204 E MAGNOLIA AVE 2016-01-01 MF Import

Allestad June 18, 1990 Retaining Walls Static design of basement walls structurally bracEd against movement should be based on an �equivalent fluid density of 50 pcf. This pressure assumes that the backfill is horizontal and cc,mposed of free-��raining granular material meeting the gradation requirements presented in "Site Grading" and that there is no water pressure behind the wall. Uniform lateral pressure due to a uniform vertical surcharge behind a braced wall should te computed using a coefficient of 0.45 times the uniform vertical surcharge load. Static design of permanent cantilevered retaining walls which support a 2:1 (h:v) slope surface of free draining backfill nay be based on an equivalant fluid density of 55 pcf. Cantilevered retaining walls should be expected to yield or move outward during and after backfilling, and such movements should be considered in design. Actual wall movements will depend on the wall design and method of backfilling. Estimated wall movements with proper backfilling methods can range from 0.1� to 0.2$ of the wall height. Conventional spread footing foundations founded on undisturbed natural glacial soils may be used for support of retaining walls. Design of wall foundations should be in accordance with the recommendations pr�sent�d in "Spread Footing Foundations" . Care should be exercised in conpacting backfill aqainst retaining walls. Heavy equipment should not approa�h retaining wr.11s close enough to intrude within a 1:1 line projected . :ward from the bottom of the wall. Backfill close to walls should be placed and compacted with hand- operated equi.pment. Recommendations `or placement of str.uctural fill are presented in the ��Site Grading�� section. Design wall pressures given above assume no water pressure behind the walls. We recommend that an adequate drain system be provided at the base of all retaining walls. As a minimum, wall drains should consist of a four-ix�ch diameter perforated PVC drain pipe placed in at least one cubic foot of drain gravel per lineal foot along the base of the wall. Drain gravel should meet the gradation requirements of the Washington State DOT Standard Specifications Section 9- 03 .12(4� . Imported granular fill used for. backfill of retaining walls should be capped with pavinq or 12 inches of onsite silty soils to reduce surface water infiltration. Page No. 6 Project No. 90-122-01