2320 RAILWAY AVE INTERWEST CONSTRUCTION INC Geotech Report 2023-02-17

Interwest Construction Co.-Railway Avenue Improvements,Everett,WA Feb. 14,2019/Revised Feb. 7,2020 Geotechnical Engineering Report P1486-T18 111 Clearing and Stripping: After surface and near-surface water sources have been controlled, sod, topsoil,and root-rich soil should be stripped from the site. Organic soils are not present within the project area. Site Excavations: Based on our explorations,we anticipate that project excavations will encounter moderately to poorly consolidated granular soils,which can be readily excavated utilizing standard excavation equipment. Dewatering: Our explorations encountered groundwater seepage at a depth of approximately 7 to 10 feet below existing grade. The majority of the soils encountered onsite are silty,granular alluvial soils, which could potentially be water bearing during winter months. The contractor should be prepared to deal with this condition. For shallow excavations above the water table,should groundwater be encountered,we anticipate that an internal system of ditches,sump holes,and pumps will be adequate to temporarily dewater excavations. For deeper excavations below the water table,more extensive dewatering equipment, such as well points, could be necessary in order to temporarily dewater excavations. We recommend that the appropriate dewatering system be selected during construction, when the specific subgrade conditions encountered in the pipe trench are directly observable. The contractor should be prepared for more extensive dewatering at that time should it be needed. Temporary Cut Slopes: All temporary soil slopes associated with site cutting or excavations should be adequately inclined to prevent sloughing and collapse. Temporary cut slopes in site soils should be no steeper than 11H:1V, and should conform to Washington Industrial Safety and Health Act (WISHA) regulations. ' Subgrade Compaction: Exposed subgrades for the foundation of the proposed structures should be compacted to a firm, unyielding state before new concrete or fill soils are placed. Any localized zones of looser granular soils observed within a subgrade should be compacted to a density commensurate with the surrounding soils. In contrast,any organic,soft,or pumping soils observed within a subgrade should be overexcavated and replaced with a suitable structural fill material. Site Filling: Our conclusions regarding the reuse of onsite soils and our comments regarding wet- weather filling are presented subsequently. Regardless of soil type, all fill should be placed and compacted according to our recommendations presented in the Structural Fill section of this report. Specifically, building pad fill soil should be compacted to a uniform density of at least 95 percent (based on ASTM:D-1557). Onsite Soils: We offer the following evaluation of these onsite soils in relation to potential use as structural fill: • Existing Fill/Alluvial Soils: Underlying the existing vegetation and gravel base material, we encountered granular soils comprised of fine to medium sand with some to trace silt and abundant organics through a depth of±10 feet. This material ' Migizi Group, Inc. Page 7 of 13 r.ii,i i IIIII