REP16163

• Permit No: M1988112
• IBM Index Class Name: Report
• Doc Date: 7/14/1993
• Doc Name: SAN LUIS MINE PHASE II RAISE 1 DESIGN REPORT
• Media Type: D
• Archive: No

L
' San Luia Mine - Phsae n, Race I Deaig~ Report
At each abutment, the raise will underlain by VLDPE geomembrane liner anti a drainage layer as
described in the Amendment. The VLDPE liner will be welded to the existing liner to form a
' continuously lined facility.
' 4,0 STABILITY ANALYSES
' 4.1 Liquefaction Triggering
As the bulk of the tailings which will underlie the embankment raise are non-saturated, as
' demonstrated by the CPT probes, no liquefaction of these tailings can occur as a result of an
earthquake. The tailings currently at a depth of approximately 15 to 18 ft (elev 8555-8552) may
be saturated and therefore susceptible to earthquake induced liquefaction.
' The liquefaction triggering procedures presented by Seed and Idriss (1982) and the U.S. Bureau of
' Reclamation (1989) have been used to evaluate the liquefaction potential of than layer. Following
these procedures, this layer could be anticipated to liquefy during a magnitude 6.0, 7.0 and 7.5
earthquake producing peak ground accelerations at the tailings dam site of approximately 20, 22.3
' and 26.2 percent of gravity, respectively.
' The liquefaction triggering calculations are presented in Appendix C.
4.2 Material Properties
' Consistent with the Amendment, the embankment fill has been conservatively modeled as a
cohesionless fill with a friction angle of 35°. For potential failure surfaces of tha downstream slope
which may involve sliding along the VLDPE liner, the liner has been modeled as a 0.5 ft thick layer
with a friction angle of 18° and no cohesion. Review of technical literature on the subject and the
results of direct shear testing of granular soil to VLDPE liner interface for other projects reveal that
a friction angle of 18° is very conservative for VLDPE liner. A friction angle of 25 ° is typical for
this type of liner. Nevertheless, for lack of specific test data, a friction angle of 18° was utilized
to maintain consistency with previous design analyses.
' The vast majority of the tailings which will underlie the raise are non-saturated as demonstrated by
the CPT probes. Therefore, no liquefaction can occur under seismic loading and the undrained
shear strength of the tailings will govern its behavior under loads produced by the overlying dam
raise. Consistent with the triaxial shear test data, the bulk of the tailings have been modeled with
' July 13, 1993 5 SRK 1''toject No. 14719