3400 RIVERFRONT BLVD Geotech Report 2022-10-25

• • Table 1. Summary of Soil Consolidation Properties • Compression Coefficient of Max Secondary Time to End • • Soil Index OCR2 Consolidation Drainage Compression of Primary Layer Cv Path Index Consolidation 40 Ccar (feetz/day)3 (feet)° Cass (days)6 • Silt and , Organic 0.30 1.0 0.30 7.5 0.010 250 - 300 Silt 40 1. Estimated value based on laboratory tests on similar soil at the nearby Everett Riverfront Simpson site. • 2. Estimated based on site geologic history. 3. Based on site consolidation data from laboratory testing performed by ESNW in March 2015. 4. Estimated based on data from soil borings that indicates the typical thickness of the soft to medium stiff silt and • organic silt layer is 15 feet. Assumes sand drainage layers are present above and below silt layers. 5. Estimated using published correlations for moisture content(Mesri, 1973). • 6. Time required to reach the end of primary consolidation was estimated using values obtained from site consolidation • data. Does not take into account soil surcharge. • We performed a settlement analysis for soil profiles with 10 to 20 feet of soft to medium stiff silt. A We assumed new fill thicknesses of 2 to 10 feet and evaluated both primary and secondary • consolidation settlement. We also evaluated a surcharge program that consists of adding 5-and 10-foot-thick surcharges above final grade and estimated the amount of time required to achieve • approximately 100 percent of primary and 90 percent of secondary consolidation. We assumed a surcharge unit weight of 115 pcf and a 50-year design life in our calculations. • As previously discussed, documented surcharges have previously been placed over most of the • western half of the property. We understand that these surcharges were left in place for at least • two years. Figure 3 shows the locations of the previous surcharges. In our opinion, it is not • necessary to place new surcharge in areas that have previously been surcharged, since the 411 underlying soil has already been sufficiently consolidated. 40 5.2.3 Estimate of Settlement Magnitude and Duration • The amount of consolidation settlement that we estimate will occur in the silt and organic silt • layer from new structural fill is shown in Table 2. Interpolation can be used to obtain settlement estimates for other loading or surcharge scenarios. • • 41 • • • • G EODESIGNY. 8 Polygon-128-01:091615 • •