Geotech

Exxaro Resources is developing a new bord and pillar underground mine at its Dorstfontein Coal Mine East (DCME), 10 km north-east of the town of Kriel in Mpumalanga. The new underground mine will be accessed via seven portals driven from the base of the existing Pit 2 open cast operation. In order to ensure the safe operation of the new underground mine, the existing Pit 2 highwall was redesigned to a slope geometry appropriate to the projected 20-year life of the new underground mine. The collaborative services of Rockland Geoscience and ARQ Geotech were retained to design the highwall and monitor blasting and excavation works.

 An in-depth geotechnical investigation was undertaken to determine the geological profile and the condition of the insitu material that will be exposed in the face of the new highwall. The investigation included a desktop study of all available information (including geological maps), 3D terrestrial laser scanning, geotechnical drilling, down-hole surveys, borehole sample logging, laboratory testing and surface mapping.

The data/results obtained from the geotechnical investigation was utilised to inform the slope stability design conducted for the new highwall. Two-dimensional limit equilibrium (LE) and finite element (FE) analyses, rockfall analyses and various probabilistic assessments were conducted to evaluate various configurations of the new highwall. Following the blasting and excavation operations, ARQ Geotech conducted a lateral support design with the aim of stabilising the highwall and retaining any rocks that may come loose from the newly exposed face. The design considered additional risk associated with instabilities above and adjacent to the portals at the toe of the face of the highwall.

The works were undertaken and successfully completed with ad-hoc site inspections by the design team to ensure compliance and make appropriate adjustments where site conditions dictated a need.

Project details