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is buried, the horizontal loading char- <br />acieristics of the soil should be evalu- <br />ated. If the site is on a side -hill, a <br />geologic investigation should be made <br />to evaluate the safety of the site against <br />sliding. All reservoir sites should be <br />examined by a geologist for faults. <br />Obviously, the presence of any faults <br />suspected to be active would dictate <br />selection of another site. <br />If the site of a structure is on hard <br />rock, and the rock, after blasting or <br />rooting, comes out in large chunks, <br />area and work across the entire site <br />with a high pressure hose, making a <br />slurry of the sand so it will wash into <br />all crevices and depressions. Addi- <br />tional sand may be necessary to bring <br />the site to the required grade. Com- <br />paction of the sand subgrade can be <br />completed with a vibratory roller. <br />2. Need for underdrains. Under - <br />drains prevent uplift caused by high <br />ground water or by leakage from the <br />reservoir structure. If the reservoir <br />subgrade is relatively impervious, the <br />d it 9 in.\ Slope 1 per cent /2-8 of Earth "Water Surface <br />D <br />r <br />--- <br />_- <br />18 It 7' in. <br />T <br />WatenYop <br />19ft <br />'=- <br />19 a'— <br />m <br />�o <br />191t <br />6 m <br />24 in. Diam. <br />m <br />� <br />. o <br />9 <br />y <br />r <br />Plan Dimensions <br />'< <br />Irregular, Maximum <br />Dimension 560 It <br />:o � Waterstop <br />N <br />Waterstop <br />e <br />a <br />N <br />2 It 10 in. Underdrain <br />slope 1 per cent <br />Far. <br />,u� <br />Fig. 6. Dunsmuir 8eservoir, Oakland, Calif. <br />The capacity of this reservoir is 64.4 mil gal in two basins. <br />leaving an uneven surface, the problem <br />arises how to treat the surface to in- <br />sure uniform support of the structure. <br />One way, of course, is to remove com- <br />pletely all loose material and then back - <br />fill with concrete, as is customary for <br />a dam foundation. Although such <br />treatment is effective, it is expensive <br />and usually not necessary. An inex- <br />pensive method that the author has <br />found effective is to place 4-6 in. of <br />washed concrete sand over the entire <br />C <br />leakage will not drain away readily, <br />and when the reservoir water level is <br />lowered, the hydrostatic pressure from <br />water acting on the outside surfaces of <br />the structure may be high enough to <br />cause failure of the floor through up- <br />lift. Underdrains are especially impor- <br />tant where reservoir sides are built <br />on a slope. <br />Underdrains also insure the stability <br />of cantilever retaining walls used in <br />reservoirs and other hydraulic struc- <br />RICHARD BRADY &ASSOCIATES, INC. F-56 <br />25B-134 <br />