(A) Pipe embedment shall mean that portion of the material placed within the trench from the sewer subgrade to a point at least six inches, but no more than 12 inches, above the outside top of the pipe. SEWER SUBGRADE is defined in § 33.191
(B) (1) Pipe embedment material. Import:
(a) Shall be three-fourths inch by one-half inch clean, crushed rock. Alternate backfill bedding material may be used only if prior written approval is granted by the District Engineer. This approval is on a case-by-case basis; and
(b) Pipe bedding material shall be compacted by and tamping to a minimum 90% relative compaction from six inches below the bottom of pipe to a point 12 inches above top of pipe.
(2) Backfill.
(a) 1. Import backfill materials is an approved combination of gravel, sand or rock material, free from deleterious substances, graded so that it will compact readily to a stable base with the following minimum requirements meeting the Caltrans Class 2 aggregate base standard for three-fourths inch maximum grading. The material shall be of such size that the percentage composition by weight, as determined by laboratory sieves, will conform to the following grading:
Sieve Size | Percent Passing (by weight) |
1-inch sieve | 100% |
3/4-inch sieve | 90 - 100% |
No. 4 sieve | 35 - 60% |
No. 30 sieve | 10 - 30% |
No. 200 sieve | 2 - 9% |
2. The material shall also have a minimum sand equivalent (Test Method of Northern California 217) of 25, a minimum resistance (R) value (Test Method of Northern California 301) of 78 and a minimum durability index (Test Method of Northern California 229) of 35.
(b) Native backfill may be used for sewer lines located in areas outside of paved roads. Material free from vegetal matter, refuse, stones or clods larger than four inches in diameter and containing sufficient fines so that all voids will be filled when compacted, and so constituted that compaction requirements can be met.
(3) Trench excavation material. Acceptable trench excavation material shall be that material which is free from vegetal matter and refuse; shall contain no concrete, stones or clods larger than three-fourths-inch in diameter; and shall contain sufficient fines so that all voids will be filled when compacted.
(4) Pipe embedment installation.
(a) Main and laterals in public utility and District easements, public rights-of-way and paved private property shall use or embed pipes with import backfill material.
(b) Trenches for private laterals (building sewers) in unpaved private property from property line to building shall be backfilled with approved import backfill material to 12 inches above the top of pipe and the balance with import backfill or approved native backfill material.
(Ord. 2019-02, passed 4-25-2019)