2015-04-13_REVISION - M1974086 ‎(6)‎

• Permit No: M1974086
• IBM Index Class Name: REVISION
• Doc Date: 4/13/2015
• Doc Name: Adequacy Response No. 2
• From: Greg Lewicki and Associates, PLLC
• To: DRMS
• Type & Sequence: AM3
• Email Name: MAC
• Media Type: D
• Archive: No

Asphalt Paving Co.
Geotechnical Stability Evaluation
April 2, 2015
Page 3of4
Eight slope configurations were analyzed in total: four strikes corresponding to South, West,
East, and North dip directions with each strike being analyzed for the double bench and overall
slope cases.
The results of the analyses are presented in the table below.
Analysis
Slope Dip
Direction
(deg)
Slope Dip
Angle
(deg)
Analysis Height
(ft) )
Lowest
Calculated
Wedge FOS
West Dipping Overall
251
90
200
1.37
West Dipping Bench
251
90
80
2.89
South Dipping Overall
180
79
400
1.35
South Dipping Bench
180
90
80
2.33
East Dipping Overall
120
73
400
1.35
East Dipping Bench
120
90
80
1.32
North Dipping Overall
0
86
200
1.38
North Dipping Bench
0
90
80
2.27
The width of this wedge failure was restricted to mimic practical distance between repeating near -
vertical joint sets observed in the field.
The outputs from Swedge are presented in Appendix A. Wedges for the general analyses were
limited to a persistence of 500 ft along any given joint. Limiting the persistence or "scaling" of
the wedge in this manner results in more realistic wedges being calculated by the program as
any particular joint is not likely to be continuous and connected throughout the rock mass.
Brierley elected to limit the allowable width of the wedge failure to a practical joint spacing of
approximately 90 ft, which is a more conservative distance than generally observed in the field.
Utilizing this reasonable restriction, a FOS of 1.3 or higher resulted.
1.4 Conclusion
As previously noted, the observations of the contact between the altered shale and the basalt
indicate no stability issues at the contact. Additionally, limit equilibrium modeling of the thin
basalt veneer over the shale results in acceptable FOS. The slope angle of the east - dipping
slope may be controlled by the presence of the contact, and the mine's best interests to avoid
the shale. Therefore, the proposed final east - dipping slopes will be dictated by the slope dip
angles in the table above or avoidance of the shale, whichever is flatter.
Within the basalt, a few localized slides along dip -slope joint orientations are present within the
existing quarry benches, generally where east -west trending vertical joints act as the sidewall
for the dip -slope surfaces. However, the majority of exposed benches with similar aspect and
geometries are stable. Occasional slides of similar scale may occur during future mining
operations due to slight variations in the site geology which is not representative of the overall
BRIERLEY
ASSOCIATES
Creating Space Underground