5213 GLENWOOD AVE 2017-03-09 - Laserfiche WebLink

Revised Redi-Rock Retaining Walt Design Western Geotechnical Consultants,Inc. 52XX Glenwood Ave.Property #14 91 2 Everett,WA April 17,2015 Key elements in the construction of a stable wall include the following: • The wall must be founded on a stable foundation. The excavation for the wall should be inspected and probed by qualified personnel before the 6-inch thick gravel or concrete base is placed to ensure that our design assumptions are met and a there is uniform support for the base row of blocks. Based on our exploration of the site, we anticipate that the concrete or gravel base will be founded on undisturbed glacial till. • If the minimum 6" wall foundation base is constructed of crushed stone. the stone should meet the specifications of section 9-03.9(3) "crushed surfacing"of the Washington State Department of Transportation "Standard Specifications for Road, Bridge, and Municipal Construction". • Fill placement and compaction behind the wall should meet the criteria provided in the specifications or as indicated herein,(see Appendix E). When geogrid is placed it should he placed on a horizontal surface, Fill placed over the geogrid should also be placed on a level surface and it should be spread from the wall face back so as to put the geogrid in tension. • The contractor should also ensure that the geogrid is placed in the machine-direction as determined by the manufacturer to obtain the required reinforcement strength used in the design. Most gcogrids have significantly more strength in the machine direction than in the perpendicular direction (uniaxial) and our design assumes the maximum strength of the geogrid, which is in the machine direction. • Drainage is essential for proper performance of retaining walls. The wall design assumes drained conditions and does not allow for hydrostatic pressure buildup behind the wall. The design therefore requires a 1-foot thick layer of drain rock, pea gravel, or other material, as approved by the geotechnical engineer, placed directly behind the wall, with a rigid smooth- wall, 4-inch diameter perforated pipe at the base of the wall, as shown on the wall typical cross sections in Appendix A. • The select backfill must be properly placed and compacted on a level surface behind the wall. Backfill placed behind the wall should be placed on a horizontal surface in uniform lifts and be compacted to a dense and non-yielding condition. The fill should be placed in maximum S to 10 inch loose horizontal lifts and thoroughly compacted. Within the active zone behind the wall the fill should be compacted to 92 percent of the maximum dry density as determined by ASTM D-1557 test procedure. Backfill should be tested to ensure specified compaction is achieved. • The top approximate 1/2 to I-foot of ground behind the walls should be covered with a relatively impervious layer to minimize surface water infiltration. A separation geotextile (Amoco Fabrics, Pro Pex 45 35 or equivalent) should be placed between the Toner, more: pervious wall backfill and the overlying impervious material to minimize migration of the fine-grained material into the relatively free-draining wall backfill. The recommendations in this report are based on site conditions to the limited depth of site explorations performed by others and further assume that the exploratory data is representative of the subsurface conditions along the wall alignment. 7