2721 WETMORE AVE MARQUEE APARTMENTS 2023-06-28

Subsurface Exploration, Geologic Hazard, and 2721 Wetmore Preliminary Geotechnical Engineering Report Everett, Washington Preliminary Design Recommendations Soil nailing reinforcement is conducted by excavating vertically from the top down in stages of approximately 4 to 6 feet. After each stage of excavation, the exposed soils along the limits of the excavation are reinforced prior to proceeding with the next stage of excavation. Construction of a soil nail wall typically involves the following major steps: 1. Drill and install perimeter face stabilization elements, if needed; 2. Excavate soil, typically a 6-foot lift, leaving a small berm in place at the excavation toe; 3. Drill for nail holes; 4. Install and grout nails; 5. Excavate out berm to form vertical cut face; 6. Place drainage mat against cut soil face and protect with plastic sheeting; 7. Place waterproofing (if specified); 8. Place reinforcements, bearing plates, and studs; 9. Apply shotcrete wall; and 10. Repeat process down to final excavation grade. Consequently, this method requires that the soil withstand short-term, temporary vertical cuts of approximately 6 feet without caving. The glacially consolidated sediments that were encountered in our exploration borings are suitable for this type of construction, provided they remain unsaturated. As previously discussed, localized groundwater seepage was encountered within the advance outwash underlying the site and similar localized areas of seepage may also be encountered within the lodgement till. Control of this seepage is vital to the success of soil nail shoring for this project. The sand must be maintained in a dewatered condition to safely achieve the vertical cuts required for soil nail wall construction. We anticipate that the soils below minor seepage zones, if present, will generally remain standing over the required cut height, but some sloughing or piping should be anticipated. Open cuts should not be allowed to stand unshored for more than 3 days. This time could be less if zones of fractured or slickensided soil or groundwater seepage are encountered. Open-face cuts should not be left open over weekends or holidays. After applying the first lift of shotcrete, the next lift can be built after 4 days or once the shotcrete has attained 50 percent of its design strength. The project shoring designer should verify this recommended interval between lifts and provide additional or alternative recommendations, if necessary. A series of load tests must be performed to verify the design and ultimate skin friction or adhesion of the soil nails. Two types of testing should be accomplished for soil nailing. An initial verification test program is performed prior to wall construction to verify that the design adhesion values are correct. Common verification testing programs consist of at least two 200-percent tests of the design or allowable load in the soil for each excavation wall. Verification testing is usually accomplished by loading each nail in 25-percent increments held for 5 minutes up to the final load of 200-percent design load. Creep measurements are May 28, 2019 ASSOCIATED EARTH SCIENCES,INC. FSM/Id-190168E001-2-Projects‘20190168\KE\WP Page 14 18185E Page 9 of 180