REP34115

• Permit No: M1988112
• IBM Index Class Name: Report
• Doc Date: 7/14/1995
• Doc Name: SAN LUIS MINE PHASE II RAISE 2 DESIGN REPORT VOLUME I OF II
• Media Type: D
• Archive: No

' San Luis Mine Phase Q, Raise 2 Design Reporc
' Samples of tailings slimes submitted for Atterburg Limit determination resulted in liquid limits of
20.0 to 24.2 and no plastic limits (i.e. non-plastic). The results of the Atterberg Limit
determinations are presented in Appendix D.
A composite sample of silty tailings sand was subjected to a 3-point consolidated-undrained triaxial
' shear strength test. Test specimens consisted of re-molded tailings samples which were placed in
the triaxial cell, saturated and then consolidated under loads of 15, 28, and 54 psi which is roughly
equivalent to 18, 34 and 65 feet of tailings, respectively. Shearing was conducted under undrained
conditions with pore pressure measurements recorded. In terms of effective stresses, the Mohr-
Coloumb shear strength parameters at 5 percent strain are a friction angle of 34 degrees and no
' cohesion. At peak stress, the friction angle is slightly higher at 34.5 degrees. These test results
are included in Appendix D.
In terms of undrained (total stress} shear strength, the tailings sand exhibited a friction angle of
23.4 degrees and no cohesion at 5 percent strain. This material exhibited a total stress friction angle
' of 26.7 degrees and no cohesion at peak shear strength. These test results are also included in
Appendix D.
' The tailings sand specimens consolidated at confining pressures of 15 and 54 psi exhibited dilatent
behavior and strain hardening effects at shear strains up to 15 percent. At the 28 psi confining
_ pressure the material exhibited contractive behavior with a residual shear strength on the order of
' 1900 psf at an axial strain of approximately 8 percent. The 28 psi load increment was actually the
third data point in the test and the test specimen consisted of a sample which was remolded from
' the samples prepared for the previous data points due to a shortage of material. Multiple remoldings
and shearing may have caused fracture of the grains at contact points thereby resulting in somewhat
' rounder grains, contractive behavior and less reliable results.
A sample of tailings slimes was subjected to a 3-point consolidated-undrained triaxial shear strength
' test in conjunction with the design studies performed for Raise 1. Test specimens consisted of re-
molded tailings samples which were placed in the triaxial cell at approximately 80 pcf, saturated and
then consolidated under loads of 20, 45 and 75 psi. Shearing was conducted under undrained
conditions with pore pressure measurements recorded. All specimens exhibited dilatent behavior
and strain hardening effects at shear strains up to 20 percent. In terms of effective stresses, the
' Mohr-Coloumb shear strength parameters at 5 percent strain are a friction angle of 30.6 degrees and
331 psf cohesion. For a strain of 10 percent, the strength is slightly higher with a friction angle of
31.8 degrees and 562 psf cohesion. At peak strength, [his material exhibited a lower effective
friction angle of 28.4 degrees and a higher cohesion of 835 psf. These test results are included in
Appendix D.
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