Trenching for all pipes shall be in open cut to the lines and grades shown on the plans, except that sections not to exceed eight feet in length may be in a tunnel where necessary in the opinion of the county engineer, to protect existing trees or structures. Where tunnels are required, the roof shall be sloped forty-five degrees downward from each end. Any paving which is to be removed shall be scored at or adjacent to the edges of the trench to such a depth and in such a manner before trenching operations are begun as to avoid damage to paving outside the trench area during trenching operations. (Ord. 383 § 310, 1974).

The sides of all excavations shall be supported in the manner set forth in the “Construction Safety Orders” issued by the Division of Industrial Safety, Department of Industrial Relations, state of California. Sheet piling and other timbering shall be withdrawn in such a manner as to prevent caving of the walls of excavations or damage to piping or other structures. Whenever timber or other sheeting is driven to a depth below the elevation of the top of the pipe, that portion of the sheeting below the elevation of the top of the pipe shall not be disturbed or removed. (Ord. 383 § 311, 1974).

The contractor shall remove all water which may accumulate in the excavation during the progress of the work so that all work can be in the dry. Trenches shall be kept free from water while the pipe or other structures are installed, while concrete is setting and until backfill has progressed to a sufficient height to anchor the work against possible flotation. (Ord. 383 § 312, 1974).

Bedding for all piping installations shall be sufficient for the loads to which the pipe may be subjected as determined by the county engineer, but no less than the minimum herein set forth.

If soil conditions are stable, and the trench bottom is of a material that can be cut true and straight, pipe can be installed using the uniform trench bottom for support. Bell holes must be dug to provide a minimum clearance of two inches below the couplings.

The trench bottom must be straight, free of bumps or hollows and at the correct grade. As the pipe is laid, any irregularities in the trench bottom must be leveled off or filled in with tamped soil.

Where the trench bottom is in hardpan, rock or any similar unyielding bed, the trench should be excavated at least six inches below trench grade and then brought back to grade with selected, tamped soil before laying the pipe.

In unstable or soft soils, the trench shall be excavated to stable soil and refill with selected material such as gravel or crushed rock until pipe grade is reached.

When spreading refill soil on the trench bottom, provide a minimum clearance of two inches below the coupling.

The initial backfilling shall be hand-placed to at least twelve inches over the pipe with a suitable material free of large stones greater than one-half inch diameter and in cold weather, free of frozen lumps. Backfill material shall be placed in such a manner as to not injure or disturb the pipe and then thoroughly tamped at layers of four inches.

The balance of the backfill, which is from twelve inches over the top of the pipe to finished grade shall have relative compaction equal to adjacent undisturbed soil, but in no case less than ninety percent. Backfill material shall be free from too large stones, organic matter or other deleterious substances. (Ord. 383 § 313, 1974).