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

SHANNON OWILSON,INC. In approximately the northern 30 feet of the 14th Street bulkhead dredging is proposed to elevation -3 feet at the wall face then sloped down at a 2.5H:1 V slope. At Segment C, approximately Station 8+50, there is an area of proposed dredging about 50 feet in length. Dredging will be performed to elevation -3 feet at the wall face then sloped down at a 2.5H:1 V slope. We performed a slope stability analyses for the dredged area at Segment C and 14th Street Bulkhead. A description of our analyses is included in Section 4.4.2, below. We provided lateral earth pressure recommendations and performed numerical soil-structure interaction (SSI) analyses to support MNE's evaluation of how the dredging will affect the bulkhead. 4.3.1 14th Street Bulkhead We developed lateral earth pressure recommendations for the proposed dredging configuration in front of the existing 14th Street Bulkhead (see Figure 9). We understand that MNE will use this information to perform a structural evaluation of the existing 14th Street bulkhead for the terporary dredged condition. 4.3.2 Segment C We provided lateral earth pressure recommendations for Segment C in Figure 5. We understand that the lateral displacement estimated by MNE based on these lateral earth pressures were too large. The recommendations we provided were based on traditional earth pressure theory, for a single wall configuration. Traditional earth pressure theory cannot account for the double bulkhead configuration that is present in Segment C (upper timber bulkhead behind lower sheet pile bulkhead). Therefore, we performed a two-dimensional (2D) numerical SSI analysis to estimate the deflection of the bulkhead during the temporary dredged condition. The results of this analysis are presented in Appendix D. The SSI analysis was performed using the finite difference software Fast Lagrangian Analysis of Continua (FLAG Ver. 7.0). Continuous materials, such as soil, are modeled by finite difference zones and are assigned a constitutive model appropriate to the stress-strain behavior of the material. Structural components are modeled by elastic, finite element beams and cables that interact with the continuous material zones. Our model consisted of three materials: Fill (Hf/Hfp) from the ground surface to elevation -10 feet, Alluvium (Ha) from elevation -10 feet to elevation -25 feet, and Pre-Vashon Non-glacial Fluvial Deposits (Qpnf)below elevation -25 feet. Geologic history and consistency of these units are discussed in Section 3.2. See Figures D-4 for material parameters, model extents, and boundary conditions. The structural components consist of the sheet pile walls forming the existing bulkhead and two tie rods. The parameters of the 21-1-21761-003-RIfdocx/wp/cIp 2 1-1-?1 761-003 13