PDF PDF.

- 19 ­may be designated as industrial area or are likely to be used for industrialpurposes.Any proposal to lay a main on filling exceeding 1.5 m in depth must becarefully considered with regard to the degree of consolidation and the risk ofsubsequent movement. Moreover, filling over a main in excess of 2.1 mabove the crown of the pipe, except where deeper laying for short lengths isnecessary to avoid obstructions, should not be accepted without carefulconsideration. In either case, the proposal should be referred to the ChiefEngineer/Region for approval.The above general guidelines do not preclude analysis to be carried out inspecial cases. Special design considerations should be made for pipesexceeding 1200 mm diameter.If it is necessary to lay a main with cover less than the specified minimumvalue, consideration must be given to the amount of cover needed for valves,and to the necessity for special protective measures. Only with the approvalof the Chief Engineer/Region should water mains with shallow cover withadequate protection be laid to suit the site conditions. In order to minimisethe number of water mains damaged by road opening contractors, properrecords on these shallow covered water mains (i.e. those mains with coversless than 450 mm under footway and 900 mm under carriageway as stipulatedin the Conditions of Excavation Permit promulgated by HyD) in the DigitalMapping System should be made for future reference.To facilitate the keeping of a central register of all shallow covered watermains, all new shallow covered water mains laid, existing unrecorded shallowcovered water mains discovered, or existing recorded shallow covered watermains altered should be reported to the Drawing Office as detailed in Section3.14. In fact, reporting of anomalies about shallow covered mains is part ofthe practice of reporting differences between details shown in the DigitalMapping System and those found on site to the Drawing Office forrectification.Special cover requirements are stipulated in HyD’s Technical Circular No.3/90, especially for water mains running along kerb zones. Waiver forshallow covered mains should be obtained from HyD before seeking theapproval of the relevant Chief Engineer/Region of WSD, if mains not meetingcover requirements have to be laid in carriageway, footpaths and cycle trackswhich are under the jurisdiction of HyD.Procedures regarding the laying of small diameter mains in footpaths and backlanes are covered by DI No. 929 “Laying of Connections and InsideService/Fire Service on Government Land”.