Question 5 of 13: Hydraulic Mining and Wall-Slope Monitoring

Question 1.5: Hydraulic Mining and Wall-Slope Monitoring (6 marks, compulsory)

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.

1.5.1 – Minerals mined by hydraulic monitor. Hydraulic monitoring (high-pressure water jets breaking down and transporting unconsolidated or weakly consolidated material) is classically used for: placer gold, cassiterite (placer tin), phosphate rock, and kaolin (china clay) – all commodities that occur in soft, poorly cemented deposits amenable to being broken and slurried by a water jet rather than requiring drill-and-blast.

1.5.2 – Why monitoring remains essential after design. A rock-mechanics slope design is built from a FINITE sample of structural mapping, joint-orientation surveys, and geotechnical drilling – it cannot capture every discontinuity in the rock mass, particularly low-frequency but high-consequence structures (a single unmapped fault or bedding-plane weakness) that lie between sampled sections. Groundwater/pore-pressure conditions, and the disturbance blasting itself introduces to the wall, also evolve continuously as the pit deepens in ways the original design can only estimate. Displacement monitoring (survey prisms, radar, extensometers) tracks the WALL'S ACTUAL behaviour in real time, giving early warning of progressive deformation (accelerating displacement trend) that signals an incipient failure the design's calculated factor of safety cannot, by itself, guarantee will not occur – it is the operational check on a design built from necessarily incomplete data, not a redundant formality.