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- 21 (viii) Pipe lengths should never be deflected in the joint to any greater degreethan recommended by the manufacturer.(ix)(x)(xi)Pipe should have adequate support along their whole length or should bebedded, haunched or surrounded with concrete as per StandardDrawing WSD 1.1. The use of timber or other means to save formingsocket holes must not be permitted. All objects on or in the surface onwhich the pipe is to be laid which may cause damage to the pipe shouldbe removed.Pipelaying should follow closely upon the progress of trench excavation.All necessary precautions should be taken to prevent floatation of pipes.(xii) For pipelaying near deep sump gullies, it is necessary to ensure thatthere is adequate clearance between the pipeline and the drainageconnection. See Appendix 3.1 and HyD’s Technical Circular No. 3/90for details of the restricted zone around deep sump gullies.(xiii) When handling asbestos cement pipes, special precautionary measuresmust be taken in accordance with “Asbestos Work Manual forMaintenance of Asbestos Cement Water Pipes” regarding their cuttingand disposal.(xiv) For pipelaying in a new bridge the pipes should be located in a troughaccessible from above or supported on concrete/steel works cantileveredfrom the side of the bridge.(xv) When handling polyethylene pipes, special precautionary measuresshould be taken in accordance with “Design Guide for PolyethylenePipelines for Water Supply Purpose”.(xvi) When laying pipes in reclaimed areas or at locations that are susceptibleto differential settlement, special attention should be given to positionappropriate and sufficient flexible joints to prevent leakage or even pipeburst due to uneven settlement. Surrounding the pipes with concreteunder this condition must only be made with extreme care especially forsteel pipe with welded joints. In the event that ground settlement hasinduced sufficient stress to open up the welded joints, the surroundingconcrete will become an obstacle to the repair operation.3.6 Thrust BlocksThrust blocks prevent pipes from being moved by forces exerted within the
- 22 pipe arising from the internal pressure of the pipeline or the flow of waterhitting bends, tapers and closed or partially closed valves. The size of a thrustblock is dependent upon the deflection of the flow and the head of water insidethe pipe. Refer to “Guidance Note on the Design of Thrust Blocks forBuried Pipelines” in designing thrust blocks. Typical details of thrust blocks,including horizontal and vertical bend blocks, tee block, taper block and endblock, are shown in Standard Drawing WSD 1.4.(i)For Flexibly Joined PipesThrust blocks are essential on flexibly joined pipelines where any pipemovement would open up the joints in the line and cause water leakage.They should be provided to all bends, branches and tapers and pipe endsto take the full thrust unless special design is provided. However, theyshould not rely on lateral soil pressure for their stability because in HongKong situation, there is a high risk that the soil is removed by otherparties without notifying WSD.(ii)For Steel Pipes with Welded JointsFor buried steel pipes of diameter 1200 mm and under and subject to aworking head of less than 100 m, there is no need to provide any thrustblocks for bends of less than 45 o . For bends of 45 o and greater, it issufficient to design thrust blocks to resist 50% of the thrust. However,in both cases, there must be no loose joint (such as bolted collars orthose joints normally used for valve installations) within 30 m on eitherside of the bend; otherwise the full thrust must be resisted by thrustblocks.Unless it is known that the full thrust is being resisted by a thrust block,repairs, connections and branches to an existing steel main within 30mfrom a bend, if unavoidable, should be effected without introducing aloose joint (e.g. by using welded collars or harnessed couplings).Similarly valves should not be inserted within this distance unlessharnessed flange adaptors are used or additional thrust blocks areprovided to take the full thrust.For steel pipes of diameter larger than 1200 mm or for pipes subject tomore than 100 m working head, design of thrust blocks needs individualconsideration to provide a higher safety factor. Thrust blocks must beprovided for all bends on exposed steel pipes to resist the full thrustregardless of the diameter of the pipe.
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Page 5 and 6: SectionPage No.3.12 Cathodic Protec
Page 7 and 8: List of Appendices4.4 Schematic Arr
Page 9 and 10: - 2 -EquivalentEquivalentNominalNom
Page 11 and 12: - 4 practicable and aesthetically
Page 13 and 14: - 6 with a built-in by-pass. In s
Page 15 and 16: - 8 leaks and bursts in the distr
Page 17 and 18: - 10 1.3.13 Contact Points for Le
Page 19 and 20: - 12 joints and collars, Appendix
Page 21 and 22: - 14 -than 127 m headFor connecting
Page 23 and 24: - 16 http://www.emsd.gov.hk/emsd/
Page 25 and 26: - 18 -Where the works is carried ou
Page 27: - 20 3.5 Laying PipesA number of
Page 31 and 32: - 24 Backfilling involves two ope
Page 33 and 34: - 26 and chemical analyses. The p
Page 35 and 36: - 28 3.14 Fire HydrantsThe locati
Page 37 and 38: - 30 SECTION 4 - REPAIR, REHABILI
Page 39 and 40: - 32 of the proposed water main,
Page 41 and 42: - 34 (iii)“Sliplining” is def
Page 43 and 44: - 36 The advantages and disadvant
Page 45 and 46: - 38 again as necessary to confir
Page 47 and 48: - 40 Step 7: Post-lining CCTV Sur
Page 49 and 50: - 42 Step 6: Hydrostatic Pressure
Page 51 and 52: - 44 pipe is ductile or brittle)
Page 53 and 54: - 46 [Remark: The exposed lining
Page 55 and 56: - 48 existing lining so that stra
Page 57 and 58: Appendix 1.1Sheet 2 of 6normal circ
Page 59 and 60: Appendix 1.1Sheet 4 of 6b) If the m
Page 61: Appendix 1.1Sheet 6 of 6Figure 4 (a
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Appendix 3.3Sheet 1 of 7Guidelines
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Appendix 3.3Sheet 3 of 7ItemItem De
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Appendix 3.3Sheet 5 of 7FromTo: [Pr
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Appendix 3.3Sheet 7 of 7(E) Suspici
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Appendix 4.2Sheet 1 of 2Advantages
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