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Mr. David Klein 5 October 7, 1998 <br /> GME Project No. 7940 <br /> We recommend that the geogrid be placed on the second and fifth <br /> courses . The geogrid behind the lowest wall should have a length of <br /> 7 feet . Therefore, two geogrid layers would be required behind the <br /> lowest tier wall . Geogrid length for the upper wall should be 3 <br /> feet . A layer of geotextile filter fabric should be placed along the <br /> inside back of the slabs . Within 1 foot of the back of the slabs we <br /> recommend placing a granular drainage layer consisting of sand and <br /> gravel, or 3/4 inch crushed rock. <br /> Wall Backfill <br /> The backfill over the geogrid behind the granular drainage layer may <br /> consist of excavated on-site non-organic soils, which we estimate <br /> would consist of sandy clay. The clay should be moisture conditioned <br /> to within 2% of the optimum moisture content as determined by the <br /> Standard Proctor compaction test, ASTM: D 698 . Excessively wet clay <br /> should not be used as backfill . The fill should be placed in loose <br /> lifts not exceeding 4 to 6 inches thick. Each lift should be <br /> compacted to at least 95% of the maximum Standard Proctor dry <br /> density. We recommend placing approximately 1 foot of compacted clay <br /> on top of the granular drainage layer behind the wall to reduce <br /> surface water infiltration. <br /> GME CONSULTANTS,INC. <br />