1130 RAINIER AVE WHOLE SITE DOCUMENTS 2016-01-01 MF Import

� Evereff Housing Autliority hiay 16. 2012 � JN 12080 PaSe 7 The values given above are to be usetl to design only permanent foundation and retaining �valls that are to be backfilled, such as com�entional �valls constructed of reinforced concrete or masonry. It is not appropriate to use the above ear�h pressures and soil unit �veight to back-calculate soil strength parameters for design of olher types of retaining �valls, such as soldier pile, reinforced earth, modular or soil nail walls. We can assist with design of these types of v�alls, i( desired. The passive pressure given is appropriate orly for a shear key poured directly against undislurbed native soil, or for the depth o( level, compact fill placed in front of a retaining or fc�;ndafion �eall The values for friction and oassive resistance are ultimale values and do not include a safet, factor. We recommend a safery faclor of at least 1.5 for overtumin9 and sliding, �r:hen using (he above values lo design the walls. Restrained viall soil oaramelers should be utili�ed fo• a distancc of 1.5 times Ihe wail height (rom comers or bends in lhe walls. Tnis is intended lc rec'.uce fhe amount of cracking that can occur where a�vall is restrained �y a corner. The design values given above do not include the eifects of any hydrostatic pressures behind ihe �valls and assume ihat no surcharges, such as those caused by slupes, vehicles, or adjacent foundalions will be exerted on the �valls. If these conditions exist, ihose pressures should be added to the above lateral soil pressures. Where sloping back(ill is desired behind the �valls, we will need to be given lhe wall dimensions and the slope of the backfill in order to provide the appropriate design earth pressures. The surcharge due to lraffic loads behind a wall can typically be accoi:�ted tor by adding a uniform pressure equai to 2 feel multiplied by the above active fluid density. Heavy constniction equipment shouid not be operated behind retaining and foundation walls within a distance equal lo the height of a wall, unless the walis are designed for the additional lateral pressures resulling trom the equipment. Wall Pressures Due to Seismic Forces The surcharge wall loads that could be imposed by the design earthquake can be modeled by adding a uniform lateral pressure to the above-recommended active pressure. The recommended surcharge pressure is 8H pounds per square foot (ps(), where H is lhe design retention height of the �vall. Using this increased pressure, the safety factor agamst sliding and overturning can be reduced to 1.2 for the seismic analysis. Retaininq Wal! Backfilf end Waterproofinq Backfill placed behind retoining or foundalion walls should be coarse, free-draining struclural fill containing no organic;. This backfill should contain no more than 5 percent silt or clay particles and i�ave no gravei greafer than 4 inches in diametec The percentage of particles passing lhe No. 4 siove should be between 25 and 70 percent. The later section entitlod Drainage Considerations should also be reviewed for recommendations related lo subsurface drainage behind foundation and retaining walls. The purposo of these backfit! requirements is to ensure that the design criterla 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 consisl of a compacted, relatively impermeable soil or topsoil, or the surface should be paved. The ground surtace musl also slope away from back(illed walls to reduce the potential for surface water to percolate into lhe backfill. It is critical that the wall backfill be placed in lifts and be properly compacled, in order for the above-recommended design earth pressares to be appropriate. The wall design criteria GEO i ECH CONSULTl�NTS, INC.