2721 WETMORE AVE MARQUEE APARTMENTS Geotech Report 2023-06-22

Subsurface Exploration, Geologic Hazard,and 2721 Wetmore Preliminary Geotechnical Engineering Report Everett, Washington Preliminary Design Recommendations Caving could be experienced when excavating and installing lagging between piles. Overexcavation of soils should be avoided. Excavation should extend just far enough to allow lagging installation. Any void spaces behind lagging should be quickly identified and filled with pea gravel or other suitable free-draining material to prevent caving and loss of support for adjacent ground. Since the soldier pile wall system will also be designed as a permanent structural element for the proposed development, we recommend that corrosion protection be used for the structural elements of the wall designed to act as permanent structures. Corrosion protection requirements should be specified by the structural engineer. We also recommend that the seismic surcharges incorporated into the design of the permanent foundation elements of the development also be incorporated into the design of the wall structures planned as permanent structures. Drainage should be provided as recommended in this report. Due to its depth, the proposed excavation may require multiple rows of tieback anchors on three sides (west, north, and south). For multiple rows of tiebacks, a preliminary design pressure in the form of an "apparent" earth pressure distribution is recommended. We recommend an apparent earth pressure of 25(H+2) psf presented as a trapezoidal distribution where H is the retained excavation depth. The top of the distribution should be truncated from no pressure at the ground surface to full pressure at a depth of 10 feet. Refer to Figure 4 for additional design details and a graphic representation of the recommended apparent earth pressures. The apparent pressure distribution should be assumed to act over the tributary area of the piles above the excavation base and one concreted pile diameter below the base. The recommended earth pressure reflects surcharging from "normal" construction equipment and activities, as well as the variability of the site soils. A traffic surcharge equivalent to 2 feet of soil has been incorporated into the design-apparent earth pressures and is reflected in the H+2 portion of the apparent earth pressure. The use of apparent earth pressure for the shoring system assumes some minor deformation of the soil will occur. Typically, deformation on the order of 0.001 to 0.002 times the height of the excavation is possible. This could result in deflections on the order of about 0.25 to 0.5 inches for a 20-foot-tall wall. Theoretically, an equal amount of settlement occurs behind the wall. The settlement is typically greatest immediately adjacent to the wall and decreases with distance away from the wall. The limits of settlement are typically within a distance of one-half to one wall height behind the top of wall. Therefore, a comprehensive survey of the surrounding streets, structures, and other critical reference points should be performed prior to construction activities. These points should then be accurately monitored, as necessary, both horizontally and vertically, until the permanent walls and floors have been completed in the excavation. From a soil standpoint, the grouted soldier piles must be designed for sufficient vertical capacity, and should include the vertical component-of the inclined tieback loads. It should be noted that settlement of the soldier piles under load could also cause a reduction in anchor May 28,2019 ASSOCIATED EARTH SCIENCES, INC. FSM/Id-190168E001-2-Projects\20190168\KE\WP Page 17