3214 BROADWAY Geotech Report 2022-10-25

American Property Development ES-0599.06 June 9, 2016 Page 13 Revised October 16, 2017 Excavations and Slopes The Federal and state Occupation Safety and Health Administration (OSHA/WISHA) classifies soils in terms of minimum safe slope inclinations. In our opinion, based on the soil conditions encountered during fieldwork for this site, the weathered native soils and existing fill encountered to depths of up to four feet to seven feet would be classified by OSHA/WISHA as Type B. Temporary slopes in Type B soils should be sloped at an inclination of at least 1 H:1 V, or flatter. In our opinion, the dense to very dense native soils below the weathered native soil and fill would be classified by OSHANVISHA as Type A and B. Temporary slopes over four feet in height in Type A and Type B soils should be sloped at an inclination no greater than 0.75H:1V or 1H:1V, respectively. With respect to the proposed building excavations, temporary slopes inclined at 0.5H:1V are feasible within the very dense silty sand with gravel glacial till deposits. The geotechnical engineer should observe the excavations to verify the appropriate allowable temporary slope inclination. If the above slope gradients cannot be achieved, temporary shoring may be required. Permanent slopes should maintain a gradient of 2H:1 V, or flatter, and should be planted with an appropriate species of vegetation to enhance stability and to minimize erosion. Seismic Considerations The 2015 International Building Code specifies several soil profiles that are used as a basis for seismic design of structures. The 2015 IBC recognizes ASCE for seismic site class definitions. If the project will be permitted under the 2015 IBC, in accordance with Table 20.3-1 of ASCE, Minimum Design Loads for Buildings and Other Structures, Site Class C, should be used for design. In our opinion, the site has a low susceptibility to liquefaction. The absence of a shallow groundwater table observed at the test sites, and the soil relative density observed throughout the test sites is the primary basis for this conclusion. Drainage The presence of excessive groundwater seepage is not expected in the general site and utility excavations. However, zones of perched seepage are possible and may produce moderate flow rates within the site excavations. Temporary measures to control groundwater seepage and surface water runoff during construction would likely involve interceptor trenches and sumps, as necessary. Based on groundwater seepage conditions observed at the test sites, we do not anticipate extensive dewatering of excavations will be necessary. At this time we do not anticipate a permanent sub-slab drainage system will be necessary for this project. However, the location and depth of groundwater seepage and zones of chronic groundwater are difficult to predict. Therefore, if unanticipated groundwater conditions are encountered, the geotechnical engineer should reassess the need for additional drainage below the slab during construction. Earth Solutions NW,LLC