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<br />,. ." <br /> <br />'i <br /> <br />I:NS'l'ALLA'l'J:ON <br /> <br />Minimum "Depth of Cover. The minimum depth of cover over the <br />pipeline shall be as follows: <br /> <br />PIPE DIAMETER (IN.) <br /> <br />MINIMtJM DEPTH OF COVER (IN.) <br /> <br />1/2 <br />3 <br /> <br />2 1/2 <br /> <br />18 <br /> <br />5 <br /> <br />24 <br /> <br />6 <br /> <br />27 . <br /> <br />30 <br /> <br />Trench Construction. For 4 in. through 18 in. diameter pipe <br />sizes, the minimum trench width shall be 1.8 inches greater <br />than the pipe.diameter for vertical walled trenches and 12 <br />inches greater than the pipe diameter for trenches with sloped <br />sidewalls, (see Figure 1.). The minimum trench width for pipe <br />sizes larg.er than 18 inches shall be 36 inches greater than <br />the pipe diameter for vertical walled trenches and 18 inches <br />greater than the pipe diameter for trenches with sloped <br />sidewalls, (see Figure 2). This minimum trench width criteria <br />will not apply if precision excavation methods are used. <br /> <br />,_.' -- <br /> <br />Thrust Blocks. Concrete used for thrust blocks shall be <br />allowed to cure for three days, minimum, prior to backfilling <br />or pressurizing the pipe. <br /> <br />Initial Backfill. All initial backfill shall have a maximum <br />particle size of one (1) inch~. The finished initial backfill <br />for 1.8 It diameter and smaller pipes shall extend to the top of <br />the pipe, (see figure 1). Initial backfill for 20 inch <br />diameter and larger pipes shall be coarse-sand or gravel, and <br />shall extend from the pipe bedding to a minimum depth equal to <br />70 percent of the pipe diameter, (see figure 2). <br /> <br />Compaction shall be accomplished by either water packing or by <br />hand or hand directed mechanical means. <br /> <br />'---Wateru.Packing-shall- be- -accompl-ished--as. -described-in u--NHCP-4 3-0- <br />DO, ex~ept the initial a~d final backfill "shall be of <br />sufficient depth to cover the top of the pipe after <br />consolidation. . The pipe shall be filled gradually, (less than <br />1. ~eet per second), prior to water packing, and enough water <br />shall be added to the pipe trench to saturate the initial <br />backfill. . <br /> <br />USDA-SCS Colorado <br /> <br />CQ-430-DD-3 <br /> <br />. March 1992 <br />