4808 BELVEDERE AVE 2016-01-01 MF Import

Timberbuild Homes JN 05357 September 20, 2005 Page 6 The values given above are to be used to �iesign permanent foundation and retaining walls only. It is nct appropriate to back-calculate soil strength parameters from the earth pressures and soil unit weights presented in the table. The passive pressure given is appropriate for the depth of level structural fill placed in front of a retaining or founda;ion wall only. The values for friction and passive resistance are ultimate values and do not include a safety factor. We recommend a safety factor of at least 1.5 for overtuming and sliding, when using the above values to design the walls. Restrained wall 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 amount of cracking that can occur where a wall is restrained by a c��rner. The design values given above do not include the effects of any hydrostatic pressures behind the walls a�d assume that no surcharges, such as those caused by slopes, vehicles, or adjacent foundations will be exerted on the walls. If these conditions exist, those pressures should be added to the above lateral soil pressures. Where sloping backfili is desired behind the walls, we will need to be given the wall dimensions and the slope of the bac�ll in arder to provide the appropriate design earth pressures. The surcharge due to traffic loads behind a wall can typically be accounted for by adding a uniform pressure equal to 2 feet multiplied by the above active fluid density. Heavy construction equipment should not be operated behind retaining and foundation walls within a distance equal to the height of a wall, unless the walls are designed for the additional lateral pressures resulting from the equipment. The wall design criteria assume that the backiill will 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 dunng compaction. Foundatlon/Retainlna Wall BacMlll and Waterarooflnc Backfill placed behind retaining or foundation walls should be coarse, free-draining structural fill containing no organics. This bac�ll should contain no more than 5 percent silt or clay particles and have �o 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 such as Miradrain 6000 or equivalent should be placed against the backfilled foundation and retaining walls. The drainage composites should be hydraulically connected to the foundation drain system. Free-draining backfill or gravel should be used (or the entire width of the backfill where seepage is encountered. For increased protection, drainage composites should be placed along cut slope faces, and the walls should be backfilled entirely with free-draining soil. The later section entitled Drainage Considerations should also be reviewed for recommendations related to subsurface drainage behind foundation and retaining walls. 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 shouid 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 surtace water to percolate into the backfill. The section entitled Genera/ Earthwork and Sbuctura/ Flll contains recommendations regarding the placement and compaction oi structural fill behind retaining and foundation walls. GEOTECH CONSULTANTS, iNC.