1321 COLBY AVE 1988 PARKING GARAGE AND MEDICAL OFFICE BUILDING Geotech Report 2018-01-02 MF Import

lir Everett General Hospital & Medical Center W-5557 29 March 1988 Page 7 The site soils consist predominantly of gravelly, silty sand, which appears Suitable for use as structural fill only during extended dry weather periods. The existing moisture contents within the depth of planned excavation appear to vary from optimum to several percent above optimum. Wetter portions of the soil would require drying back to optimum moisture content prior to use as structural fill . During wet weather or wet site conditions, the use of the on-site soils for structural fill is not recommended. The zones of sandy silt, and organic-rich topsoil encountered at depth are not recommended for structural fill use. Imported fill should consist I of well-graded sand or sand and gravel. Under wet conditions, imported fill should contain less than 5 percent fines, based by weight on the portion passing a U.S. No. 4 sieve. Typically, soils containing less than 5 percent fines can be compacted under a wide variety of weather and site conditions. 1 4.4 Slab-On-Grade Floor Slab-on-grade floors should be founded on compacted, prerolled native soils or structural fill, in accordance with our recommendations outlined in previous report sections. It appears necessary to remove portions of the existing soil below slab areas and replace with compacted structural fill. The depth of removal and replacement should generally extend to the bottom of old fi :l and organic-rich soil . We recommend that the floor slabs be underlain by a minimum thickness of at least 6 inches of clean, sandy gravel , crushed rock or pea gravel, to serve as a drainage layer, capillary break and working surface. The recommended 6-inch capillary break layer should contain less than 5 percent fines, by weight, when measured on the portion passing a U.S. No. 4 sieve. The material should contain a minimum of 50 percent by weight, larger than a No. 4 mesh sieve, with a maximum particle size of 1 inch. Below-slab drains are recommended in the office building, as described in the Drainage Considerations section of this report. 4.5 Basement and Retaining Walls Retaining walls and basement walls constru-ted to allow some deflection during backfill placement may be designed to resist an active lateral force equivalent to a fluid weight of 35 pcf (pounds per cubic foot). Walls that are restrained structurally or by stiffness from lateral movement during backfilling can be I •