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A.� <br /> Mr. Brandon Guite <br /> Henderson Mill <br /> March 29, 2018 <br /> Page 4 <br /> release of tailings or process water. In addition,the strain levels and development of stresses <br /> in the model does not show any potential for progressive failure which would lead to <br /> cracking or piping, and the embankment movement is stabilized after shaking(as evidenced <br /> by the displacement time histories in figures 24 to 29 within the report,which show that the <br /> movement has stopped). Tolerable deformation does not mean that there is not some level of <br /> maintenance and repair that would be needed on the facility after such an extreme event <br /> (10,000 year event). <br /> We would also like to clarify that the 4.5 ft of displacement is a vector magnitude <br /> displacement observed for Stage 4. The maximum crest settlement(Z direction) at Stage 4 is <br /> less than 2 ft and maximum crest horizontal movements (X direction) is less than 2.2 ft(as <br /> shown in figures 27 and 28 within the report). In addition,the seismic displacements would <br /> be expected to decrease due to drainage after deposition ceases,as discussed under Comment <br /> 3. <br /> However,this TR is seeking an approval for the first stage of construction which has less <br /> than 1.2 ft of settlement(Z direction) and less than 1.8 ft of horizontal movements(X <br /> direction)at the crest(as shown in figure 21 and 22 within the report). This meets tolerable <br /> deformation as defined above. Maintenance and repair would still be needed on the facility <br /> after the extreme earthquake event. <br /> Similar to other comments,the conclusions of the deformation analyses, and what level of <br /> displacement can be considered tolerable, have also been reviewed and confirmed by the <br /> third party TRB mentioned earlier. <br /> DRMS Comment 5 <br /> In the Results section of the AECOM report dated January 26, 2018, the Engineer states <br /> the contours indicate the failure mechanism engages the majority of the downstream slope, <br /> extending from the dam crest to the toe of stepback and original dam, and nearly to the left <br /> and right abutment contacts. Earlier is the report, the Engineer indirectly acknowledged <br /> the potential for transverse cracking due to differential movement near the embankment <br /> abutments, which was the Engineer's reasoning for the 3D analysis. <br /> The 3D model results, Figures 20 and 26, appear to show a relatively rapid longitudinal <br /> transition from large displacement to very little displacement near the natural knob in the <br /> middle of 3-Dam. Please explain whether transverse cracking leading to internal erosion <br /> could occur in this location. If so,please explain what measures are required to prevent <br /> erosion at the location. <br /> M1DCSIPROJECTSIWTR160551494 HENS SUTTR1500-DELIVERABLESIORMS REPORTORMS COMMENTSONALOWS RESPONSE_AECOM_FINAL DOCX <br />