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2 .2 .4 . Brine Main <br /> Excavation and Preparation of Trench (Cont'd) <br /> work or adjacent structures orproperty, <br /> The Contractor may, where it will not interfere with � <br /> slope the sides of excavation from a point starting one ( 1 ) foot above the top of the pipe. <br /> Maximum trench widths at the surface for gravity sewer shall be as follows . <br /> In areas where existing utilities, existing structures, limited working area or the necessity to <br /> maintain traffic flow require that the trench width be confined to a minimum area, the Engineer <br /> ' will determine the allowable trench width and will instruct the Contractor accordingly. <br /> Any part of the trench excavated below grade shall be corrected with thoroughly compacted <br /> material approved by the Engineer. <br /> When an unstable subgrade condition is encountered and, in the opinion of the Engineer, it <br /> cannot support the pipe, an additional depth shall be excavated and refilled to pipe foundation <br /> grade with select backfill or other suitable material as required by the Engineer to achieve a <br /> satisfactory trench bottom. <br /> ' Ledge rock, boulders and large stones shall be removed to provide clearance to each side of, and <br /> below, all pipe and accessories. This clearance for pipe and accessories shall be six (6 ") inches. <br /> Excavations below subgrade when rock and boulders are encountered, shall be refilled to <br /> subgrade with select backfill material approved by the Engineer and thoroughly compacted. <br /> Whenever necessary to prevent caving, trench excavations in soils such as sand, gravel and sandy <br /> soil, shall be adequately sheeted and braced. Where sheeting and bracing are used, the trench <br /> width shall not be less than that herein before specified. <br /> ' As backfill is placed, if sheeting is to be withdrawn, it shall be withdrawn in increments not <br /> exceeding one ( 1 ) foot and the void left by the withdrawn sheeting shall be filled and compacted. <br /> All excavated material shall be piled in a manner that will not endanger the work and will avoid <br /> obstructing sidewalks and driveways. Gutters shall be kept clear or other satisfactory provisions <br /> made for street drainage. <br /> ' The use of trench-digging machinery will be permitted except where its operations will cause <br /> damage to trees, buildings or existing structures above or below the ground. At such locations, <br /> hand methods shall be employed to avoid such damage. <br /> 12 <br />