3716 UPLAND AVE 2018-03-27 - Laserfiche WebLink

} Jesse Jerabek JN 15044 March 30, 2015 Page 2 CONCLUSIONS AND RECOMMENDATIONS GENERAL Our exploration at the site found very dense, cemented, native silty sands(Glacial Till)underlying 3 to 5 feet of loose fill and weathered soils. The dense to very dense glacial till soils encountered in our hand borings would be considered stable at the site grade inclinations. Based on our explorations, the new house can be supported by conventional foundations bearing directly on the dense native till soils. For all footings other than the western edge footings, structural fill may be placed between the footings and bearing soils as long as the fill is properly placed and compacted in accordance with the recommendations in this report. However, due to the slope on the west side of the house, we recommend excavating all of the proposed footings on the western edge of the proposed structure to bear directly on the dense till soils. The proposed structure setback of 40 feet from the steep slope is acceptable from a slope stability standpoint. These measures will be sufficient to protect the proposed addition from anticipated slope instability and will prevent the addition from having any effect on the slope stability. No fill should be placed on or within 20 feet of the site slopes since the added weight of the fill soils could reduce the stability of the slope. The site soils on the upland portion of the site and topography are not suitable for infiltration of surface water. The downspouts and surface drains should be tightlined to a suitable outfall away from the top of any slopes. The on-site sand soils are silty, and thus are moisture-sensitive. The silty sand soils can be reused as structural fill, provided that they are placed in dry weather and are at, or near, the optimum moisture content. The silty sand soils should not be placed in contact with foundation walls. The erosion control measures needed during the site development will depend heavily on the weather conditions that are encountered. While site clearing will expose a large area of bare soil, the erosion potential on the site is relatively low due to the gentle slope of the ground. We anticipate that a silt fence will be needed around the downslope sides of any cleared areas. Existing catch basins in, and immediately downslope of, the planned work areas should be protected with pre-manufactured silt socks. Cut,slopes and soil stockpiles should be covered with plastic during wet weather. Any disturbance to the existing slope outside of the building limits may reduce the stability of the slope. Damage to the existing vegetation and ground should be minimized, and any disturbed areas should be revegetated as soon as possible. Any disturbance of the vegetation on the steep slope should only be completed in small areas as part of an approved revegetation plan that incorporates drought-tolerant plantings with deep root systems. No irrigation systems should be placed on or directly above the steep slope. We recommend that Geotech Consultants, Inc. be afforded the opportunity to review the development plans, to amend our recommendations as necessary, and to verify that the recommendations presented in this report are adequately addressed in the design. Such a plan review would be additional work beyond the current scope of work for this study, and it may include revisions to our recommendations to accommodate site, development,and geotechnical constraints that become more evident during the review process. We recommend including this report, in its entirety, in the project contract documents. This report should also be provided to any future property owners so they will be aware of our findings and recommendations. SEISMIC CONSIDERATIONS In accordance with the International Building Code (IBC), the site soil profile within 100 feet of the ground surface is best represented by Soil Profile Type D (Stiff Soil). As required by the SBC, the design criteria presented in this report consider the effects of a one-in-100-years seismic event for slope stability. GEOTECH CONSULTANTS,INC.