1110 RAINIER AVE A DOMESTIC VIOLENCE SERVICES OF SNO CO 2018-01-01 MF Import

� Everatt Housing Fl ufhority M2y 16, 2012 � JN 12080 Pac,e 7 The vaiues given above are to be used to design only permanent foundation and retaining walls that are to be backfilled, such as conventional �valls constructed of reinforced concrete or masonry. It is not appropriate to use the above earth pressures and soil unit eveight to back-calculate soil strength parameters for design of other types of retaining walls, such as soldier pile, reinForced earth, modular or soil nail walls. We can assist �vith design of these types of walls, if desired. The passive pressure given is appropriate only for a shear key poured directly against undisturbed native soil, or for the depth of level, compact fill placed in front of a retaining or foundation wall. The values (or friclion and passive resistance are ultimate values and do not inc{ude a safety factor. We recommend a safety factor of at least 1.5 for overturning and sliding, when using the above values to design the walls. Restrained �vall soil parameters should be utilized for a distance of 1.5 times the wall height from corners or bends in the walls. This is intended to reduce the amo�nt of cracking that can occur where a wall is restrained by a corner. The design values given above do rot inciude the effects of any hydrostatic pressures behind the walls and assume that no surchar5es, such as those caused by slopes, vehicles, or adjacanl foundalions will be exerted on the ��•alis. If these conditions exist, ihose pressures should bo added to the above laleral soil pressures. Where sloping backfill is desired behind the walis, we �vill need to he given lhe wall dimensions and ihe slope oF the backfill in order to provide the appropriate design earih pressures. The surcharge due to lraKc loads behind a wall can lypically be accounted for by adding a uniform pressure equal to 2 feet multiplied by the above active (luid density. Heavy construction �quipment should not be operated behind relaining and foundation walls wilhin a distance equal to the height of a wail, unless the walls are designed tor the addl:ional Iaterai pressures resulting irom the equipment. Wall Piessures Due to Seismic Forces The surcharge wall Ioads that couid be imposed by ihe design earlhquake can be modeled by adding a uniform lateral pressure to lhe above-recommended active pressure. The recommended surcharge pressure is 8H pounds per square foot (psf), where H is lhe design reter�tion height of the wa11. Using this increased pressure, the safety factor against sliding and overturning can be recuced to 1.2 for the seismic analysis. Retaininq Wall Backfill and Waterproofinp Backfill placed behind retaining or foundalion �valls should be coarse, free•draining siructural (ill containing no organics. This backfill should contain no more lhan 5 percent silf 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. The later section entitlod Drainage Considerations should also be reviewed for recommendations relaled to subsurface drainage behind foundation and retaining walls. The purpose of these backfill requirements is lo e�sure that the design criteria for a retaining wall are not exceeded because of a build•up o( 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 shoutd be paved. The ground surface must also slope away from backiilled walls to reduce lhe potential for surface �vater to percolate into Ihe backfill. It is critical Ihat the wall backfill be placed in lifts and be properly compacted, in order for the above•recommended design earih pressures to be appropriale. The wall design criteria GEOTECH CONSULTANTS.INC.