§ 15.01.420. Backfilling.

The contractor shall not proceed to backfill until each section of utility line has been inspected by the city. Backfill shall be carefully placed around and over pipes and shall not be permitted to fall directly on a pipe from such a height as to cause damage. In these specifications, the process of preparing the trench bottom to receive the pipe to a level at the pipe center line (spring line) is defined as bedding except for plastic, corrugated metal in which case the bedding is considered to extend to twelve inches above the top of the pipe. Where the excavated material has rocks over two inches in diameter or soils do not meet ASTM requirements, the zone shall be backfilled with modified bedding materials meeting the following gradations: one hundred percent passing, a one-inch screen and five percent passing a No. 4 sieve.

The bedding material shall first be placed so that the pipe is supported for the full length of the barrel with full bearing on the bottom segment of the pipe equal to a minimum of one-half of the diameter of the barrel, then the remainder of the bedding shall be placed. Alternative outside methods of pipe laying which are recommended by the pipe manufacturer may be used if approved by the city engineer.

Trench backfilling above the level of the pipe bedding shall normally be accomplished with native excavated materials and shall be free from frozen earth, organic material, rocks and solid objects larger than eight inches in diameter, except as required to protect pipe as per manufacturers specifications.

The backfill in all utility trenches shall be ether compacted or consolidated according to the requirements of the materials being placed. The in-place density shall be a minimum of ninety-five percent of the maximum dry density as determined by ASTM D 1557 (modified Proctor compaction test) for all granular materials. The city engineer may approve the use of AASHTO T-99 (standard Proctor compaction test) only when materials being compacted warrant consideration of such measurement methods as recommended by the Utah Chapter of the American Public Works Association or other recognized city standard reference publication for a given material type or other reasons as deemed appropriate for use of the AASHTO T-99 method. The ASTM D 1557 method shall be considered the default standard for all compaction efforts. Perform a minimum of one test per two hundred linear feet of trench per eight-inch material lift depth of trench backfill to assure overall compliance. Each utility lateral trench shall be considered a separate trench for purposes of minimum testing requirements. In the event that testing indicates additional compaction is required, perform additional compaction efforts with commensurate additional testing as needed to assure compliance. The city engineer shall approval all trench backfill prior to proceeding to any pavement system placement on a utility trench.

(Ord. No. 2007-07-31, § 4.8, 7-10-2007; Ord. No. 2012-05-15, § 1, 5-8-2012)