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7 r <br /> Geotechnical Engineering Evaluation NGA File No,983917 <br /> Stadium Flowers Addition March 10,2017 <br /> Everett,Washington Page 6 <br /> should be covered with plastic sheeting during wet weather. Disturbed areas should be planted as soon as <br /> practical, and the vegetation should be maintained until it is established. The erosion potential for areas <br /> not stripped of vegetation should be low. <br /> Site Preparation and Grading <br /> After erosion control measures are implemented, site preparation should consist of stripping the <br /> development areas of paved surfaces, organics, undocumented fill, and loose soils to expose medium <br /> dense or better native glacial soils for the structural fill subgrade, and in foundation, slab, and pavement <br /> areas. Our explorations generally encountered medium dense or better native soils approximately 1.6 to <br /> 2.4 feet below the existing ground surface within the excavation, corresponding to depths of <br /> approximately 2.4 to 6.4 feet below the projected surface of the asphalt or concrete existing throughout <br /> the site. However, additional stripping may be required if thicker layers of undocumented fill, loose soil, <br /> or organic materials are encountered in unexplored areas of the site. The stripped materials should be <br /> removed from the site or be stockpiled for later use as landscaping fill. The exposed subgrade should be <br /> compacted to a non-yielding condition. We recommend that any fill encountered in the structure and <br /> pavement areas be removed and replaced with structural fill or rock spalls extending to competent native <br /> material. Excavations near property lines should be sloped back for stability. Sloping ground to receive <br /> fill should be benched for added stability. The benches should be level and be a minimum of six feet <br /> wide. All permanent cuts and fills should be retained using engineered retaining walls approved by NGA. <br /> If significant surface water flow is encountered during construction, this flow should be diverted around <br /> areas to be developed and the exposed subgrade maintained in a semi-dry condition. This may require <br /> dewatering systems or sump and pumps to remove the seeping water from the excavations. If wet <br /> conditions are encountered, alternative site stripping and grading techniques might be necessary. These <br /> could include using large excavators equipped with wide tracks and a smooth bucket to complete site <br /> grading and covering exposed subgrade with a layer of crushed rock for protection. If wet conditions are <br /> encountered or construction is attempted in wet weather, the subgrade should not be compacted, as this <br /> could cause further subgrade disturbance. In wet conditions, it may be necessary to cover the exposed <br /> subgrade with a layer of crushed rock as soon as it is exposed to protect the moisture sensitive soils from <br /> disturbance by machine or foot traffic during construction. The prepared subgrade should be protected <br /> from construction traffic and surface water should be diverted around prepared subgrade. <br /> NELSON GEOTECHNICAL ASSOOIATES, INC <br />