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A=COM Henderson 3 Dam Buttress Design January 26, 2018 Page 10 4. Poisson's ratio 5. Shear modulus and damping variations with strain Table 2 summarizes the material properties used in the deformation analyses in addition to the shear strength properties used in the stability analyses. Results The 3D deformation analysis was performed on 3 Dam with Stage 1 and 4 (final stage) buttresses and crest elevation of 8,883 feet and 8,900 feet respectively. For Stage 1 with crest elevation of 8,883 feet, the calculated displacements for the dam crest with final stage buttress using the selected median 10,000 -year earthquake time history is less than 3.5 feet with the maximum crest settlement of 1.5 feet and horizontal upstream (US)/ downstream (DS) crest displacement of less than 2.0 feet. The surface expression of the critical failure surface is illustrated with contours of shear strain increment at failure on Figures 18 and 19. The contours indicate that the failure mechanism engages the majority of the downstream slope, extending from the dam crest to the toe of stepback and original dam, and nearly to the left and right abutment contacts. Contour of displacement at the end of analysis is shown in Figure 20. Figure 21 and 22 provide the nodal time histories across the dam crest. As shown in these figures, the movement arrest and comes to equilibrium after motion. Exaggerated deformed mesh is depicted on Figure 23. For Stage 4 with crest elevation of 8,900 feet, the calculated displacements for the dam crest with final stage buttress using the selected median 10,000 -year earthquake time history is less than 4.5 feet with the maximum crest settlement of 2 feet and horizontal USMS crest displacement of less than 2.5 feet. The surface expression of the critical failure surface is illustrated with contours of shear strain increment at failure on Figures 24 and 25. The contours indicate that the failure mechanism engages the majority of the downstream slope, extending from the dam crest to the toe of stepback and original dam, and nearly to the left and right abutment contacts. Contour of displacement at the end of analysis is shown in Figure 26. Figure 27 and 28 provide the nodal time histories across the dam crest. As shown in these figures, the movement arrest and comes to equilibrium after motion. Exaggerated deformed mesh of 3 Dam with Stage 4 buttress is depicted on Figure 29. Filter Design The buttress also contains a chimney drain and blanket drain to collect seepage at the interface of the buttress and the current step back and original dam, as shown on the design drawings. The drain design intent is to provide seepage management. The thickness is based on construction criteria, which will exceed seepage capacity requirements. It is expected that the seepage will infiltrate back into the existing dam shell further away. Therefore, a toe ditch is not included in the design. The filter consists of a 1.5 feet ASTM C33 sand or similar material. Filter compatibility analysis was performed to develop the gradation of the filter materials using the NRCS filter compatibility criteria and Foster and Fell (2001) erosion control as shown on Figure 30. Filter compatibility is based on the gradation of fine-grain tailings sand encountered at the toe of 3 Dam. The filter compatibility was performed based on using the tailings sand material for the buttress. To follow good practice, a limitation to the rate of rise during construction will be applied to limit pore pressures from rising too quickly. Generally, pre -construction pore pressure values will return within months of each stage of construction completion. During construction, pore pressure measurements will be reviewed to monitor that the pore pressure ratio (change in pore pressures over the change in total applied stress) does not approach 1 during construction. MC CVPW*ftlri1 WO511K-HBt]-Mft11' W4D* r �TRM8 R"-WtWW?MwWwtwl 3 Gun &Ml Gam L.K. R wLft. 6 R.Ld=