600 54TH ST SW I Geotech Report 2025-01-29

GEOTECHNICAL INVESTIGATION EVERETT,WASHINGTON March 2,2018 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. 8.1.8 Groundwater Influence on Construction At the time of our investigation,groundwater was encountered in several of the test pits. Approximate depth to groundwater in these test pits are as follows: Test Pit Depth to Groundwater TP-4 3&6 feet TP-5 3 feet TP-6 4 feet TP-7 2.5 feet TP-8 7 feet Groundwater was not encountered in the other test pits during our evaluation. We anticipate that typical sump excavations and pumping will adequately de-water trenches and other shallow excavations. Their design should be provided by the contractor. 8.1.9 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 8 and a modulus of subgrade reaction value of k= 18o 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 loose soils are present.The depth to suitable soils in these areas will likely vary and may require overexcavation, geotextile placement,and replacement with suitable fill up to subgrade. Site-specific recommendations should be provided during construction. The subgrade should be compacted to at least 95 percent of the maximum dry density as determined by ASTM Test Method D1557. In place density tests should be performed to verify proper moisture content and adequate compaction. However,if the subgrade soil consists of firm and unyielding native glacial soils a proof roll of the pavement subgrade soil may be performed in lieu of compaction tests. The recommended flexible and rigid pavement sections are based on design CBR and modulus of subgrade reaction(k)values that are achieved,only following proper subgrade preparation. It should be noted that subgrade soils that have relatively high silt contents will likely be highly sensitive to moisture 11