3214 BROADWAY SEPA 017 - 004 Geotech Report 2025-04-14

American Property Development ES-0599.05 January 16, 2015 Page 9 Updated January 22, 2015 Timber Lagging Lagging should be installed in maximum four foot lifts as the excavation is advanced. Lifts of up to six feet maximum may be acceptable for short periods, provided the lagging is installed immediately. The geotechnical engineer should observe the shoring excavation to assess the stability of the cut. The lagging should be backfilled as the excavation is advanced to minimize voids between the lagging and cut face, and to reduce the potential for ground subsidence behind the shoring wall. Where sloughing of the excavation results in the development of a large void, injecting lean mix into the void area should be considered. Due to anticipated soil arching between soldier piles, the timber lagging can be designed with a reduced pressure equal to thirty five percent of the design lateral earth pressure. Tieback Anchors Tiebacks should be located as high on the wall as possible and should be designed based on the following parameters: • Allowable Anchor Friction 1,900 psf • Declination Angle 15 to 20 degrees (from horizontal) • Soldier Pile End Bearing 18,000 psf • No Load Zone See Plate 5 of this study Tieback anchors should be verification tested and proof tested in general accordance with Section 8.3 of the Recommendations for Prestressed Rock and Soil Anchors (Post-Tensioning Institute, 1996). A minimum of two verification tests (200 percent design load) should be performed. Verification test anchors can be used as production anchors, provided the anchor is successfully tested and is acceptable. The production anchors should be proof tested to one hundred thirty percent of the design load. The geotechnical engineer should observe the anchor testing and provide documentation of the test results. Tieback anchors should be locked-off at ninety percent to one hundred percent of the design load. Shoring Wall Drainage Temporary shoring walls should be provided with adequate drainage to reduce the potential for excess hydrostatic pressure build-up. During construction, drainage occurring between the timber lagging is usually sufficient to prevent the development of excessive hydrostatic pressures. Where permanent building walls will be constructed along the temporary shoring walls, a sheet drain material should be installed along the face of the shoring wall. A typical detail illustrating a sheet drain and permanent wall drainage system is provided on Plate 6 of this study. Earth Solutions NW, LLC