909 51ST PL SW Geotech Report 2022-10-25

Geotechncial Engineering Evaluation NGA Project No. 1040218 Garcia Property Additions June 22, 2018 Everett, Washington Page 9 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. For planning purposes, we recommend that temporary cuts in the upper surficial weathered till and/or undocumented fill soils should be no steeper than 2 Horizontal to 1 Vertical (2H:1 V). Temporary cuts in competent, native soils at depth should be no steeper than 1.5H:IV. If significant groundwater seepage or surface water flow were encountered, we would expect that flatter inclinations would be necessary. We recommend that cut slopes be protected from erosion. The slope protection measures may include covering cut slopes with plastic sheeting and diverting surface runoff away from the top of cut slopes. We do not recommend vertical slopes for cuts deeper than four feet, if worker access is necessary. We recommend that cut slope heights and inclinations conform to appropriate OSHA/WISHA regulations. Permanent cut and fill slopes should be no steeper than 2HA V. However, flatter inclinations may be required in areas where loose soils are encountered. Permanent slopes should be vegetated and the vegetative cover maintained until established. Foundations Due to the anticipated depth of the unsuitable fill soils within the proposed development area, we recommend that the proposed structures be supported on a deep foundation system consisting of 4-inch pin piles to transfer structure loads down into the underlying competent materials and to maintain the effective setback. The piles should be driven to a minimum depth of 12 feet below the existing ground surface, and extend deep enough to provide a horizontal effective setback distance of 25 feet between the bottom of the pile and the face of the slope. We recommend that four -inch pipe piles be driven using a tractor -mounted hydraulic hammer, with an energy rating of at least 1,100 foot -lb. For this pile and hammer size, we recommend a design capacity of eight tons for each pile driven to refusal. The refusal criterion for this pile and hammer size is defined as less than one -inch of movement during 15 seconds of continuous driving at a rate of 550 blows per minute or higher. We recommend using galvanized schedule 40 pipe for the 4-inch pin piles. Maintaining these NELSON GEOTECHNICAL ASSOCIATES, INC.