1318 37TH ST 2018-01-02 MF Import

James Pirie �' JN 97 March 18, 1997 e 7 Page 7 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 Backfil! 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. If the native sand is used as backfill, a drainage composite similar to Miradrain 6000 should be placed against the backfilled retaining walls. The drainage composites should be hydraulically connected to the foundation drain system. 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 wall 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 impermeable soil or topsoil, or the surface should be paved. The ground surface must also slope away from backfilled walls to reduce the potential for surface water to percolate into the backfill. The sub -section entitled General Earthwork and Structural Fill contains recommendations regarding the placement and compaction of structural 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 should be provided. This could include limiting cold -joints and wall penetrations, and possibly using bentonite panels 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 Excavation slopes should not exceed the limits specified in local, state, and national government safety regulations. Temporary cuts to a depth of about 4 feet may be attempted vertically in unsaturated soil, if there are no indications of slope instability. Based upon Washington Administrative Code (WAC) 296, Part N, the dense, silty sands at the subject site would be classified as Type A. Therefore, temporary cut slopes greater than 4 feet in height cannot be excavated at an inclination steeper than 0.75:1 (Horizontal:Vertical). Cut slopes in the loose to medium -dense soils should be no steeper than 1:1 (H:V). The above -recommended temporary slope inclinations are based on what has been successful at other sites with similar soil conditions. Temporary cuts are those that will remain unsupported for a relatively short duration to allow for the construction of foundations, retaining walls, or utilities. Temporary cut slopes should be protected with plastic sheeting during wet weather. The cut slopes should also be backfilled or retained as soon as possible to reduce the potential for instability. Please note that loose soil can cave suddenly and without warning. Utility contractors should be made especially aware of this potential danger. 2_0 GEOTECH CONSULTANTS, INC.