Abstract
In traditional vertical coal bunker systems, a coal-feeder chamber (CFC) must bear the whole weight of the bunker. However, maintenance of CFCs within soft, swelling floor rock is a challenge faced in underground coal mines. Floor-heave control is a complex problem and is still not well-solved. Moreover, there is no report on the construction of bunker without a CFC, especially under such weak floor-rock conditions. Based on the serious CFC collapse case at Xiashijie mine, China, this work analyzed the deformation characteristics, main influencing factors, and failure mechanisms of the CFC using a FLAC numerical model. The results indicate that the intrusion of water weakens the strength of the floor rock and causes significant expansive forces; thus, large deformations and tensile failure occur first in the floor, further causing shearing and tensile damage of the reinforced column and even overall instability of the CFC. Then, a new wall-mounted coal bunker (WMCB), without building the CFC, is proposed. The FLAC3D program was adopted to study the stability of the rocks surrounding the new bunker, and an optimized reinforcement scheme was determined. More importantly, a self-bearing system, which includes self-designed H-steel beams, H-steel brackets, and self-locking anchor cables, was proposed and constructed to bear the whole weight of the bunker. The stability of WMCB was verified by a theoretical safety assessment and field test. The invented WMCB could remain stable in spite of severe floor heave. This work can provide helpful references for the construction of vertical bunkers without CFCs in coal mines with soft, swelling floor rocks.
Highlights
Raw coal, produced at the working face in underground coal mines, should be transported to the surface via a transportation system (Figure 1), which commonly includes a coal strap transporting system in the longwall panel entry, coalstorage bunker installed in the mining area, conveyor belt in the main haulage roadway, coal bunker at the bottom of the shaft, and main shaft hoisting system
Based on the onsite damage features and the deformation data, the main deformation characteristics could be concluded as follows: (1) Large deformation of the floor: the cumulative rooffloor convergence was much greater than the convergence of the walls in the coal-feeder chamber (CFC), whereas the onsite deformation shows that the roof subsidence was not obvious, but severe floor heave occurred
The influencing factors and failure mode of the CFC were revealed. en, the wall-mounted coal bunker (WMCB) was designed to avoid the influence of floor heave, during which, a self-bearing system, which included H-steel beams, H-steel brackets, and self-locking anchor cables, formed a replacement for the CFC to bear the whole weight of the bunker; the whole weight was transferred to the stable and deep rocks. e stability of the new type of the coal bunker was verified in Xiashijie coal mine and made coal production therein more efficient
Summary
Raw coal, produced at the working face in underground coal mines, should be transported to the surface via a transportation system (Figure 1), which commonly includes a coal strap transporting system in the longwall panel entry, coalstorage bunker installed in the mining area, conveyor belt in the main haulage roadway, coal bunker at the bottom of the shaft, and main shaft hoisting system. The study of the existing literature for coal bunker mainly focuses on (i) the optimum bunker size and location selection in underground coal mine conveyor systems [3, 11], (ii) the construction of the coal bunker with a large diameter and vertical height [12, 13], (iii) the optimization of methods of safe construction under different geological conditions [14, 15], (iv) the deterioration and collapse mechanism of the reinforced concrete bunker [16], (v) the curing technique of blockage and fractures in the walls of the coal bunker body [17,18,19], and (vi) the maintenance of the coal bunker [20,21,22]. The security and the reliability of the new coal bunker were discussed, and it was implemented at Xiashijie coal mine
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