3400 RIVERFRONT BLVD Geotech Report 2022-10-25

• • • • Table 2. Summary of Settlement Results for New Fill • Duration of Surcharge to I Predicted Achieve 100 Percent of II Silt Height of Consolidation Settlement Primary and 90 Percent of • Thickness New Fill (inches)' Secondary Consolidation (feet) (feet) (days) • Primary Secondary Total 5 Foot 10 Foot Surcharge Surcharge • 10 2 _ 1.8 2.2 4.0 80 30 40 15 2 2.5 3.4 5.9 90 40 • 20 2 3.2 4.5 7.7 100 40 • 10 10 7.4 2.2 9.6 200 100 15 10 10.6 3.4 14.0 220 100 • • 20 10 13.5 4.5 18.0 240 100 • 1. Range of predicted consolidation settlement values is based on 2 to 10 feet of fill being placed at the site to raise grades to finish elevations. • • 5.2.4 Settlement of Existing Utilities • Most of the existing utilities at the site are located west of the existing Eclipse Mill Road beneath the drainage swale. The 48-inch sewer line is at the bottom of the swale and the 72-inch sewer line is near the top of the swale adjacent to the existing gravel road. According to a previous report prepared for the site (URS, 2009), the 72-inch pipeline is supported on piles across most • of the site. A water line and telemetry line are located between the two sewer lines. The water • line and telemetry line will be replaced as part of this project. All of these utilities will be beneath the new roadway built for this project that will span the drainage swale and part of the existing • Eclipse Mill Road. • There are two storm drain lines that cross the drainage swale on the north side of the site. One of the storm drain lines will be abandoned as part of this project and the other one (a 42-inch • pipe)will remain. A section of the remaining 42-inch-diameter storm drain line will be located • beneath a future roadway(Road B). • • In anticipation of future development at the site, the City commissioned URS to evaluate the impact that development would have on the existing utilities beneath the site (URS, 2009). The • City provided URS with the anticipated final grades to use in the analyses. URS then provided • estimates of settlement, evaluations of the pipeline strengths, and recommendations for • mitigation. We understand that the City has provided recommendations to Polygon on the final • roadway elevations that should be used to avoid damaging their underlying utilities. • 5.3 SEISMIC HAZARDS • 5.3.1 Liquefaction Susceptibility • Liquefaction is a phenomenon caused by a rapid increase in pore water pressure that reduces the effective stress between soil particles to near zero. The excessive buildup of pore water pressure • results in the sudden loss of shear strength in a soil. Granular soil, which relies on interparticle II IA • G EO DESIGN= 9 Polygon-128-01:09161 5 •