1998-01-10_REVISION - M1988112

• Permit No: M1988112
• IBM Index Class Name: Revision
• Doc Date: 1/10/1998
• Doc Name: SAN LUIS PROJECT PERMIT AMENDMENT ADEQUACY RESPONSES M-88-112
• From: STEFFEN ROBERTSON & KIRSTEN
• To: MLRD
• Type & Sequence: AM1
• Media Type: D
• Archive: No

1

BATTLE MOUNTAIN RESOURCES, SAN LUIS PROJECT
CMLRD ADEQUACY LETTER RESPONSES
Page 10 of 28
Irrespective of the location of the phreatic surface, an evaluation
of tailings liquefaction can be made based on the grain size
distributions and anticipated void ratios. Processing of the ore will
produce tailings with 100 percent passing a No. 50 sieve (0.3mm).
For the beach sands the void ratio is conservatively estimated to
be 0.7 to 0.8 after consolidation (based on laboratory testing) and
the grain size distribution should result in a D o size of
approximately 0.25mm or perhaps slightly smaller. Ta~ihings sands
which are located slightly further from the spigoting points than
the "beach" sand is assumed to have a Ds size of approximately
0.15mm (No. 100 sieve) and avoid ratio of a.1 to 0.8. Even further
from the spigots the tails can be assumed to be a fine sandy silt
with a void ratio of 0.75 to 0.85.
Work conducted by Seed and Idriss (1982), based on actual field
performance of sites with a potential for liquefaction, was employed
to evaluate the liquefaction potential of the tailings with
characteristics as presented above (assuming 100 percent saturation).
The results of this analysis are presented on Figure D.6-16 and as
in the following discussion:
• No liquefaction of beach sands will occur fora vnid ratio of
0.8 if the seismic induced acceleration is less than 15 percent
of gravity for a minimum of 15 cycles (site peak ground
acceleration of .23g resulting from a Magnitude 7.5 earthquake
approximately 28 miles away). No liquefaction of beach sands
1 at a void ratio of 0.7 can occur if the seismic induced
acceleration is less than .25g for 15 cycles;
' No liquefaction of sands slightly further from spigot points
will occur if seismic induced acceleration is less than .2g
for 15 cycles; and
1
No liquefaction of tails some distance from the beach if the
seismic induced acceleration is less than .2g and no
liquefaction at all if the void ratio is less than 0.8 under
all but very extreme accelerations.
From the analyses presented in the above discussions 'it does not
appear that liquefaction of the tailings immediately below the Phase
2 raises is likely to occur. Prior to construction of the raises the
actual tailings characteristics will be determined by in-situ testing
of the tailings and laboratory testing to assess their suitability
for supporting the Phase 2 upstream raises.
It should be noted that in the event that the tailings materials are
not suitable for construction of the upstream raises, sufficient
space has been allowed downstream of the main "starter" embankment
for construction of centerline or downstream raises.