PC-2026-15 - Laserfiche WebLink

330 Land Company, LLC Arroyo Lago 9785.004.001 Design-Level Geotechnical Report Page | 19 April 16, 2024 Latest Revision October 31, 2025 Jetting of backfill is not an acceptable means of compaction. We may allow thicker loose lift thicknesses, based on acceptable density test results, where increased effort is applied to rocky fill or for the first lift of fill over pipe bedding. 5.8 GRADED SLOPES In general, cut slopes less than 4 feet high and graded slopes less than 10 feet high should be no steeper than 2:1 (horizontal:vertical). All fill slopes should be adequately keyed into firm materials unaffected by shrinkage cracks. Fill slopes should be over-built and then trimmed back to finished grades. If a cut or cut-fill transition occurs within a graded slope, we recommend the slope be overexcavated and reconstructed as an engineered fill slope. The contractor is responsible for constructing temporary construction slopes in accordance with Cal/OSHA requirements. 5.9 SURFACE DRAINAGE The project civil engineer is responsible for designing surface drainage improvements. With regard to geotechnical engineering issues, we recommend that finish grades be sloped away from buildings and pavements to the maximum extent practical to reduce the potentially damaging effects of soil shrink and swell. The latest California Building Code Section 1804.4 specifies minimum slopes of 5 percent away from foundations within 10 feet for unpaved conditions. Where lot lines or surface improvements restrict meeting this slope requirement, we recommend that specific drainage requirements be developed. As a minimum, we recommend the following. 1. Roof downspouts should discharge into closed conduits and direct away from foundations to appropriate drainage devices. 2. Water should not be allowed to pond near foundations, pavements, or exterior flatwork. 5.10 STORMWATER BIOTREATMENT AND INFILTRATION We encountered moderately to highly expansive clay near the ground surface. Thus, the existing site soil is not expected to have adequate permeability for stormwater infiltration, unless subdrains are installed. We recommend assuming little stormwater infiltration will occur through the existing site soil. If bioretention areas are implemented, we recommend that, when practical, they be planned a minimum of 5 feet away from structural site improvements, such as buildings, streets, retaining walls, and sidewalks/driveways. When this is not practical, bioretention areas located within 5 feet of structural site improvements can either: 1. Be constructed with structural side walls capable of withstanding the loads from the adjacent improvements, or 2. Incorporate filter material compacted to between 85 and 90 percent relative compaction (ASTM D1557, latest edition) and a waterproofing system designed to reduce the potential for moisture transmission into the subgrade soil beneath the adjacent improvemen t.