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Mining Methods and Slope Stability Evaluation for Expanded Development of the Walstrum Aggregate Quarry 2.0 GENERAL SLOPE STABILTY FACTORS AND ISSUES To ensure safe mining operations, the goal of engineers and mine operators must be to design and create slopes that must remain stable for a planned period of time. Failures of rock slopes almost always result from an unfavorable combination of slope height, slope angle, water drainage, seismic accelerations(or excessive blast-induced forces), and geological structure. The basic types of rock-slope failures, shown in Figure 2.1, include: (1) planar block slides, i (2) wedge failures, rotational failure, and (4) toppling. (a) Planer block The accepted industry practice for defining the relative safety of rock slopes is established (b) Wedge failure by determining a factor of safety (FS), which is simply a ratio of the resisting forces R to the driving forces D. Safety and stability ! ,/ occurs when FS > 1. In open pit and quarry mining, slopes are typically designed with (c)Rolotionol failure safety factors at or slightly above one. �r �r Based on the author's observations at the (d)Toppling foiiure Walstrum Quarry, made during several site Figure 2.1 Basic types of rock slope failures. (a) visits over the last 12 years, planar block Planar Block, (b)wedge failure,(c)rotational failures are the most likely mode of slope failure, (d)toppling failure. From SME failure. There is also some chance that MINING ENGINEERING HANDBOOK,p. Rai localized wedge failures could occur in walls where the major foliation planes have unfavorable orientation with joint planes. Theoretical modeling calculations can be used to evaluate the potential for sliding block or planar failures based on slope and block geometry, sliding-plane cohesion, water pressure and seismic loading. In some mines and quarries, the use of theoretical slope stability calculations is impractical due to the complexity and/or quantity of the potential sliding planes. However, in these cases where theoretical approaches aren't practical, the stability of rock slopes can be safely managed by applying other proven methods learned from practical experience. Based on observations of the structural geology in the Walstrum Quarry and experience gained from prior slope failures the author finds that a combination of practical methods offers the best solution for establishing a safe rock slope management program at the Walstrum Quarry. REVEY Associates,Inc. Page 3 of 14 October,2001