

    this phase include dam placement, face concrete placement,

    powerhouse and spillway.

C) Arrangement And Construction Of Diversion And Closure

    Structures

Diversion and closure structures include the diversion tunnels (completed),

    upstream cofferdam, downstream cofferdam (inclined clay core cofferdam

    and cofferdam of contiguous steel pipe piles) and the Integrated Cofferdam.

    Refer to the Construction Drawing No. CW2-C-MDB-1 of Volume 8.

    i. Raising Of Upstream Cofferdam

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    (Please refer to the Construction Drawing No. CW2-C-MDB-2 of Volume 8).

    The completed upstream cofferdam with a clay core has a weir crest elevation of 98m for discharge section and 104m for other than discharge section of river and weir crest width of 10m, with its flood protection level of 5% (floods of 20-year return). The raised cofferdam will have a weir crest elevation of 105m and a width of 10m. In light of the actual topography, raising and widening of the cofferdam will be executed from the upstream of the existing cofferdam, with a resultant upstream slope ratio of 1:2.25. This part of works represents a total fill quantity of

    3247,800m. The raised upstream section is shown in Drawing

    CW2-C-MDB-02.

    Cofferdam construction: Placement of the upstream cofferdam can be started after the commencement of works. Its fill material will directly come from excavation of the dam foundation or spillway. Soil material will come from stripping of Quarry II. Prior to the placement of the cofferdam, its surface will be treated with excavators; the fill materials will be hauled with dump trucks, spread with bulldozers and rolled where above water with vibrating rollers in layers, each of which shall be subject to 4 to 6 passes.

    ii. Temporary Downstream Cofferdam With An Inclined Clay

    Core

    This cofferdam is designed to have a weir crest width of 8m, length of 198m, elevation of 62.8m, and upstream to downstream slope of 1:2. The cofferdam will be filled with materials from excavation of dam foundation, with soil materials sourced from stripping of

    3Quarry II. The total fill quantity will be 13,460m. Drawing No.

    CW2-C-MDB-02 shows the type of cross sections.

    A branch of R1 on the right bank will be used for the construction of the cofferdam. River closure will be achieved with an earth and rock dyke by the vertical closure method. With river closure achieved, clay will be dumped towards to the downstream of the cofferdam in an advancing forward manner for seepage closure, and protected with ripraps at the downstream side against scouring of floods.

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    iii. Downstream Cofferdam Of Contiguous Steel Pipe Piles

    (Please refer to the Construction Drawing No. CW2-C-MDB-3 of

    Volume 8)

    This cofferdam will have a weir crest elevation of 64.5m, piling

    diameter of 30.6m and maximum height of 30m, and weir crest

    length of 208.18m; the pipe piles will be backfilled inside with

    sand and gravel, and the right bank connected to the bank slope

    with cast-in-situ concrete. For the avoidance of cofferdam seepage,

    the upstream side bottoms of the cofferdam will be covered with a

    cast-in-situ cover and treated with grouting as designed. The main

    quantity of the works for the downstream cofferdam is shown in

    Table 1.1.3-1.

    Table of Downstream Cofferdam Quantities

    Table 1.1.3-1

    Item Steel Piling Sand-gravel Concrete Removal of Sand-gravel Drilling Grouting

    Backfill Placement Steel Removal

    Pilings

    Unit t m33 M3 T m M M

    Quantity 2,450 117,000 2,300 2,450 117,000 1,350 200

    iv. Work Process

    According to the arrangement of roads in the Site, construction of

    steel pipe piles will progress from the right to the left bank. A

    shortcut will be built from the existing R1 (70.00m) on the right

    bank to the cofferdam top (64.50m), and then construction of the

    cofferdam will be carried out. The work process is: preparation ?

    right-bank concrete placement ? installation of piling frame ?

    assembly of pilings ? driving of pipe piles ? piling ?sand-gravel

    backfill ? removal of mould frames ? next cycles till completion

    of pipe piles ? upstream side concrete placement ? drilling ?

    grouting ? end.

    v. Construction Method

    Right-bank concrete placement: Steel gang forms will be shuttered

    for concrete placement. Right-bank pipe piles will be buried and

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    installed. Verification will be first conducted with high-precision surveying instruments, to ensure accuracy of the cofferdam axis. Concrete will be transported from the batching plant to the work site with truck mixers and tamped composite with immersion vibrators.

    Installation of piling frame: Mould frame will be in the same shape as the lattice and used to support temporarily pipe piles and as a working platform. It will be braced by anchor columns, which will be driven into the foundation with piling machine to firmly fix the frame. Accurate positioning will be required during installation, without any deviation; otherwise assembly of pipe piles will not be achieved.

    Sheet piling installation: Prior to any installation, pipe piles will be checked in respect of straightness, texture and fore-shaft pattern. Lifting will be carefully handled, to avoid potential deformation. Connecting pilings will be first installed, and fixed to the piling frame by spot welding or draglines. Pipe piles will be installed alternately from both sides of the lattice, to enable their concurrent completion, and kept stable before the closure of lattice. Driving of pilings: Driving of pilings will not be started until completion of assembly of all pipe piles in the same lattice and installation of 2-5 pipe piles in the adjacent lattice. It will be performed in stages, with 0.6-1.5m driving performed around the periphery each time until the ends of pipe piles reach the designed elevation. Pilings will be driven in pairs with double-acting pneumatic hammers. Application of light-duty hammers will precede that of medium-duty ones. In the event of great resistance and difficulty in driving of pilings, water jets or drilling may be applied.

    Sand-gravel backfill: With pipe piles in each lattice put in place, backfill will be immediately performed to avoid collapse or deformation. For the avoidance of difficulty in the installation of connecting pipe piles as a result of backfill expansion, some pilings will be installed in adjacent connecting sections. Backfill of connecting sections will be performed after that of adjacent circular lattices, to reach a height above that of the latter. Suitable backfill materials will be delivered by dump trucks to the end of cofferdam, conveyed by conveyor belts, and then manually leveled during backfill to prevent local piling up and subsequent

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