Appendix E - Geology and Soils Geotechnical Supporting Information COMBINED

LESTER-SHRINER PROPERTY 132-8-2 Page 13 liquefaction-induced settlement. This could involve supporting the new residential structures on more rigid mat foundations designed to tolerate increased total and differential settlement. Additional exploration and analysis should be performed during the design-level geotechnical investigation. 5.2 DESIGN-LEVEL GEOTECHNICAL INVESTIGATION The preliminary recommendations contained in this preliminary report were based on limited site development information, review of previous subsurface information by others, our recent site reconnaissance and supplemental exploration, and our experience in the area with similar projects. As site conditions may vary significantly between the explorations previously performed by others, we also recommend that we be retained to 1) perform a design-level geotechnical investigation, once detailed site development plans are available; 2) to review the geotechnical aspects of the project structural, civil, and landscape plans and specifications, allowing sufficient time to provide the design team with any comments prior to issuing the plans for construction; and 3) be present to provide geotechnical observation and testing during earthwork and foundation construction. SECTION 6: EARTHWORK 6.1 SITE DEMOLITION, CLEARING AND PREPARATION In proposed fill areas, the site should be stripped of all surface vegetation, and surface and subsurface improvements within the proposed development area. Since the site will likely include a significant amount of cut material to be removed from the site, it may be feasible to leave most surface vegetation since it will likely be blended with significant quantities of the underlying soil and bedrock materials during off-hauling. Where necessary, vegetation and topsoil should be stripped to a sufficient depth to remove all material greater than 3 percent organic content by weight, unless material is to be reused in future landscaping areas. 6.2 COLLUVIUM OVER-EXCAVATION As discussed in the “Conclusions” section, several areas of deeper colluvial soils have been encountered that will be susceptible to creep and potential slope instability. Although a significant portion of these weak materials will be excavated during mass grading for the site, the lower portions of the colluvial material could potentially creep or move downslope during the life of the project. Therefore, we recommend that colluvial material beneath proposed fills or extending beyond the limits of grading be over-excavated and replaced as an engineered fill buttress. If it is not feasible to over-excavate these materials, it may be necessary to stabilize the keyways with buried concrete stitch piers, subsurface drains and/or geosynthetic grids to reduce impacts from additional creep or downslope movement of the remainder of the landslide materials. Additional analyses should be performed during the design-level investigation to further evaluate the need and extent of any additional colluvial soil mitigation measures. The actual lateral extent and depth of all colluvial soils should be determined in the field by the Geotechnical Engineer during grading. Ii! CORNERSTONE EARTH GROUP