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<br />HYDRAULIC STRUCTURES <br /> <br />DRAINAGE CRITERIA MANUAL (V. 2) <br /> <br />4. In the case where two vertical cutoffs are used, then Equation HS-13 should be used along with <br />Equation HS-14 to check the short path between the bottom of the vertical cutoffs. <br /> <br />e <br /> <br />c = (Lv-us + <br />W2 <br /> <br />2LH_C + LV-DS) <br />Hs <br /> <br />(HS-14) <br /> <br />in which: <br /> <br />CW2 = creep ratio where two vertical cutoffs are used <br /> <br />Lv.us = vertical distance on the upstream side of the upstream cutoff (ft) <br /> <br />Lv_Ds = vertical distance on the downstream side of the downstream cutoff (ft) <br /> <br />LH_c = horizontal distance between the two vertical cutoffs (ft) <br /> <br />5. If there are seepage lengths upstream or downstream of the cutoffs, they should be treated in the <br />numerator of Equation HS-14 similar to Equation HS-13. Seepage is controlled by increasing the <br />total seepage length such that Cw or CW2 is raised to the value listed in Table HS-7. Soils tests <br />must be conducted during design and confirmed during construction. <br /> <br />6. The upward pressure to be used in design may be estimated by assuming that the drop in <br />pressure from headwater to tailwater along the contact line of the dam and foundation is <br />proportional to the weighted-creep distance. <br /> <br />e <br /> <br />TABLE HS-7 <br />Lane's Weighted Creep: Recommended Ratios <br /> <br />Material Ratio <br />Very fine sand or silt 8.5 <br />Fine sa nd 7.0 <br />Medium sand 6.0 <br />Coarse sand 5.0 <br />Fine oravel 4.0 <br />Medium gravel 3.0 <br />Coarse oravel includino cobbles 3.0 <br />Boulders with some cobbles and oravel 3.0 <br />Soft clay 3.0 <br />Medium clav 2.0 <br />Hard clay 1.8 <br />Very hard clay or hardoan 1.6 <br /> <br />2.6.2 Foundation/SeeDaae Control SYstems. Table HS-8 presents some typical foundation conditions <br />and systems that are often used for various drop heights. For each condition, cutoff types are listed in <br />general order of preference for guidance purposes only. The hydrauiic engineer must calculate hydraulic <br /> <br />e <br /> <br />HS-34 <br /> <br />06/2001 <br />Urban Drainage & Flood Control District <br />