6202 ASSOCIATED BLVD Geotech Report 2022-10-25

Proposed Everett Warehouse Project No. 2152.01 March 5, 2019 compaction will be impossible. Therefore, we recommend subgrade preparation and earthwork, in general, be completed during drier periods of the year when the soil moisture content can be controlled by aeration and drying. If earthwork or construction activities take place during extended periods of wet weather, or if the in situ moisture conditions are elevated above the optimum moisture content, the soils will become unstable and not compactable. In the event the exposed subgrade becomes unstable, yielding, or unable to be compacted due to high moisture conditions, we recommend that the materials be removed to a sufficient depth in order to develop stable subgrade soils that can be compacted to the minimum recommended levels. The severity of construction problems will be dependent, in part, on the precautions that are taken by the contractor to protect the subgrade soils. Once compacted, subgrades should be evaluated through density testing and proof rolling with a loaded dump truck or heavy rubber -tired construction equipment weighing at least 20 tons to assess the subgrade adequacy and to detect soft and/or yielding soils. In the event that compaction fails to meet the specified criteria, the upper 12 inches of subgrade should be scarified and moisture conditioned as necessary to obtain at least 95 percent of the maximum laboratory density (per ASTM D1557). Those soils which are soft, yielding, or unable to be compacted to the specified criteria should be over -excavated and replaced with suitable material as recommended in the Structural Fill section of this report. As an alternate to subgrade compaction during wet site conditions or wet weather, the upper 12 inches of subgrade should be overexcavated to a firm, non -yielding and undisturbed condition and backfilled with compacted imported structural fill consisting of free -draining Gravel Borrow or crushed rock. Freezing Conditions: If earthwork takes place during freezing conditions, all exposed subgrades should be allowed to thaw and then be compacted prior to placing subsequent lifts of structural fill. Alternatively, the frozen material could be stripped from the subgrade to expose unfrozen soil prior to placing subsequent lifts of fill or foundation components. The frozen soil should not be reused as structural fill until allowed to thaw and adjusted to the proper moisture content, which may not be possible during winter months. Structural Fill Materials and Preparation Structural fill includes any material placed below foundations and pavement sections, within utility trenches, to construct embankments, and behind retaining walls. Prior to the placement of structural fill, all surfaces to receive fill should be prepared as previously recommended in the Site Preparation section of this report. Laboratory Testing: Representative samples of on -site and imported soils to be used as structural fill should be submitted for laboratory testing at least 4 days in advance of its intended use in order to complete the necessary Proctor tests. Reuse of Site Soils as Structural Fill: We expect reuse of site soils will be desirable for general site grading and backfilling of underground utility excavations. The suitability for reuse of site soils as structural fill depends on the composition and moisture content of the soil. Soils encountered in excavations at the Page 7