5034 OCEAN AVE Geotech Report 2022-10-25

sediments that comprise the core of the slope. BGC,pllc will be available to provide geotechnical engineering special inspections during the development of the project and will address any unanticipated geotechnical conditions should they occur. Site Preparation Site preparation for construction of the planned new development will consist of removal of the existing vegetation from the building area. Other than the large trees that may need to be removed as part of future landscaping plans,the remaining vegetation outside of the building envelope should be left intact until after the foundation construction to provide erosion control cover during development. Soil from the foundation excavation area that will not be used as backfill should be removed from the site or may be placed as landscaping fill around the perimeter of the development area. All fill soil placed should be placed on horizontal benches cut into the sloping ground. Temporary cut slopes into the medium dense fill soils and dense sand for installation of the foundation should be sloped back to a 1I-1:1V inclination. For all utility excavations deeper than 4 feet should use a trench shield or also be sloped back during installation. Cut slope inclinations may be adjusted in the field to suit the weather and soil conditions at the time of excavation. Soil to be re-used onsite should be covered with plastic sheeting to reduce the potential for erosion and sediment transport and to maintain the water content of the excavated soil. Foundations Spread footing foundations may be used for foundation support of the planned additions to the single family residence. An allowable foundation bearing capacity of 2500 pounds per square foot may be . used for spread footings set to bear on the dense advance outwash sand sediments. A short term increase of one-third may be used for wind, snow, or seismic loads. In order to key the foundation into the slope, all footing shall be excavated a minimum of 4 feet below current grades to set the base of the footing a minimum of 2 feet into the dense sand. Anticipated settlement of the foundations placed as described should be less than 1 inch. BGC,pllc perform a foundation soil bearing evaluation prior to placing foundation concrete to verify that the prepared footing subgrade complies with the recommendations in this report. Lateral loads will be resisted by friction between the foundation and the supporting soils, and/or by • passive earth pressure acting on the buried portions of the foundations. The foundations must be backfilled with fill_compacted to a medium dense,non-yielding condition to achieve the passive resistance provided below. We recommend the following design parameters for lateral load calculations. • Passive equivalent fluid=250 pcf • Coefficient of friction=0.30 The above values are allowable and include a factor of safety of at least 1.5. Lateral Earth Pressure . • The concrete basement retaining walls should be designed to resist"at-rest"soil pressure conditions as the walls will be fixed at the top and not free to yield laterally at least 0.1 percent of their height. The walls should be designed using and equivalent fluid pressure of 50 pounds per cubic.foot(pcf). The basement walls should use either a full height chimney drain or approved drainage boards BGC, pllc 14267 209th Avenue NE Woodinville, WA 98077 (425) 273-5062