Geotech

Northam Platinum’s Booysendal Mine is situated about 50km north west of Mashishing (formerly Lydenburg) on the border of the Mpumalanga and Limpopo Provinces. ARQ Geotech was appointed in 2015 by DRA Global, the mine’s main EPCM contractor, as Geotechnical Consultant for the expansion project.

The mine extracts platinum and other platinum group minerals from deposits in the eastern limb of the Bushveld Igneous Complex (BIC). Northam plans to increase its current production through construction of several large infrastructure components at its new “Central Mine” complex. Several box-cuts in the valley surrounding the Groot-Dwars River will serve as portals, bringing ore to surface. The Booysendal Central Box-cut is the first of these structures. ARQ Geotech oversaw the geotechnical investigation on the proposed footprint area for the box-cut and together with DRA’s engineers set the base level of the box-cut such that the portals would be situated in competent rock – facilitating stability of portal entries. With the overall box-cut geometry set, ARQ Geotech proceeded to develop a 3D geotechnical model of the materials, and derived strength and stiffness parameters.

Conceptual design resulted in selection of a 70˚ highwall, stabilised in terms of global stability with soil nails and rock bolts up to 9.5m in length. Local stability and durability of the highwall excavation face was achieved by the application of a steel mesh reinforced, sprayed concrete facing. Detailed design was undertaken using advanced finite element analysis (FEA) of representative cross sections, backed up by simpler software and hand calculation methods, and vetted by years of experience.

Construction of the box-cut commenced in mid-2016 with ARQ Geotech providing part time site supervision to endure that the design was implemented correctly, and that quality was up to standard. The box-cut highwall stabilization was completed in late-2017 and culminated in a high wall standing proud at a height of 31m. Materials excavated were utilised to construct a large platform which will accommodate a wide range of associated surface infrastructure.

Seven decline portals were driven into the competent rock exposed at the base of the highwall. Portals were developed “on reef” from word-go, thus aiding in the cost-efficacy of the operation. To date the highwall lateral support is performing as predicted and is effectively retaining the mountainside and allowing safe entry to the reef below.

Project details