3000 41ST ST Geotech Report 2025-12-31

PNW Home Builders, LLC ES-2598.03 May 2, 2013 Page 10 Excavations and Slopes The Federal Occupation Safety and Health Administration (OSHA) and the Washington Industrial Safety and Health Act (WISHA) provide soil classification in terms of temporary slope inclinations. Based on the soil conditions encountered at the boring locations, fill encountered in the upper.. approximately 11 to 20 5 feet below existing grades or where groundwater seepage is exposed are classified as Type C by OSHA/WISHA. Temporary slopes over four feet in height in Type C soils must be sloped no steeper than 1.,5H:1V (Horizontal Vertical). The presence of perched groundwater may cause caving of the temporary slopes due to hydrostatic pressure. ESNW should observe site excavations to confirm the soil type and allowable slope inclination; If the recommended temporary slope inclination cannot be achieved, temporary shoring may be necessary to support excavations. Permanent slopes should maintain a gradient of 21-1:1V, or flatter, and should be planted with vegetation to enhance stability and to minimize erosion. A representative of ESNW should observe temporary and permanent slopes to confirm the slope inclinations are suitable for the exposed soil conditions, and to provide additional excavation and slope recommendations, as necessary. Pavement Sections The performance of site pavements is largely related to the condition of the underlying subgrade. To ensure adequate pavement performance, the subgrade should be in a firm and unyielding condition when subjected to proofrolling with a loaded dump truck. Structural fill in pavement areas should be compacted to the specifications detailed in the "Site Preparation and Earthwork"section of this report. It is possible that soft, wet, or otherwise unsuitable subgrade areas may still exist after base grading activities'. Areas containing unsuitable or yielding subgrade conditions will require remedial measures such as overexcavation and suitable structural fill placement prior to pavement. For lightly loaded pavement areas subjected primarily to passenger vehicles, the following. preliminary pavement sections can be considered: •. Two inches of asphalt concrete (AC), placed over four inches of crushed rock base. (CRB), or; • Two inches of AC placed over three inches of asphalt treated base (ATB). For relatively high volume, heavily loaded pavements subjected to occasional truck traffic, the following pavement sections can be considered: •. Three inches of asphalt concrete (AC) placed over six inches of crushed rock base (CRB), or;. • 'Three inches of AC placed over four inches of asphalt treated base (ATB). Earth Solutions NW,LLC