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SHANNON€WILSON,INC. <br /> structural elements are included in Figure D-4; locations of the structural elements are shown in <br /> Figured D-5. <br /> Our analysis included the following general steps: <br /> I. Build the model under existing conditions. We used a Mohr-Coulomb constitutive <br /> model for the soil. Soil parameters for our model are based on the results of the <br /> borings, index laboratory tests, and our experience with similar soils. <br /> 2. Solve the model under gravity. The step is necessary to approximate the initial <br /> internal soil stress conditions and evaluate the earth pressures on the lower and upper <br /> bulkhead for the existing condition. The internal stresses and earth pressures depend <br /> on the sequence of construction of the two bulkheads. Based on discussions with the <br /> Port of Everett, we modeled the construction sequence assuming that the two existing <br /> bulkheads and deadman anchor were constructed simultaneously and then backfilled. <br /> This process results in wall deflection. <br /> 3. Incrementally remove the soil in front of the lower bulkhead to simulate excavation <br /> and solve the model. <br /> Based on discussion with NINE, we performed three analyses for different dredge <br /> configurations, as shown in Figures D-1 through D-3 in Appendix D. These analyses included <br /> variation of the current elevation of the mudline at the wall face and variation of the slope of the <br /> rnudline during dredging. The use of a temporary pile with a tieback in front of the existing <br /> bulkhead was also evaluated in these analyses. The analyses results are presented in <br /> Figures D-1 through Figure D-3 and include maximum lateral sheet pile displacement, sheet pile <br /> shear force, sheet pile moment, axial load, and anchor axial load. The results are presented in <br /> 1-foot excavation intervals. <br /> Based on the SSI analyses and discussions with VINE, we recommend that the mudline <br /> elevation during dredging at Segment C be no lower than elevation -3 feet at the face of the wall <br /> and that the slope of dredging be no steeper than 2.5H:1 V. In our opinion, this approach would <br /> allow for performing the proposed dredging without the need for additional temporary shoring. <br /> Our analyses indicate that bulkhead deflections for this condition would generally be less than <br /> about 1 inch. To further increase stability during dredging and reduce bulkhead deflections,we <br /> recommend that the dredging be performed in small sections (10 to 20 feet wide), where <br /> possible, and filled in prior to moving to the next section. <br /> 21-1-21761-003-RI f docx4p/cIp 21-1-21761-003 <br /> 14 <br />