4626 HARBOR LN 2018-01-02 MF Import

Gaotechnical Engineering Evaluation NGA File No.853512 Fox Residence Underpinning and Retaining Wall Design August 3, 2012 Everett, Washington Page G (BMPs) should be used to control erosion. Areas disturbed during construction should be protected from erosion. Erosion control measures may include diverting surface water away from the supped or disturbed areas. Silt fences and/or straw bales should be erected to prevent muddy water from leaving the site or Flowing down the sloping ground surface. Stockpiles should be covered with plastic sheeting during wet weather. Disturbed areas should be planted as soon as practical and the vegetation should be maintained until it is established. The erosion potential for areas not stripped of vegetation should be low. We recommend that the sloping ground outside of the development areas not be disturbed or modified through placement of any fill or removal of the existing vegetation. All till should be placed as structural fill. No additional material of any kind should be placed on sloping ground, such as excavation spoils, i vn clippings, and other yard waste, trash, and soil stockpiles. Landscaping areas and replacement of vegetation should be performed in accordance with the city code. Under no circumstances should water be allowed to concentrate on the sloping ground. Site Preparation and Grading After erosion control measures arc implemented and garage foundations have been successfully underpinned, site preparation should consist of removing loose soils, topsoil, and undocumented fill, to expose medium dense or better native soils in the plamred new wall area. The stripped soil should be removed from the site or stockpiled for later use as a landscaping fill. Based on our observations, we anticipate native, medium dense or better soil to be encountered approximately five to six feet in the location of the retaining wall. After site preparation, if the exposed subgrade is deemed loose, it should be compacted to a non -yielding condition. Areas observed to pump or weave during compaction should be reworked to structural fill specifications or over -excavated and replaced with properly compacted structural fill or rock spoils. If significant surface water flow is encountered during construction, this Flow should be diverted around areas to be developed, and the exposed subgrades should be maintained in a semi -dry condition. In wet conditions, it may be necessary to cover the exposed subgrade with a layer of crushed rock as soon as it is exposed to protect the moisture sensitive soils from disturbance by machine or foot traffic during construction. The prepared subgrde should be protected from construction traffic and surface water should be diverted around areas of prepared subgrade. NELSON GEOTECHNICAL ASSOCIATES, INC.