SR 06:242 - Laserfiche WebLink

Marion Pavan Page 3 July 12, 2006 ROOll 2c. Engineered Fill - BGC recommends that if strippings are incorporated into the fill, that the mixture only be used in landscaping areas. BGC also indicates that loose fill lifts of 8 to 12 inches are routinely successful, and they have recommended a minimum 90% relative compaction for several projects in Pleasanton. No estimates of future differential settlements of fill placed using these standards are provided. CSA Comment - We agree with the use of a strippings/clean fill mix only in landscaped areas. With respect to lift thicknesses of 12 inches and 90% relative compaction below homes, we recommend grading plan approval if the Project Geotechnical Consultant provides estimates of future total and differential settlement below lots constructed on engineered fill. These estimates could then be considered by future lot-specific geotechnical engineers during foundation design. Monitoring of fill settlement over time should also be considered to assist with individual lot design. 2d, Cut and Fill Slopes - In our previous letter, we (CSA) asked for building setback recommendations away from the tops and bottoms of slopes. We also observed that based on the current grading plan, 3H:1V cut/fill slopes were shown, but that BGC's May 25, 2006 report indicated that 2H:1V slopes could be constructed if predominately granular materials were used. We noted that if 2H:1V fill slopes were subsequently recommended, slope stability analyses would be needed. BGC responded that our comments are noted, however, no fill slope gradients steeper than 3H:1 V are planned. CSA Comment - We recommend approval of the final grading plan if no slopes steeper than 3H:1V are planned, and if the Project Geotechnical Consultant provides building setbacks away from the tops and bottoms of slopes. 2e. Utility Trench Backfill - BGC considered non-permeable plugs in utility trench backfill, however, in their opinion plugs can have a tendency to force groundwater to daylight at the plugs. To drain groundwater out of storm drain trenches, BGC recommends u1stalling a 4-inch diameter, 10.foot long perforated pipe in Class 2 Permeable Material at the upstream ends of the catch basins, These drainage pipes would drain into the catch basins a few inches above the box invert elevation. BGC indicates that sewage lines tend to be deep, and tend not to be a cause of surfacing groundwater, and joint trench drainage or plugging tends to be problematic due to utility company backfill requirements. Consequently, the subdrain requirements apply only to storm drain pipelines. COTTON, SHIRES & ASSOCIATES, INC.