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4 .6? <br />Our Job 81-20-00 age <br />Subdrains, which serve to collect and di-scharge <br />water, are placed where water is encountered at the time <br />of construction or where the occurrence of seepage is <br />anticipated. Subdrains are provided to prevent saturation <br />and/or consequent h,vdrostatic pressure buildup. <br />Detailed recommendations for subdrains are given <br />in the geotechnical report or in memoranda issued on a <br />part icul ar proj ect. <br />CanYon Subdra ins .Can)'on bot ton subdrains are <br />to be installed in a rrvrr ditch or trench cut into the firn <br />earth material in the lowest portion of the cut nade to <br />remove unsuitable material. Subdrains sha1l con-sist of <br />perforated, asbestos cement, plastic or asphalt-coated netal <br />pipes, with a crushing strength of at least 1000 pounds <br />(or equivalent), embedded in filter material specified by <br />the Consultant. The subdrain rnust be placed with a minirnum <br />gradient, as specified, tor"'ard the outlet. <br />The detailed design of the subdrain will depend <br />on loca1 conditions, and any departure from the standards <br />discussed in this Section will be sPecified in the geo- <br />technical report. Plates B-4.1 and B'4.2 - Typical Canyon <br />Subdrain illustrate two tyPes of typical canyon subdrain. <br />4.63 Subdra ins Behind Si dehi 1 1 an d Buttress Fi11 Masses- <br />Subdrains <br />sidehill <br />water is <br />as specified above are also to be installed behind <br />and other structurally critical fill masses wherever <br />expected. Plate B-4.3 - Typical subdrain, sidehill