20 SW EVERETT MALL WAY Geotech Report 2018-01-02 MF Import

Campbell-F�eury Investments/Mallwest Center W-3103-1 9 April 1986 Page 9 be pl aced beneath the sl ab. If the base of the fl oor sl ab i s set at or bel ow — adjacent outside grade, a periReter footing drain will be required around the building. 4.6 Permanent Slopes and Retaining Structures We recommend that permanent cut slopes above the ground water table be designed for a maximum inclination of 2H:1V. If seepage zones are encountered in cut slopes, a perforated drain pipe or rock facing may be required to reduce erosion and piping. � Fill slopes should also be constructed at a maximum inclination of 2H:1V. The surface of the fill embankment should be compacted to the same 90 percent density "' (ASTM:D 1557) as the body of the fill. This may be accomplished by overbuilding the embankment and cutting it back to its compacted core. The cut-away material -- should be placed as structural fill elsewhere. Alternatively, the surface of the slope may be compacted as it is built: All slopes should be protected from runoff �_ by diversion berms or swales, and if necessary, an impervious cover. Perinanent slopes should also be seeded and/or planted to gain erosion control. ^ If slopes steeper than 2H:1V are required locally, due to space limitations, they should be structurally retained. If limited maintenance can be tolerated, a "rockery" wall could be used to protect the cut face on an otherwise stable, natural or filled slope. If a rockery is selected, it should be constructed according to Snohomish County requirements. We recommend that rockeries be constructed of sound, - durable stone with a batter of no steeper than 6V:1H. The bottom course of each rockery should be founded on at least medium dense, native or structural fill soils _, and set into a 24-inch deep "key". The long dimension of the rock should be set perpendicular to the face of the wall. A 4-inch minimum diameter perforated drain pipe should be installed behind the first rockery course and be fully embedded in washed rock or pea gravel. As the rocks are being placed, a 2- to 4-inch quarry ;� spall backfill should be placed so that adequate drainage is maintained behind the " rockery. Rockeries greater than 6 feet in height should only be constructed under a full-time observation of a qualified geotechnical engineer.