1584 E Santa Clara Ave - Soils Report

Home Browse Search

11932.003 Review of Sheet 4 of 8 indicates a short retaining wall (3 feet tall) at the rear of Lots 13 and 14 with a minor 2:1 (horizontal:vertica l) slope ascending beyond the wall to the residential lots behind Lots 13 and 14. These walls were added to the plans as part of the Delta 1 revision. lt was noted that the previous geotechnical investigation report for the project by Alta (2015) did not include geotechnical design recommendations for sloped backfill above retaining walls; therefore, we are providing supplemental geotechnical recommendations in this letter to support design of the proposed retaining walls associated with Lot Nos. 13, 14 and 16. lt is our understanding that the retaining walls shown on the plans along the southern boundary of the development and the short section of retaining wall along the western boundary at Lot 2 have already been constructed. PLAN REVIEW ANO RECOMMENDATIONS Based on our review, the reviewed precise grading plan set is considered acceptable from a geotechnical standpoint provided the following recommendations are incorporated with regard to the design of the planned retaining walls and driveway pavement for the project: Desiqn Recommendations for Retaininq Walls Review of precise plans indicates the planned retaining walls are typically 3 to 4 feet in height. The wall along Lots 13 and 14 is located at the back of the lots with the adjacent properties being somewhat higher in elevation. The wall along Lot 16 is located along the western side of the lot with the lot being somewhat higher in elevation than the adjacent street and sidewalk right-of way. Backfill Retaining structures planned al the site should be backfilled with granular (SE > 30), very low expansive (El < 20) free-draining soil throughout the zone of lateral pressure influence. All backfill should be mechanically compacted in layers; flooding should not be permitted. Proper compaction of backfill will be necessary to minimize settlement of the backfill and to minimize settlement of overlying slabs, concrete flatwork, and paving. Backfill should be compacted to at least 90% of the maximum dry density obtained by ASTM Test Method D1557. The excavated soils may be used in the compacted backfill; however, cobbles larger than six inches in diameter should be omitted from the backfill to minimize possible damage to the walls. Also, cohesive soils with significant clay content should not be used for backfill behind walls. The soils used in the upper foot of the backfill zone are recommended to consist of low expansive onsite soils. 2 € Leighton