2011-09-09_REVISION - M1990057 (3)

Home Browse Search

materials would have slightly differing strength properties. At that time, our direct shear measurements indicated an angle of internal friction which was higher than published data; we used the upper limit of the published data. (continue in item 5) CDRMS question 5. Page 8, Table B: Based on Tables 2.8 and 2.9 in the referenced text by Vick, cyclone tailings could be expected to have a slightly lower friction angle than tailings slimes. Please comment on using the same friction angle for both fine and coarse fractions of tailings. CTL Thompson Response (September 1, 2011 letter) Additional direct shear tests were performed subsequent to our July 6 letter, and were presented in the August 17 letter. The stability analysis results included in the August 17 letter used the measured friction angle (35 degrees) and zero cohesion for the tailings, which is consistent with the range of drained friction angle provided in Vick Table 2.8 for gold slimes. UMC Response UMC has attached the August 17, 2011 letter from CTL Thompson for your review. CDRMS question 6. Appendix B: Stability analyses: a. Figure B -2: Comparing B -2 with B -3, B -2 does not include a layer of cyclone sand that is included in B -3. Please explain why the sand layer was left out of B -2. b. Figure B -5: Comparing B -5 with B -6, B -5 does not include a layer of cyclone sand that is included in B -6. Please explain why the sand layer was left out of B -5. c. Figure B -5: The cohesion used for the tailings in B -5 is 0 psf. However, the cohesion for tailings in B -2 is 50 psf. Please provide an explanation as to why two different cohesions values were used for presumably the same material. CTL Thompson Response (September 1, 2011 letter) 6 -a The configuration of the sand "layer" will be determined by the flow characteristics of the cyclone sand at the time of placement. In our August 17 letter, we used a 3:1 slope for the inside and outside face of the sand. With the same strength parameters used for both the sand and slime, the configuration of the sand has no bearing on computed factors of safety except for the outside slope of the tailings. We believe that the 3:1 outside slope is conservative, since literature suggests a 3:1 to 4:1 slope will actually occur. 6 -b See a. 6 -c See a. (our rationale in the July letter was that the increased fines content in the slime would justify some cohesion. Like Mr. Cazier, we re- thought this assumption when we did our supplemental analysis and eliminated the cohesion). TR3AdequacyReview.Question I9UMCResponse.Sep9.jme.004 M1990 -057 September 9, 2011