2023-06-28_ENFORCEMENT - M1982121 ‎(2)‎

• Permit No: M1982121
• IBM Index Class Name: Enforcement
• Doc Date: 6/28/2023
• Doc Name: Rock Failure Analysis and Stability Memo
• From: RMR Aggregates, Inc.
• To: DRMS
• Email Name: ACY
• Email Name: THM
• Media Type: D
• Archive: No

After defining the discontinuity sets, analyses for each mode of potential failure were
performed. The number of the discontinuity stereonet poles that meet the kinematic criteria of
lying within the critical zone for failure are represented on Table 1 as a percentage of the total
number of discontinuities.
Table 1. Summary Results of Kinematic Stability
Analysis for East Face-Critical Failure Poles
Failure Mode Critical Percentage
Poles of Poles
All
4 1.33%
Wedge Intersections
Sets Only 0 0.00%
Limestone 0 0.00%
Planar Slide (Bedding Only)
(No Limits) Mudstone
10 100.00%
(Bedding Only)
Limestone
Planar Slide (Bedding Only) 0 0.00%
(Lateral
Limits) Mudstone 7 70.00%
(Bedding Only)
Note: Failure mode numbers in table represent the percentage of total discontinuity poles that kinematically lie within
the critical zone for failure.
Based on the kinematic analyses, there is a low probability of wedge failure.The results from
the wedge stability analyses indicate a very low probability of failure.
The kinematic analyses corroborate field observations from the field reconnaissance that
indicate the primary failure mode is planar sliding along the limestone bedding planes
consisting of mudstone dipping adversely along the south-facing highwall. Wedge sliding of rock
blocks occurs when the intersection line between two discontinuities plunges in the direction of
the cut face at an angle steeper than the rock friction angle but less steep than the angle of the
cut slopes (Wyllie and Mah, 20044), as seen in Photo 16. Critical intersections represent wedge
geometries that satisfy frictional and kinematic conditions for sliding. This point must fall
outside the cut slope's great circle but within the rock friction kinematic boundary cone to be
considered to have the potential for wedge sliding (red-shaded area in Appendix C figures). The
thin interbed of shaley mudstone observed along some of the limestone bedding planes creates
a potential failure plane of lesser cohesion and fiction angle than the limestone. Stability
modeling was completed to evaluate this geometry for potential failure.
STABILITY MODELING ANALYSIS OF FAILURE MODES
Long Term Steady-State stability analysis along the cut slopes was performed to evaluate the
potential bedrock failures along discontinuities in the rock mass. Results from these analyses
'Wiley, D.C. and C.W. Mah,2004, Rock Slope Engineering,41h Edition,Spoon Press, New York, NY.
Page. 5
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