1018 14TH ST 2023-02-09 - Laserfiche WebLink

SHANNON MMILSON,INC. 4.4 Slope Stability We performed slope stability analyses to evaluate minimum pile penetration depths for the new bulkhead. We also performed analyses to evaluate temporary dredging configurations. The slope stability analyses were performed using the limit-equilibrium stability program SLOPE/W, Version 7.21, by Geo-Slope International for various bulkhead and slope conditions. We used the Morgenstern-Price method, which satisfies both force and moment equilibrium,to calculate a FS for various failure surfaces extending globally, around the proposed bulkhead configuration. The SLOPE/W program performs a search for the critical failure surface (representing the lowest FS) based on established starting and ending points. We performed the analyses to check that minimum FS criteria of 1.5 for static loading conditions and 1.1 for seismic loading conditions were met for the permanent bulkhead configurations. For temporary dredged conditions, an FS of LI to 1.3 was considered for acceptable for static loading conditions (no seismic analyses). These criteria are based on recommendations by the Washington State Department of Transportation (WSDOT), see Chapter 7.4 of the WSDOT Geotechnical Design Manual (2013). 4.4.1 Bulkhead Configurations We performed an analysis of a representative cross section for Segments A. B, and C under the permanent bulkhead configuration. The geometry of the permanent bulkhead at Segments A, B, and C were based on information provided by MNE. The results of the analyses are shown in Figure 10 and indicate that global stability criteria were met for the conditions analyzed. 4.4.2 Segment C and 14"' Street Bulkhead Temporary Dredged Condition We performed analyses for temporary dredging in front of the bulkheads at Segment C (see Figure 1 1) and 14`h Street (see Figure 12)assuming dredging would be to elevation -12 feet. The analyses results indicate that the global stability criterion was met. Based on communications with MNE in January 2014, we understand that the proposed dredging configuration has changed since the analyses were performed. Currently, proposed dredging will be limited to elevation -3 feet at the toe of the bulkhead and will slope down at 2.5H:1 V to about elevation -12 feet. This configuration will provide increased global stability over the conditions presented in Figures 11 and 12. 21-1-21761-003-air.aacx✓Wpic1p 21-1-21761-003 15