Support Design for Large Chamber Excavations: Case Study of Mechanized Deep to Ultra-Deep Level Gold Mining Available to Purchase

The development of longhole stoping mining technique involves the mechanization and increased productivity of underground bulk mining operations. Longhole stoping is usually developed with the tunnel dimensions of 15m × 15m spans. However, when mining such large chamber in deep to ultra-deep gold mining, an appropriate support design need to be taken into consideration so as to maintain the stability of the excavation. This paper provides a detailed study on the support design for large chamber excavations in mechanized deep to ultra-deep gold mining in South Africa. To achieve the objectives of the study, empirical span determination using rock mass classification methods, stability graph method and numerical modeling were used. The assessment using Q system on the hangingwall and sidewall of all the case studies shows that the ground is in good condition. Assessment using stability number has gave 20.3 and 8.6 stability numbers for the sidewall and hangingwall of the excavations respectively. Hydraulic radius results have shown that the excavations have hydraulic radius ranging from 4.6 to 7.4, depending on the dimensions of the excavation. Stability analysis also indicated that both case study A and B are within the stable zone, meaning the excavation can be stable without the installation of support tendons. Results on case studies C, D and E indicated that the excavations were within the transition zone of supported excavation and unsupported excavation. As a result, the excavations required support tendons to improve their stability. Numerical analysis on ground closure indicated a ground closure of 400mm during the extraction of primary stopes, followed by deformation of about 600mm at the first extraction of secondary stope and eventually 800mm deformation was simulated after completion of extraction. It was, therefore, concluded that the large chamber excavation can be stable for a long time.