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Photogrammetric mapping for pit slope angle optimisation

SRK News | Issue 54: Rock Engineering and Slope Stability

A4   |   Letter

The requirement to optimise excavation design and minimise waste stripping is becoming more critical in pit engineering as pits deepen and economics become tighter. Representative structural data is critical when optimising pit slope angles and in most circumstances, the access for mapping the required data is restricted due to Health and Safety concerns accompanied by time constraints.

Photogrammetry mapping is a remote data capture system that uses digital photogrammetry to produce accurate 3D structural models of mine features. Using photogrammetry mapping software, three dimensional photogrammetric images of rock faces can be produced rapidly and safely while remaining cost effective. The 3D images are then mapped using specialist computer software, producing rock mass measurements, which can subsequently be used for a variety of geomechanical applications.

SRK has successfully used photogrammetry mapping to collect rock mass data from a mine in the Amur region of Russia, which has been used to optimise pit slope angles with significant cost benefits for their clients.

The photogrammetric mapping is carried out on both the hangingwall and footwall. Overlapping 3D images are stitched together to form mosaics that allow mapping of larger (full bench and multi-bench scale) features that span across numerous models. Over 4,000 data points were mapped over 8 hours from the photogrammetric models. The photogrammetry mapping data was used to characterise the rock mass and carry out a stability analysis, assessing the effect of increasing slope angles for the bench stability and for the overall slope.

SRK was able to recommend an increase in the current pit slope angle configurations: the inter ramp angle was increased to 59° from 55° and the bench angle was increased to 75° from 65° allowing for a bench height of 30m and berm width of 10m. The increase in inter ramp angles reduced the amount of waste material that the client needed to remove before reaching ore. An increase of 2° over a 250m high pit saved approximately 10% in waste stripping costs when compared to the original design.

Karl Llewelyn:

SRK Africa