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

American Property Develo!,..'ent ES-0599.05 January 16, 2015 Page 11 Updated January 22, 2015 With structural loading as expected, total settlement in the range of one inch is anticipated, with differential settlement of about one-half inch or less over the span of a typical column spacing. The majority of the settlements should occur during construction, as dead loads are applied. Slab-On-Grade Floors Slab-on-grade floors for the proposed building structure should be supported on competent native soil or a compacted structural fill subgrade, as appropriate. Unstable or yielding areas of the subgrade should be recompacted or overexcavated and replaced with suitable structural fill prior to construction of the slab. A capillary break consisting of a minimum of four inches of free draining crushed rock or gravel should be placed below the slab. The free draining material should have a fines content of five percent or less (percent passing the #200 sieve, based on the minus three-quarter inch fraction). In areas where slab moisture is undesirable, installation of a vapor barrier below the slab should be considered. Retaining Walls Retaining walls should be designed to resist earth pressures and any applicable surcharge loads. For design of the garage level foundation walls, the previous earth pressure values provided for cantilever and multiple tieback shoring walls should be used, as appropriate for yielding and restrained wall conditions. These earth pressure values were previously provided in the Shoring Recommendations section of this study. With respect to site retaining walls constructed independent of the building foundation walls at or near existing site grades, the following values should be used for design: Site Retaining Walls • Active Earth Pressure (Yielding Wall) 35 pcf(equivalent fluid / granular fill) • At-Rest Earth Pressure (Restrained Wall) 50 pcf • Traffic Surcharge (Passenger Vehicles) 70 psf (rectangular distribution) • Passive Resistance 350 pcf (equivalent fluid) • Allowable Soil Bearing Capacity 4,000 psf (preliminary) • Coefficient of Friction 0.40 Additional surcharge loading from foundations, sloped backfill, or other loading should be included in the retaining wall design, as appropriate. Drainage should be provided behind retaining walls such that hydrostatic pressures do not develop. If drainage is not provided, hydrostatic pressures should be included in the wall design, as appropriate. The geotechnical engineer should review retaining wall designs to verify that appropriate earth pressure values have been incorporated into the design and to provide additional recommendations, as necessary. Earth Solutions NW,LLC