5109 SEAHURST AVE 2025-12-12 - Laserfiche WebLink

COBALT GEOTECHNICAL INVESTIGATION GEOSCIENCES EVERETT, WASHINGTON November 16,2018 We anticipate that sump excavations and small diameter pumps systems will adequately de-water short- term excavations within 8 feet of the ground surface. Any deeper excavations may require well points and water-tight shoring. Any de-watering system should be designed by the contractor. We can provide additional recommendations upon request. 8.1.8 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, sandy soils were encountered at shallow depths in the explorations at this site. These soils have low cohesion and density and will have a tendency to cave or slough in excavations. Shoring or sloping back trench sidewalls is required within these soils in excavations greater than 4 feet deep. 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 D1557. 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. 9.o Construction Field Reviews Cobalt Geosciences should be retained to provide part time field review during construction in order to verify that the soil conditions encountered are consistent with our design assumptions and that the intent of our recommendations is being met.This will require field and engineering review to: ■ Monitor and test structural fill placement and soil compaction ■ Observe foundation excavations ■ Observe slab-on-grade preparation Geotechnical design services should also be anticipated during the subsequent final design phase to support the structural design and address specific issues arising during this phase. Field and engineering review services will also be required during the construction phase in order to provide a Final Letter for the project. 8 PO Box 82243 Kenmore,WA 98028 cobaltpeo(@iimail.com 2o6-331-1097