Abstract
Small external disturbances may destabilize the bearing pillar, which in turn will change the stress distribution of the pillar supporting system, leading to its overall instability. Based on the engineering background of a mine and the mechanical analysis of pillar under disturbed stress, this paper investigated the stress, strain, and plastic zone of the pillar supporting system under different disturbed stresses. Then, the chain instability of the pillar supporting system was achieved. The law of stress transfer and plastic development of the pillar supporting system was explored. The results showed that the greater the disturbed stress, the faster the increase rate of the maximum stress of the pillar supporting system. As the width of the pillar increased, the maximum stress of the pillar decreased, so its risk of damage decreased. As the disturbed stress increased, the maximum principal strain and equivalent plastic strain of the 6 m wide pillar increased approximately linearly, and their growth rates of the 4 m wide pillar gradually increased. In the process of chain instability of the pillar supporting system, the sides of the middle pillar were destroyed first, and then the plastic zone gradually penetrated, causing the stress of the adjacent pillar to increase, which in turn led to its destruction. By analyzing the monitoring data of stress, displacement, or plastic strain, the instability of the pillar can be predicted.
Highlights
As the number of underground mines increases, so does the number of mined-out areas [1,2,3]
When the load of the roof rock layer on the pillars is close to their bearing capacity, the instability of a single pillar will inevitably cause the overall instability of the pillar supporting system
When the bearing capacity of the pillars is much greater than the load of the roof rock layer, the instability of a single pillar will not cause a chain instability of the pillar supporting system
Summary
As the number of underground mines increases, so does the number of mined-out areas [1,2,3]. The stability of the goaf directly affects the structure of the overlying strata [4,5,6]. After the goaf is unstable, the overlying strata gradually bends, sinks, and collapses and extends to the surface [7,8,9,10]. The stability of the goaf directly affects the surface buildings and the ecological environment, as shown in Figure 1 (12.25 collapse accident of Pingyi gypsum mine). The overlying strata are supported by pillars to prevent the instability of the goaf and surface collapse [11,12,13]. The stability of the goaf is mainly determined by the pillar and the roof strata. Many scholars have studied the stability of the goaf through the elastoplastic theory [14], catastrophe theory [15, 16], rheological theory [17, 18], fuzzy theory [19], and limit equilibrium theory [3, 20]
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