200 W MARINE VIEW DR Geotech Report 2025-08-07

October 16,2020 Project No. T-8221 Preload Because of the uncertainty of the degree of wood waste contained in the fill and the soft compressible nature of the silt sediments below the fill, we recommend implementing a preload program. The preload program consists of placing required structural fill material over the building footprint and allowing the weight of this fill to pre- consolidate the compressible soils. The amount and rate of settlement is monitored, and once primary settlements have occurred,building construction can commence. The preload fill should extend a minimum of two feet beyond the edge of the perimeter building footings. If the amount of wood waste in the fill materials is consistent with that described in previous test pit and test boring explorations, we estimate that total settlement under the building preload fill will be in the range of two to four inches. It is estimated that 90 percent of the consolidation settlement will occur in about four to six weeks following full application of the preload fill. To verify the amount of settlement and the time rate of movement, the preload program should be monitored by installing settlement markers. The settlement markers should be installed on the existing grade prior to placing any building fill. Once installed, elevations of both the fill height and marker should be taken twice a week until the full height of the building fill is in place. Once the building fill is placed,readings should continue weekly until the anticipated settlements have occurred. Monitoring data should be forwarded to us within two days after it is obtained for review and comment. A typical settlement marker detail is shown on Figure 3. It is critical that the grading contractor recognize the importance of the settlement marker installations. All efforts must be made to protect the markers from damage during fill placement. It is difficult,if not impossible,to evaluate the progress of the preload program if the markers are damaged or destroyed by construction equipment. If the markers are impacted, it may be necessary to install new markers and extend the preload time period in order to ensure that settlements have ceased and building construction can begin. Potential long-term settlement due to secondary compression of the very soft silt and organic wood waste material may also occur. These secondary settlements cannot be fully mitigated during the surcharge program. The magnitude of this settlement will be greater in the early years diminishing with time. If the degree of wood waste is as indicated by the existing test pit and test boring explorations,we would not expect that the long-term secondary settlement would exceed one to two inches over the next 20 years. 5.3 Excavations All excavations at the site associated with confined spaces, such as utility trenches and lower building levels,must be completed in accordance with local, state, or federal requirements. Based on current Washington Industrial Safety and Health Act (WISHA) regulations, the upper fills and medium dense, native sands at the project site would be classified as Group C soils. Accordingly,temporary excavations in Type C soils should have their slopes laid back at inclinations no steeper than 1.5:1 (Horizontal:Vertical)from the toe to the crest of the slope. If there is insufficient room to complete the excavations in this manner, or if excavations greater than 20 feet in depth are planned, temporary shoring to support the excavations may be required. Properly designed and installed shoring trench boxes can be used to support utility trench excavations where required. Page No. 6