2009-10-16_PERMIT FILE - M2009082 ‎(27)‎

• Permit No: M2009082
• IBM Index Class Name: PERMIT FILE
• Doc Date: 10/16/2009
• Doc Name: Stability Analysis
• From: Lafarge West, Inc.
• To: DRMS
• Media Type: D
• Archive: No

DRMS Analysis, Highwall Setback to Property Line
The Division of Reclamation Mining and Safety (DRMS) requires that gravel pit highwalls within 200
feet of significant manmade permanent structures (such as utilities) be investigated for slope stability.
Furthermore, the DRMS requires that the gravel mine highwalls be modeled as vertical unless it can be
demonstrated that the slope angle of the highwall will be controlled during mining. Additionally, the
DRMS requires that the analysis be performed using the DRMS parameters for sites where laboratory
testing is absent. These parameters are given below on Table 2:
Table 2: DRMS Model Parameters

Soil Type Effective
Friction Angle
(de rees) Effective
Cohesion
c' (psl) Saturated Unit
Weight
sir ( c
Overburden 28 50 114
Gravel 35 0 130
Weathered Bedrock 14 0 124
Bedrock 28 100 124
The parameters for weathered bedrock are much more conservative than those typically encountered in
the project area and, it is our opinion, that they are not representative of conditions at the site.
We analyzed a vertical highwall section for each phase. The depth to bedrock varied from 7 to 31 feet
across the project site. The vertical section corresponds to a steep highwall mining scenario where the
highwall inclination is approximately 0.5:1.
Table 3 below summarizes the results of our analysis. The analysis was performed using the DRMS
parameters shown in Table 2. The factor of safety required by the DRMS for temporary mine slopes
and reservoir embankments are provided for comparison. Output graphics for each of the analyses are
attached.
Table 3: Hi2hwall Setback DRMS Analvsis Resultc

Model Setback
Distance (feet) Calculated
Facto

er of
Saf Required Factor

of Safety
Phase IA 46 1.00 1.0
Phase 1B 39 1.01 1.0
Phase 1C 30 1.04 1.0
Phase 2 Eastside 35 1.03 1.0
Phase 2 Westside 37 1.03 1.0
Phase 3 25 1.11 1.0
Phase 4A 25 1.10 1.0
Phase 4B 25 1.11 1.0
Phase 4C 25 1.16 1.0
Phase 5A 25 1.21 1.0
Phase 5B 25 1.08 1.0
Phase 5C 25 1.25 1.0
Longterm Case 25 1.68 N/A
The setback distance in Table 2 is calculated from the crest of the mine highwall to the potential failure
surface intersection with the existing ground.
Parsons Mine
DRMS 112 Permit
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