1990-01-09_REVISION - M1988112 ‎(6)‎

• Permit No: M1988112
• IBM Index Class Name: Revision
• Doc Date: 1/9/1990
• Doc Name: FAX COVER
• From: STEFFEN ROBERTSON & KIRSTEN
• To: MLRD
• Type & Sequence: AM1
• Media Type: D
• Archive: No

'?6 61 69 16::6• 3 ;5, 98` 59a~ SFK DEI~R
BATTLE MOUNTAIN RESOURCES, 5AN LUIS PROJECT
Ch1L^D ADEQUACY LETTER RFSPDNSFS
Page 10 of 28
Irrespective of the location of the phreatic surface, an evaluation
of tailings liquefaction can be made based on thrr. 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 yratn size distribution should result in a D o size of
approximately 0.25mm or perhaps slightly smaller. Tai~ings sands
which are located slightly further from the spigotinq points than
the "beach" sand is assumed to have a DS size of approximately
0.15mm (No. 100 sieve) and a void ratio of a.7 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.
'Rork conducted by Seed and [driss (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 ar•e presented on Figure i).6-16 and as
in the: following discussion:
No liquefaction of beach sands will occur for a road ratio of
0.8 if the seismic induced acceleration is less ttan IS percent
of yravlty for a minimum of 15 cycles (site pe,~k ground
acceleration of .23g resulting from a Magnitude 7.5 e4rtnquake
approximately 28 miles away). No liquefaction of beach sands
at a void ratio of 0.1 can occur if the seismic induced
acceleration is less than .25g for 15 cycles;
No liquefaction of sands slightly further from >pigot points
will occur if seismic induced acceleration is ~ess than .2g
for 15 cycles; and
No liquefaction of tails some distance from the beach if the
seismic induced acceleration is less than .2g and no
liquefaction dt all if the void ratio is less t~nan 0.8 under
all but very ex:re.ne accelerations.
From the analyses presented in the above discussions it does not
appaar that liquefaction of the tailings immediately below the Phase
2 raises is likely to acc;:r. 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.
!t should be noted that in the event that the tailings materials are
not suitable for construction of the upstream raise'„ sufficient
space has beers allowed downstream of the main "starter" embankment
for constructiu~~ of centerline or downstream raises.
63