(a) The ground shall be excavated in open trenches of sufficient width and depth to provide sufficient room within the limits of excavation, or lines of sheeting and bracing, for the proper construction of the sewer and its appurtenances, as shown on the approved drawings. The excavation of the trench shall not advance more than 200 feet ahead of the completed masonry and pipe work except where, in the opinion of the Village, it is necessary to drain wet ground. Where trench excavation is carried ahead of the contemplated masonry and pipe work, the elevation of the bottom of the trench shall be continually checked, to the satisfaction of the Engineer. In clay or dirt excavation, the bottom of the excavation shall be at least D/4 and a minimum of four inches below the sewer invert. This space shall be backfilled and compacted to pipe grade with granular material, well graded with a minimum of voids. The minimum size of such granular material shall be retained on a No. 8 sieve and the maximum size shall pass a three-quarter inch sieve. After placing the pipe, additional granular material shall be placed in the trench and compacted halfway up the pipe barrel. The remainder of the sides and a depth of twelve inches over the top of the pipe shall be filled with carefully compacted material. Excavation made below that herein required shall be backfilled only with the aforementioned granular material, well compacted.
(b) Bell holes of sufficient depth to insure an even bearing on the main body of the pipe and to provide sufficient room for the making of the joint shall be formed in the bottom of the trench whenever bell and spigot pipe are being laid.
(c) Rock excavation, as defined in these specifications, if encountered, shall be removed to not less than six inches below the bottom of the sewer or masonry work. Irregularities of the rock and the cut, below grade, shall be refilled only with sand or fine gravel well rammed into place and firmly compacted.
(d) Where pipe sewers are built, the width of the trench at the top of the pipes shall not exceed four-thirds the internal diameter of the sewer plus eight inches, provided that a greater width may be permitted by the Engineer when it is necessary to sheet the trench. There shall be at least four inches clear space on each side of the pipe to permit tamping when sheeting is used. Tunnels for pipe sewers beneath existing structures, pavements, sidewalks and railroad tracks, where shown on the approved drawings or where allowed per written authorization of the Engineer, shall be installed in compliance with the specifications for short tunnels.
(e) Sheeting and bracing shall be placed in the ditch as may be necessary for the safety of the work and the public, for the protection of the workmen, adjacent properties and for the proper installation of the work. Sheeting and/or bracing shall be progressively removed as the backfill is placed in such a manner as to prevent the caving-in of the sides of the trench or excavation and to prevent damage to the work. Sheeting which is placed for the protection of the public, adjacent properties or structures shall not be removed until the backfill has been placed and thoroughly tamped. While being drawn, all vacancies left by this sheeting shall be carefully filled with sand free from silt, rammed into place, puddled or otherwise firmly compacted. Sheeting and/or bracing shall be left in place if so ordered by the Engineer.
(f) Where designated on the approved drawings or when ordered by the Engineer, crushed rock or gravel refill, concrete cradle or encasement, timber cradle, piling or a combination thereof shall be furnished and installed. After the trench has been opened and to grade, it shall be examined by the Engineer who shall determine whether or not it is satisfactory for pipe laying or if it is necessary to stabilize the base, install concrete cradles or drive piling. Any pipe laid in a trench that has not been examined and approved by the Engineer is done so at the contractor’s own risk. Where deemed necessary by the Engineer, a soil test shall be made as hereinafter specified. Crushed rock or gravel used to stabilize a trench bottom or to provide an under-drain shall have a minimum size of one inch and a maximum of two and one-half inches well graded between the above limits. The minimum thickness of the layer installed shall be six inches, and the balance of the material must have sufficient amounts of graded crushed stone or coarse sand to fill all voids between rock fragments.
(g) When sewer invert or cradle is to be placed on any material which will run or move when wet, sheeting must be employed during construction to keep adequate side supports on each side of the sewer trench so that the weight of the cradle and/or sewer will not tend to cause the bottom material to run to each side of the excavation. In extremely fluid materials, at the direction of the Engineer, wood sheeting shall be used and left in place. In this case, the concrete cradle shall extend the entire width between the sheeting. Concrete for concrete cradle shall be volume proportioned not less than one part Portland cement, three parts of fine aggregate and five parts of coarse aggregate, with only enough water added to make a workable mix.
(Ord. 352. Passed 10-22-62.)