CHAPTER 1000. Excavation for Pipelines.
1001. General. This section covers the requirements for trenching for underground pipelines.
1002. Excavation for Pipelines. Excavation for pipelines shall follow lines parallel to and equidistant from the location of the pipe centerline. Trenches shall be excavated to the depths and widths required to accommodate the construction of the pipelines as follows:
1003. TRENCH WIDTH. Trench width at the ground surface may vary depending on depth, type of soil, and position of surface structures. The minimum clear width of the trench, sheeted or unsheeted, measured at the springline of the pipe should be 1 ft. (300 mm) greater than the outside diameter of the pipe. The maximum recommended clear width of the trench at the top of the pipe is equal to the pipe outside diameter plus 2 ft. (600 mm). If the maximum recommended trench width must be exceeded or if the pipe is installed in a compacted embankment, then pipe embedment should be compacted to a point of at least 2 1/2 pipe diameters from the pipe on both sides of the pipe or to the trench wall, whichever is less.
(1) Excavation shall not be carried below the grade shown on the approved drawings. Any unauthorized excavation made below grade for any reason shall be backfilled in accordance with these specifications.
(2) Excavation for trenches in ledge rock, cobblerock, stones, mud or other material unsatisfactory for pipe foundation, shall extend to a depth of at least four inches below the bottom of the pipe. A bedding of special material shall be placed and thoroughly compacted with pneumatic tampers in four inch lifts to provide a smooth, stable foundation. Special foundation material shall consist of suitable materials free from roots, sod or vegetable matter. Trench bottoms shall be hand shaped as specified in paragraph 1 above.
(3) Where unstable earth or muck is encountered in the excavation at the grade of the pipe, a minimum of six inches below grade will be removed and backfilled with crushed gravel to provide a stable subgrade.
(4) The maximum width of trench, measured at the top of the pipe, shall be as narrow as possible, but not wider than 12 inches on each side of sewer pipe and 15 inches on each side of water pipe.
1004. Stockpiling excavated material. All excavated material should be stockpiled in a manner that will not endanger the work or obstruct sidewalks and driveways. Hydrants under pressure, valve‑pit covers, valve boxes, curb‑stop boxes, fire and police call boxes, and other utility controls should be kept accessible.
1005. Control of Ground Water. All trenches shall be kept free from water during excavation, fine grading, pipe laying, jointing, and embedment operations. Where the trench bottom is mucky or otherwise unstable because of the presence of ground water, and in cases where the static ground water elevation is above the bottom of any trench or bell hole excavation, such ground water shall be lowered to the extent necessary to keep the trench free from water and the trench bottom stable when the work within the trench is in progress. Surface water shall be prevented from entering trenches.
1006. Gravel Foundation for Pipe.
(1) Wherever the subgrade material does not afford a sufficiently solid foundation to support the pipe and superimposed load and where water must be drained to maintain a dry bottom for pipe installation and at other locations as previously defined, the subgrade shall be excavated to the specified depth and replaced with crushed rock or gravel. See A.S.T.M. D‑2321
(2) The gravel material shall be deposited over the entire trench width in six inch maximum layers, each layer shall be compacted by tamping, rolling, vibrating, spading, slicing, rodding or by a combination of one or more of these methods. In addition, the material shall be graded to produce a uniform and continuous support for the installed pipe.
1007. Blasting. Blasting will not be allowed except by permission from the Engineer. The Contractor shall comply with all laws, ordinances, and applicable safety code requirements and regulations relative to the handling, storage, and use of explosives and protection of life and property, and he shall be fully responsible for all damage attributable to his blasting operations. Excessive blasting or overshooting will not be permitted and any material outside the authorized cross section which may be shattered or loosened by blasting shall be removed by the contractor.
1008. Sheeting, Bracing and Shoring of Excavation.
(1) Excavation shall be sheeted, braced, and shored as required to support the walls of the excavations to eliminate sliding and settling and as may be required to protect the workmen, the work in progress and existing utilities and improvements. All such sheeting, bracing and shoring shall comply with the requirements of the Utah State Industrial Committee.
(2) Prior to any individual, workman, or inspector proceeding into any open excavation which requires bracing, sheeting, shoring, or otherwise personnel protection devices: approval for such proceeding must be granted in person by the City Engineer after careful examination of existing conditions and inspection of all trench shoring materials. Workers shall not proceed until such approval is granted.
(3) All damage resulting from lack of adequate sheeting, bracing and shoring shall be the responsibility of the contractor and the contractor shall affect all necessary repairs or re‑ construction resulting from such damage.