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COBALT r GEOTECHNICAL INVESTIGATION 0EOSC1,ENCE5 EVERETT, WASHINGTON December 5, 2019 8a.7 Groundwater Influence on Construction Groundwater was not encountered in any of the explorations. There is a encountered.chance The depth to groundwater groundwater could be encountered above the unweathered_ glacial till, where would likely be 5 to 8 feet below grade, if present. If groundwater is encountered, -we anticipate that sump excavations and small diameter pumps systems .term excavations, if required. Any system should be designed by the will adequately de -water short contractor. We can provide additional recommendations upon request. 8.1.8 Utilities Utility trenches should be excavated according to accepted an o��ac or experienced in ring practices following OSHA (occupational Safety and Health Administration) standards, by The contractor is responsible for the safety of open trenches. Traffic and vibration adjacent to trench g of excavation side slopes should be avoided. walls should be reduced; cyclic wetting and dryin 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 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 percent of backfill placed in or adjacent to buildings and exterior slabs should be compacted to aleast 95trench centbackof the maximum dry density based on ASTM Test Method D1557• , The, upper5 utility placed in pavement areas should be compacted to at least 95 percent of the maximum dry densitybased on ASTM Test Method D1557. Below 5 feet, utility trench backfill in pavement areas should be compacted density based on ASTM :Test Method D1557. Pipe bedding . to at least 90 percent of to maximum dry t3' should be in accordance with the pipe manufacturer`s recommendations. The contractor is responsible for removing all water -sensitive soils from depth trenches location of the proposed backfill location and compaction requirements. Depending on thep 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, :procedures. 8a.9 Pavement Recommendations The near surface subgrade soils generally consist of silty sand with gravel. conditions). soils We estiare mate as goo for pavement subgrade material (depending on silt content and moisture hs the subgrade will have a California Bearing Ratio (CBR) value of io and a modulus of subgrade reaction value of k = 20o pci,,provided the subgrade is,prepared in general accordance with our recommendations. We recommend that at a minimum,12 inches of the existing subgrade material be moisture conditioned (as necessary) and re -compacted to prepare for the construction of pavement sections. Deeper levels of recompaction or overexcavation and replacement may be necessary in areas where fill and/or very poor (soft/loose) soils are present. 10 PO Box 82243 Kenmore,AVAl98028 rnhaltvPnra�gmail.com 2o6-331-1097