ABSTRACT
Ore pillar is not entirely ideal homogeneous rock. Pillar strength is influenced by many factors such as mining disturbance, crustal stress etc. Pillar inevitably exists weak structure such as joints and fracture, however, that does not mean that the pillar completely lose carrying capacity. During pillar standing, micro cracks develop in the process
1 INTRODUCTION
The exploitation of mineral resources will leave plenty of goaf. As time elapse, the mined-out areas subject to the overall collapse due to the weathering and rheological factors (Wang et al. 2011, Wang et al. 2010). There are many large scale goaf collapse reports at domestic and abroad (Caquot & Kerisel 1948). Because of the complicity of geological condition, and improper design and management, lot of the pillars with irregular shape and distribution remained in mined out area in China. For example, Guangxi HepuHengdagypsum mine, Gansu Changba Lead-zinc Mine, Tongling Shizishan copper mine, Henan Luanchuan molybdenum deposit, Yunnan Lanping lead-zinc mine (Ma & Xie 2013), etc. The mined-out areas deteriorate mining conditions, bring the serious effect on mine production and safety.
