11611 AIRPORT RD Geotech Report 2018-01-02 MF Import

, t ^. Geo[echnical Engmcering Rcport Proposcd Ahn W�rehouse May I l, 2001 CG File No. 1 l21 Page I I Retaining Wall Design Values The lateral earth pressure acting on retaining walls is dependent on the nature and density of the soil behind the wall, the amount of lateral wall movement, which can occur as backfill is placed, and the inclination of the backfill. Walls that are free to yield at least one-thousandth of the height of the wall are in an "active" coudition. Walls restrained from movement by stiffness or bracing are in an "at-resP' condition. Active earth pressure and at-rest eaRh pressure can be calculared based on equivalent fluid density. Equivalent fluid densi[ies for acti:•e and at-rest earth pressure of 35 pounds' per cubic fooi (pcQ and 55 pcf,respectively, may be usrd for design for a level backslope. These values assume tha[ the on-site soils or imported granular fill are used for backfill, and that Ihe wall backfill is drained. The preceding values do not include the effects of surcharges, such as due to foundation loads, traffic or other surface loads'. Surc}�arge effects should be considered where appropriate. The 3bove lateral preseures may be resisted by fiiction at the base of the wall and passive resistance against the foundation. A coefficient of friction of 0.45 may be used to determine the base friction in Ihe native blacial soils. An equivalant fluid density 300 pcf should be used for passive resistance design. To achieve this value of passive pressure, the foundations should be poured "neaY' against the native dense soils, or compacted fill should be used as backfill against the front of the footing, and the soil in front of the wall should extend a horizontal distance at least equal to three times the foundation depth. We recommend that the upper 1 foot of soil be neglected when determining the passive resistance unless covered with a slab-on-grade. All wall backtill should be well compacted. Care should be taken to przvent the buildup of excess lateral soil pressures due to overcompaction of the wall backfill. This can be accomplished by placing wall backfill in 8-inch loose lifts and compacting with small, hand- operated compactors. Permanent drainage systems should be installed for retaining walls. We recommend that these drainage systems consist of an l8-inch-wide zone of cleen (less than 3 percent fines), free- draining granular material placed along the back of the wall. Pea gravel is an acceptable drain material. The granul�r matenal should bc placed up the back of the wall to within 1 foot of the ground surfacc. Drrmage composite may he used in place of the 18-inch wide zone of free- Cornerstone Geotechnical, Inc. �/ ��' �� I ,i