A. General. Unless otherwise recommended in the approved soil engineering
report fills shall conform to the provisions of this Section.
In the absence of an approved soil engineering report these provisions may be
waived for minor fills not intended to support structures. Such fills shall be
subject to review at the discretion of the Director.
B. Ground preparation. The ground surface shall be prepared to receive
fill by removing vegetation, noncomplying fill, top-soil, and other unsuitable
materials scarifying to provide a bond with the new fill, and where slopes are
steeper than 5 to 1, and the height greater than 5 feet, by benching into
competent material or sound bedrock as determined by the soils engineer. The
bench under the toe of a fill on a slope steeper than 5 to 1 shall be at least
10 feet wide. The area beyond the toe of fill shall be sloped for sheet overflow
or a paved drain shall be provided. Where fill is to be placed over a cut the
bench under the toe of a fill shall be at least 10 feet wide but the cut must be
made before placing fill and approved by the soils engineer and engineering
geologist as a suitable foundation for fill. Unsuitable soil is soil which in
the opinion of the Director or the civil engineer or the soils engineer or the
engineering geologist, is not competent to support either soil or fill, to
support structures or to satisfactorily perform the other functions for which
the soil is intended.
C. Fill material. Only permitted material free from tree stumps,
detrimental amounts of organic matter, trash, garbage, sod, peat, and similar
materials shall be used. Rocks larger than 6 inches in greatest dimension shall
not be used unless the method of placement is properly devised, continuously
inspected, and approved by the Director.
The following shall also apply:
Rock sizes greater than 6 inches in maximum dimension shall be 10
feet or more below grade, measured vertically.
2. Rocks shall be placed so as to assure filling all voids with
fines. Topsoil may be used in the top 12-inch surface layer to aid in planting
D. Compaction of fill. All fills shall be compacted to a minimum
relative dry density of 90 percent as determined in accordance with ASTM
Standard D-1557-78. Field density verification shall be determined in accordance
with ASTM Standard D-1556-82 or equivalent and must be submitted for any fill 12
inches or more in depth where such fill may support the foundation for a
structure. A higher relative dry density, or additional compaction tests, or
both, may be required at any time by the Director.
E. Fill slope. The slope of fill surfaces shall be no steeper than is
safe for the intended use. Fill slopes shall be no steeper than 2 horizontal to
F. Drainage and terracing. Drainage and terracing shall be provided
and the area above fill slopes and the surfaces of terraces shall be graded and
paved as required by Section 24.70.100.