11-10-1986 Council Packet - Laserfiche WebLink

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86-681 Tennis West, Ltd. -3- October 16, 1986 calculations indicate the 8-foot cross memb:r length can remain as proposed. In general, the upper wall, with the sloped backfill (assumed to be a 2:1 slope), will exhibit a factor of safety of about 2.0 as proposed. The active zone for this wall will intercept the hori- zontal plane at the top of the wall at 5 feet behind the wall or about 9 feet behind the wall on the slope. Again, the proposed anchors should extend behind this zone, but in order to reduce the amount of load exerted on the wall, we recommend the anchor length: be increased. As discussed previously, the upper two anchors should be increased to an embedment depth of 10 feet with the lower anchor at least 5 feet in length. As needed, addi- tional anchors should be at least 8 feet long. With the above modifications, it is our opinion that the factor of safety assuming soil- factors only will be at or above 2.0 which is the recommended minimum for a timber wall backfilled with cohesive soil. A_cached with this report is a sketch showing the configuration on which our analysis was conducted. Although our calculations indicate the wall can be safely constructed with the proposed soils, there are some risks in using clay material as backfill behind the retaining wall. Normally, it is recommended that the backfill be clean sand having less than 10% passing the #200 sieve. The purpose this is to provide a free -draining material behind the wall to prevent hydrostatic build-up against the walls. It should be noted that hydrostatic build-up was not included in our design analysis. Also, the use of a free -draining sand reduces the potential for frost related problems with the wall. As the upper wall is constructed, we recommend that, if feasi:'_e, the face of the cut be benched at various intervals to tie in the fill with the slope material. The backfilling operation must be carefully monitored. The fill should be placed in thin lifts and compacted to eliminate the potential for voids to exist within the backfill. GENERAL The analysis conducted was based on the assumption that the back - fill soils are predominantly clay. It is recommended that we be retained to observe the exposed natural soils and the filling operation to evaluate the actual soil characterist:.ics. We were not asked to evaluate the entire slope, only the stabi- lity of the walls. If the entire slope has noz been evaluated