Question 7 of 27

Question 1.7 (5 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

1.7.1 — why monitor even after good design. Slope DESIGN uses average, sampled rock-mass properties (RMR/Q, joint sets, strength) that can never fully capture every local structural anomaly, blast-damage zone, or pore-pressure change encountered as mining actually advances; groundwater, blast vibration, and progressive stress redistribution as the pit deepens all continue to change conditions AFTER design is finalised. Displacement monitoring (prisms, radar, InSAR, extensometers) is the only way to detect the onset of movement in real time, giving early warning of a developing failure BEFORE it becomes catastrophic — design reduces the probability of failure, monitoring manages the consequence of a failure the design could not fully anticipate.

1.7.2 — Bieniawski. Z.T. Bieniawski developed the Rock Mass Rating (RMR) system (1970s–80s), a practical empirical classification combining intact rock strength, RQD, discontinuity spacing/condition, and groundwater into a single 0–100 score used worldwide to guide slope angle, support design and excavation method selection. Achievements: simple, field-repeatable, requires no advanced numerical modelling, and correlates reasonably well with rock-mass deformation modulus and stand-up time, making it hugely influential across mining and civil rock engineering. Shortcomings: RMR is empirical, not mechanistic — it does not directly model the actual failure mechanism, can be subjective between raters classifying the same face, and was calibrated primarily on TUNNELLING case histories, so its direct application to open-pit slope stability (very different stress path and much larger scale) requires caution and is usually supplemented by kinematic and limit-equilibrium analysis rather than used alone.