A construction section from elevation -930m to -1271m of a 1527m deep shaft in Xincheng Gold Mine was selected as case study.

Combining rock mass quality classification and the failure depth of the surrounding rock around a shaft temporary support parameters were determined, and its safety was evaluated using empirical methods and numerical simulation method.

Considering stress adjustment and energy releasing in surrounding rocks fully, it was put forward an energy pre-released support technology. Timing for permanent support and the height from concrete to working face were comprehensively determined from the two perspectives of the minimum space and time requirements. Finally, the safety of the concrete lining and the overall stress control effect was assessed. The results show that the provided energy pre-released support technology can help reduce the stress concentration and the risk of instability or rock burst, so as to maintain the long-term stability, and it should be adopted for deep shaft supporting under high stress conditions.

1 Introduction

It is well known that the shaft is the throat of underground mining production system. It is usually a major infrastructure project and one of the most difficult sub-projects in underground mine construction. Compared to shallow shafts, the geological conditions and stress state of deep shafts are more complicate, especially under the action of strong excavation unloading. With the increasing depth and polytropic strata the stress condition will cause more complicate mechanical response mechanisms and distinct different mechanical response characteristics. So, it will cause much doubt if the design method and construction technology in shallow shaft engineering are directly applied to the deep shaft construction. In a word, the design method and construction technology of deep shaft need to be changed compared to shallow.

With the increasing of shaft excavation depth, the in-situ stress in the surrounding rocks will increase. This will induce rapid stress adjustment and high stress concentration in transverse or longitudinal direction in the local surrounding rock, due to excavation unloading. Once the compressive shear stress caused by the surrounding rocks exceeds its strength, it will produce fracture, fragmentation, plastic expansion, rock burst, etc (Zhang Xiaochun and Wang Junqiang 2007; Yin Youquan et al 2014). As a result, the geological environment of the surrounding rocks of the shaft is further deteriorated. The deformation and failure will be strong inelastic failure instead of simply controlled by structural plane, especially with the increasing influence of horizontal tectonic stress, blasting disturbance and other nonlinear loads. Therefore, it will have a great significance to study how to carry out effective stress adjustment and support design under high stress and strong excavation unloading, in order to provide the basic theoretical support for the long-term stability of a deep shaft.

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