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<br />1. For manhole diameter to sewer diameter ratios between two (2) <br />and six (.6), the variation in head loss was insignificant. <br /> <br />2. The most signific':l.nt reduction in head l,Jssoccurs when the <br />manhole is shaped by benching the bottom of the manhole up to <br />the top of 'the pipe. This appears tel provide a better <br />channelization of the flow, which reduces the losses. <br /> <br />3. Some testing was also performed for open channel flow <br />condi tions. These tests generally showed t:hat the energy <br />losses were less than for pressure fle.w. Since most storm <br />sewers are not pressurized, the use of the coefficients should <br />be conservative. <br /> <br />This information is pJ::esented to aid the c1es;ignElr in selecting <br />suitable energy loss coefficients for situcltions not covered by <br />these criteria. <br /> <br />6.4 Vertical A1iqDlllen1t <br /> <br />The sewer grade shall be such that a minimum cover i.s maintained to <br />withstand AASHTO HS-20 (or as designated by the Public Works <br />Department) loading on the pipe. The minimum cover depends upon <br />the pipe size, type and class, and soil bl!dcling condition, but <br />shall not be less than 12 inches on any point along the pipe. <br /> <br />The minimum clearance between storm sewer and water main, either <br />above or below, shall be 1 foot. Concrete encaseme,nt of the water <br />line will be required for clearances of less than or equal to 1 <br />foot. <br /> <br />The minimum clearance between storm sewer and :;anitary sewer, <br />either above or below, shall also be 1 foot. In a.ddition, when a <br />sanitary sewer main li,,!s above a storm sewer, or w'ithin 18 inches <br />below, the sanitary sewer shall have an impervious l!ncasement or be <br />constructed of structural sewer pipe for a minimum of 10 feet on <br />each side of where the storm sewer crosses. <br /> <br />6.5 Horizontal AliqDIII1IJnt <br /> <br />storm sewer alignment between manholes shall be straight for storm <br />sewers less than 48-i.nches in diameter. s'torm sewers may be <br />constructed with curvi.linear alignment for 48-inch diameter and <br />larger pipe by either the pulled joint method! e,r by radius pipe in <br />accordance with Table 6-1. The limitations on the radius for <br />pulled joint pipe is dependent on the pipe le:ng1r.h and diameter, and <br />amount of opening permitted in the joint. The ma.ximum allowable <br />joint pull shall be ~ of an inch. The minimum parameters for <br />radius type pipe are shown in Table 6-1. The radius requirements <br />for pipe bends is dependent upon the manufact'~r'ar's specifications. <br /> <br />6-6 <br /> <br />I ' <br />I <br />I <br />I <br />I <br />I <br />I <br />I I <br />II <br />I <br />I <br />I ' <br />I <br />I' <br />I <br />I <br />I <br />I <br />I <br />