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 pre-stress, allowing lateral tilting about the base. For design purposes, the vertical load capacity should be determined based on an allowable adhesion or side friction of 2 kips per square foot (ksf), an allowable end bearing of 15 ksf for the temporary loading condition (lean-mix backfill), and 30 ksf for the permanent loading condition (concrete backfill). These allowable end-bearing conditions assume a minimum embedment of at least 10 feet below the base of the excavation. For computing bending moments in piles, 80 percent of the above earth pressures should be used. If groundwater seepage is encountered, we anticipate soldier extendingthrough the seepage zone(s) encountered in the borings mayrequire special piles g g q P soldier pile installation techniques, such as casing or drilling under a fluid head, to complete soldier pile installation. The contractor should be prepared to utilize casing or drilling fluids, as necessary, to complete soldier pile/tieback installation in the event that the borings will not otherwise remain open. The soldier piles also need to be located a sufficient depth below the base of the excavation to provide adequate lateral or "kick-out" resistance to horizontal loads below the lowest brace or tieback level. In this regard, the lateral resistance may be computed on the basis of passive pressure in the form of an allowable "passive" earth pressure equivalent to 350(D-2) psf where D is the depth of embedment below the base of the excavation in feet. This pressure may be considered to be acting against twice the diameter of the grouted soldier pile section. 13.3 Tieback Anchors For tiebacks used in the shoring system, the grouted anchors must be located far enough behind the soldier pile wall to develop anchorage within a stable soil mass to prevent system failure or excessive deformation. We recommend that this anchorage be obtained behind an assumed failure plane defined by a horizontal line extending a distance equal to H/4 behind the retained excavation at the base of the excavation, which then rotates 60 degrees from the horizontal and extends upward to the ground surface. The area between this assumed failure plane and the retained excavation is referred to as the "no load zone."These recommendations are presented on Figure 4. The anchor loads are transmitted to the surrounding soil by side friction or adhesion with the soil. Temporary tieback anchors completed using hollow-stem auger techniques within the natural sediments may be designed for an allowable shaft friction of 1,200 psf. Alternatively, for 6-inch-diameter, pressure-grouted anchors installed fully within glacially consolidated sediments, a shaft friction of 2,000 psf can be assumed. Assumed anchor design loads should be confirmed by proof-testing, as outlined subsequently. All anchors should be a minimum of 10 feet in length past the no load zone. Tieback anchors should be installed at an angle of at least 15 degrees below the horizontal. Care must be exercised when installing tiebacks to avoid existing utilities and foundations. As previously noted, the buildings north and south of the project area contain basement levels. Demonstration of utility and foundation protection will be required to obtain a temporary May 28,2019 ASSOCIATED EARTH SCIENCES,INC. FSM/ld-190168E001-2-Projects\20190168\KE\WP Page 18