215 DORN AVE Geotech Report 2022-10-25

Geotechnical Engineering Evaluation NGA File No. 1031018 Multi-Family Residential Development April 19,2018 Everett,Washington Page 6 Site Preparation and Grading After erosion control measures are implemented,site preparation should consist of removing loose soils, topsoil, and any undocumented fill from foundations,slab, and pavement areas,to expose medium dense or better native soils at depth. 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 at approximately one to three feet within the future building and associated pavement areas. We should note that additional deeper areas of unsuitable soils and/or undocumented fill could be encountered in unexplored areas of the site. This condition, if encountered, would require deeper excavations in foundation,slab,and pavement areas to remove the unsuitable soils. After site preparation, if the exposed subgrade is deemed loose,it should be compacted to a non-yielding condition and then proof- rolled with a heavy rubber-tired piece of equipment. Areas observed to pump or weave during the proof- roll test should be reworked to structural fill specifications or over-excavated and replaced with properly compacted structural fill or rock spalls. If loose soils are encountered in the foundation areas,the loose soils should be removed and replaced with rock spalls. 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. If wet conditions are encountered, alternative site grading techniques might be necessary. These could include using large excavators equipped with wide tracks and a smooth bucket to complete site grading, and covering exposed subgrade with a layer of crushed rock for protection. If wet conditions are encountered or construction is attempted in wet weather, the subgrade should not be compacted, as this could cause further subgrade disturbance. 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 subgrade should be protected from construction traffic and surface water should be diverted around areas of prepared subgrade. Temporary and Permanent Slopes Temporary cut slope stability is a function of many factors, including the type and consistency of soils, depth of the cut, surcharge loads adjacent to the excavation, length of time a cut remains open, and the presence of surface or groundwater. It is exceedingly difficult under these variable conditions to estimate a stable,temporary,cut slope angle. Therefore,it should be the responsibility of the contractor to maintain safe slope configurations at all times as indicated in OSHA guidelines for cut slopes. The following information is provided solely for the benefit of the owner and other design consultants and should not be construed to imply that Nelson Geotechnical Associates,Inc.assumes responsibility for job site safety. Job site safety is the sole responsibility of the project contractor. NELSON GEOTECHNICAL ASSOCIATES, INC. 89