2721 WETMORE AVE MARQUEE APARTMENTS 2023-06-28

Subsurface Exploration, Geologic Hazard, and 2721 Wetmore Preliminary Geotechnical Engineering Report Everett, Washington Preliminary Design Recommendations Surface water should be controlled by means of curbs, gutters, or swales, so that water does not flow over exposed soil cuts or newly constructed walls. Drainage behind the shotcrete wall should be provided by installing Mira-Drain or equivalent drainage mats per the manufacturer's recommendations. The drainage mats should be installed behind the shotcrete wall for the full wall height, with the 4-foot-wide fabric strips placed at a spacing of 8 feet on-center for the full length of all walls. The Mira-Drain mats should freely communicate with the perimeter drain system through a series of weep holes or drain sleeves. Care must be exercised when installing soil nails to avoid existing utilities and foundations. Demonstration of utility and foundation protection will be required to obtain a temporary soil nail easement from the City of Everett. 13.2 Soldier Pile Wall One of the most common types of temporary shoring used in the Everett area consists of a soldier pile shoring system. For excavations greater than approximately 15 feet in depth, the soldier beams are laterally restrained with drilled tieback anchors. Soldier piles, which are wide-flange beams, are placed in pre-drilled holes that extend beyond the bottom of the excavation. The portion of each soldier pile extending below the bottom of the excavation is grouted in place with sufficient-strength concrete or CDF to transmit the vertical loads of the soldier beams to the soil below the excavation level. The upper portion of the soldier pile is then backfilled with a relatively weak grout so that it may be removed, as necessary, for placement of lagging. In our opinion, lagging would be required throughout the excavation. We recommend that timber lagging be backfilled with a flowable lean-mix sand during installation to reduce the potential for movement of the cut soil and provide drainage behind the wall. The lagging should span a maximum of 8 feet. A 50-percent reduction of the lateral pressures presented subsequently can be used for timber lagging design to account for soil arching. A temporary cantilever shoring system with up to one row of tiebacks should be designed using the recommended lateral earth pressures illustrated on Figure 3. If adjacent structures, heavy construction traffic, materials stockpiling, or other substantial surcharges are to be applied during construction, these surcharges should also be included in the design. A typical surcharge would be 250 psf at the surface. We recommend a minimum pile embedment depth of 10 feet into the very dense sediments. If more than 6 inches of standing water or slough is present at the bottom of the boring prior to grout placement, the contractor should be prepared to use a tremie pipe to place grout continuously from the bottom up. Grout may consist of lean-mix concrete or CDF, as specified by the structural engineer, to ease chipping for lagging installation. May 28, 2019 ASSOCIATED EARTH SCIENCES,INC. FSM/Id-190168E001-2-Prof ects\201901681KE\WP Page 16 18185B Page 11 of 180