Sec. 7-3.22. Buttress fills.
   (a)   General. A buttress fill is a designed compacted earth fill used for providing lateral support to an unstabilized earth or rock mass. All buttress fills shall be designed in accordance with the recommendations and design criteria, including the subdrain system, submitted by the soils engineer or engineering geologist with the approval of the City Engineer.
   (b)   Foundation. The ability of the foundation soil to support the buttress shall be investigated, and additional benching shall be required to what is otherwise specified for ordinary fills. The soils engineer shall provide specifications for keying the base of the buttress and for bonding the buttress to the natural ground.
   (c)   Subdrains. Subdrains which blanket the entire back face of the buttress or which occur at intervals shall be provided to prevent the buildup of hydrostatic pressure. The details of subdrains shall be provided by the soils engineer.
   (d)   Safety factor. The buttress fill shall be designed for a minimum safety factor of 1.50 based upon the smaller value of yield or ultimate shear strength of the fill material.
(§ 2, Ord. 156-NS, eff. August 27, 1970, as amended by § I, Ord. 534-NS, eff. June 19, 1975)