11625 AIRPORT RD SONRISE CHRISTIAN CENTER Geotech Report 2022-10-25

I I GEOTECHNICAL EVALUATION EVERETT,WASHINGTON February 6,2018 8.1.5 Groundwater Influence on Construction Light to heavy groundwater seepage was encountered in TP-1 at 3 feet below grade,in TP-2 at 2 feet below grade,and in TP-4 at 2 feet below grade. Groundwater was not encountered in TP-3. The groundwater is perched between weathered and unweathered glacial till and is not likely present at the site during the dry season(generally June through September). If earthwork and utility placement occur when groundwater is present, we anticipate that 2 or 3-inch diameter pumps with sump excavations will be suitable to de-water utility excavations if they extend up to 8 feet below grade. Deeper excavations in sandy soils may require well points. Any system should be designed by a contractor or engineer with experience in their use and function. We can provide additional input upon request. 8.1.6 Utilities Utility trenches should be excavated according to accepted engineering practices following OSHA (Occupational Safety and Health Administration) standards, by a contractor experienced in such work. The contractor is responsible for the safety of open trenches. Traffic and vibration adjacent to trench walls should be reduced; cyclic wetting and drying of excavation side slopes should be avoided. Depending upon the location and depth of some utility trenches,groundwater flow into open excavations could be experienced,especially during or shortly following periods of precipitation. In general,silty and sandy soils were encountered at shallow depths in the explorations at this site. These soils have low cohesion and have a tendency to cave or slough in excavations. Shoring or sloping back trench sidewalls is required within these soils in excavations deeper than 4 feet. All utility trench backfill should consist of imported structural fill or suitable on site soils. Utility trench backfill placed in or adjacent to buildings and exterior slabs should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. The upper 5 feet of utility trench backfill placed in pavement areas should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method Di557. Below 5 feet,utility trench backfill in pavement areas should be compacted to at least 90 percent of the maximum dry density based on ASTM Test Method D1557. Pipe bedding should be in accordance with the pipe manufacturer's recommendations. The contractor is responsible for removing all water-sensitive soils from the trenches regardless of the backfill location and compaction requirements. Depending on the depth and location of the proposed utilities,we anticipate the need to re-compact existing fill soils below the utility structures and pipes. The contractor should use appropriate equipment and methods to avoid damage to the utilities and/or structures during fill placement and compaction procedures. 8.1.7 Pavement Recommendations The near surface subgrade soils generally consist of silty sand with gravel. These soils are rated as fair to good for pavement subgrade material (depending on silt content and moisture conditions). We estimate that the subgrade will have a California Bearing Ratio (CBR) value of 12 and a modulus of subgrade reaction value of k = 210 pci, provided the subgrade is prepared in general accordance with our recommendations. 7 PO Box 82243 Kenmore,WA 98028 (206)331-1097 Cobaltgeo0 gmail.com