Abstract
This paper takes the double predriven recovery rooms (DPRR) of 31109 panel of a coal mine in Inner Mongolia as a case study. DPRRs are used to withdraw mining equipment, which play a significant role in safe and efficient production in the final longwall mining stage. Theoretical analysis and numerical simulation were carried out to study the reasonable size of the front abutment pillar between DPRR (inter-DPRR pillar) and the damage depth of the DPRR floor. The results show that (1) the stress distribution of the fender (the remnant longwall panel) can be approximately divided into three stages with the advance of the working face: stress redistribution (the first) stage, stress superimposed growth (the second) stage, and stress transfer (the third) stage. (2) According to stress distribution and the corresponding failure mode of the fender, the calculation model of the slippage damage of the DPRR floor is rectified, and the damage range of the floor is rezoned to make it more suitable for the damage depth of the room. (3) The zone of influence of the front abutment pressure is 40–50 m, and the stress around the DPRR increases significantly in the final mining stage. When the size of the inter-DPRR pillar is greater than 15 m, the effect of increasing the coal pillar size on lowering the peak stress of the main predriven recovery room is limited. (4) Floor heave tends to increase at first and then decrease with depth and reaches the maximum in the depth of 5 m in the final mining stage, indicating that 5 m is the starting point for the initial depth of the floor heave. (5) The theoretical calculation shows that the reasonable size of the inter-DPRR pillar is 20 m, and the critical width of the fender is 18.48 m, which can guide the secondary support to prevent dynamic disasters. Floor grouting and constructing concrete floor are effective and economic ways to control the floor heave.
Highlights
Double predriven recovery rooms (DPRRs) play a significant role in safe and efficient production in the longwall mining final stage [1,2,3]
It shows that the front abutment pressure, peak stress of the fender, and inter-DPRR pillar increase with longwall mining. e slope of the front abutment pressure growth starts to reduce when the working face advances 60–70 m, and the peak stress of the fender is greater than the peak stress of the interDPRR pillar when the working face advances about 65 m
Mining distance of working face: m m m m m (a) the DPRR floor in the final mining stage. e following conclusions are obtained: (1) e fender stress distribution can be approximately divided into three stages: stress redistribution stage, stress superimposed growth stage, and stress transfer stage
Summary
Double predriven recovery rooms (DPRRs) play a significant role in safe and efficient production in the longwall mining final stage [1,2,3]. Liu et al [11] carried out physical simulations to study the sudden closure of hydraulic supports when the working face crossed the abandoned roadway and investigated the distribution of front abutment pressure and failure characteristics of the surrounding rock. Xie et al [16] established a structural model of the main roof during crossing abandoned roadway, gained the critical working resistance of support under the long key block, and studied the stress distribution and failure characteristic of the surrounding rock using numerical modelling. Wang et al [26] conducted a numerical method to systematically simulate the laws of stress evolution, failure, and roadway deformation of inter-DPRR pillar with the different widths under the secondary mining influence.
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