The high and steep slope is seriously attenuated by goaf formed by mining of the transition layer at the bottom of open pit in transit to underground mining. Focused on the stability in the south slope and the main level tunnel underground in the Shouyun Mine stress, the stress and deformation are analyzed by using FLAC 3D numerical software. The results show that the failure mode of high and steep slope of an open pit transiting to underground mining differs from that of an ordinary open pit slope; a large deformation and sliding easily occur in slope as retreat mining near the foot of the pit. Large deformation and failure of high slope is proposed as the main failure mode of rock slope instability while an open pit transiting to underground mining. In order to achieve an efficient and safe mining of deep main ore, removal of upper slope and formation of an overburden cushion are proven a significant method from the open pit to underground mining.
Most domestic open-pit iron mines have entered the stage of deep mining with the depth of 500–700 m. With the increasing of mining depth, metal mines undergo a transition period from open pit to underground mining. The high and steep slope in mining transferred from open-pit to underground, will not only be affected by lithology and engineering geological conditions et al, but also closely related to underground mining methods, the study of the deformation and failure characteristics is more difficult (Yang et al. 2011).
Although lot of achievement has been made in study of open pit slope, especially the analysis of stability of slope (Sarma 1979, Zhu & Zhang 2003, Michalowski 2002, Chen et al. 2001, Zhu & Qian 2007, Yang & Yin 2003, Donald & Chen 1997, Feng et al. 2004, Xie 1996), there is a lack of study on the slope transit from open pit to underground mining. In fact, due to various differences in the properties of rock slope and geological structure, there is a large gap between the actual damage and theoretical models of high and steep slope. Zheng et al. (2001) pointed out that "Analysis of slope stability and chosen of parameter is still a big technical problem, and especially to the analysis of rock slope is still no methods for practical analysis."