1910 W MUKILTEO BLVD Geotech Report 2022-10-25

Geotechnical Engineering Evaln i NGA File No. 1238721 Spencer Garage Addition February 11,2021 Everett,Washington Page 6 Erosion Control The erosion hazard for the on-site soils is interpreted to be slight to moderate for exposed soil's,'but actual erosion potential will be dependent on how the site is graded and how water is allowed to concentrate. Best Management Practices (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 stripped or disturbed areas. Silt fences and/or straw bales should be erected to prevent muddy water from leaving the site. Disturbed areas should be planted as soon as practical and the vegetation should be maintained until it is established. The erosion potential of areas not stripped of vegetation should be low. Site Preparation and Grading After erosion control measures are implemented,site preparation should consist of stripping the topsoil, undocumented fill and loose soils from foundation, slab, pavement areas, and other structural areas,to expose medium dense or better native bearing glacial soils.The stripped soil should be removed from the site or stockpiled for later use as a landscaping fill. Based on our-::observations, we anticipate stripping depths of 2.0 to 4.0 feet, depending on the specific locations. However, additional stripping may be required if areas of deeper undocumented fill and/or loose soil are encountered in unexplored areas of the site. After site stripping, 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 pavement areas, the loose soils should be removed and replaced with rock spalls or,granular structural fill. 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 stripping and 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 NELSON GEOTECHNICAL ASSOCIATES, INC.