7100 HARDESON RD 2016-01-01 MF Import

Fisher 3 Sons, Inc. August 19, 1997 JN 9728� Page 8 dimensions and the slope of the backfill in order to provide the appropriate design earth pressures. The surcharge due to traffic loads behind a wall can typically be accounted for by adding a unifortn pressure equal to 2 feet mul6plied by the above adive fluid density. Heavy constniction equipment should not be operated behind retaining and foundation walls within a distance aqual to the height of a wall, unless the wails are designed for the additional lateral pressures resulting from the equipment. The wall design criteria assume that the backfill wili be well-compacted in lifts no thicker than 12 inches. The compaction of backfill near the walls should be accomplished with hand-operated equipment to prevent the walls from being overloaded by the higher soil forces that occur during compaction. Retaining Wall Bac�ll Backfill placed behind retaining or foundation walls should be coarse, free-draining, structural fill containing no organics. This backfill should contain no more than 5 percent silt or clay particles and have no gravel greater than 4 inches in diameter. The percentage of particles passing the No. 4 sieve should be between 25 and 70 percent. For increased protection, drainage composites should be placed along cut slope faces, and the walls should be backfilled with pervious soil. The purpose of these backfill requirements is to ensure that the design criteria for a retaining wail are not exceeded because of a build-up of hydrostatic pressure behind the wall. The top 12 to 18 inches of the backfill should consist of a compacted, relatively impertneable soil or topsoil, or the surface should be paved. The ground surface must also slope away from backfilled wails to reduce the potential for surface water to percoiate into the backfill. The sub-section entitled Generol Earthwork and Structurai Fill contains recommendations regarding the placement and compacGon of sWctural fill behind retaining and foundation walls. The above recommendations are not intended to waterproof the below-grade walls. If some seepage through the walls or moist conditions are not acceptable, damp-proofing or waterproofing shoutd be provided. This couid include limiting cold-joints and wall penetrations, and possibly using bentonite paneis or membranes on the outside of the walls. Applying a thin coat of asphalt emulsion is not considered waterproofing, but it will help to prevent moisture, generated from water vapor or capillary action, from seeping through the concrete. Excavations and Slopes No excavated slopes are anticipated other than for utility trenches. However, excavation slopes should not exceed the limits specified in local, state, and national govemment safety regulations. Temporary cuts to a depth of abaut 4 feet may be attempted vertically in unsaturated soil, if there are no indications of slope instability. Based upon Washington AdminisVative Code (WAC) 296, Part N, the soil type at the subject site would be Gassified as Type B. Therefore, temporary cut slopes greater than 4 feet in height cannot be excavated at an inclination steeper than 1:1 (Horizontal:Vertical), extending continuously between the top and the bottom of a cut. The above-recommended temporary siope inclination is based on what has been successful at other sites with similar soil conditions. Temporary cuts are those that will remain unsuppoRed for GEOIECH CONSULTAI�TS, MC.