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<br />e <br /> <br />e <br /> <br />e <br /> <br />DRAINAGE CRITERIA MANUAL (y. 2) <br /> <br />HYDRAULIC STRUCTURES <br /> <br />loadings that can occur for a variety of conditions such as during construction or during dominant low <br />flows and flood flows. The soilslfoundation engineer combines this information with the on-site soils <br />information to determine foundation requirements. Both engineers should work with a structural engineer <br />to establish final loading diagrams and in selection and sizing of structural components. <br /> <br />TABLE HS-ll <br />General Cutoff Technique Suitability <br /> <br /> Drop Height (It) <br />Soil Conditions 2 4 8 12 <br />Sands and gravel over bedrock with sufficient depth of SP' SP' SplSwB 1 SplSwB 1 <br />material to provide support-groundwater preyalent CTc CT clST ST ST <br /> CTf CTf/CTI <br />Sands and gravel with shallow depth to bedrock- CTc CTclST ST ST <br />groundwater prevalent CW CW CW SW <br /> SP' SP' SP' SwB' <br />Sands and gravel with large depths to bedrock- SP SP SP SPISwB <br />groundwater prevalent CTc CT c1ST ST ST <br />Sands and gravel, no groundwater, or water table SP SP SP SPISwB <br />normally below requirement (for variation caused by CTf/CTI CTI CTI CTI <br />depth to bedrock, see first case) CW CW <br />Clay (and silts}-medium to hard CTc CT CT CT <br /> CW Reduce length for difficult backfill <br /> conditions <br /> CTI/CTf Only for local seepage zoneslsilts <br /> ST Expensive-for special problems <br />Clays (and silts}-soft to medium with lenses of CP SP SP SP/SwB <br />permeable material--groundwater present CTc CTc CTclST ST <br />Clay (and silts}-soft to medium with lenses of SP SP SP SPISwB <br />permeable material (may be moist but not significant CTc CTc CTclST ST <br />groundwater source) CTf CTI CTI CTI <br /> CW CW CW CW <br /> <br />1 Consider scour in sheet pile support. <br />, Excavate into bedrock and set into concrete. <br /> <br />Leqend: <br /> <br />SP <br />SwB <br />CTc <br />ST <br /> <br />Sheet pile <br />Sheet pile with bracing and extra measures <br />Cutoff trench backfilled with concrete <br />Slurry trench; similar to CTc, but trench walls are supported with slurry and then later replaced <br />with concrete or additives that provide cutoff <br />Cutoff wall; conventional wall, possibly with footer, backfilled; note that the effective seepage <br />length should generally be decreased because of backfill <br />Cutoff trench with synthetic liner and fill <br />Cutoff trench with clay fill <br /> <br />CW <br /> <br />CTI <br />CTf <br /> <br />06/2001 <br />Urban Drainage & Flood Control DistricI <br /> <br />HS-35 <br />