The mechanism of decrease in bearing capacity and performance evaluation of the yielding bolt in coal mine

Abstract

With the increase of the coal mining depth, the surrounding rock shows characteristics of high stress and large deformation. However, the traditional bolt could not adapt to this surrounding rock environment and become invalid due to low elongation. In order to solve the problem, the new type of yielding bolt has been designed. It could release the deformation energy of the surrounding rock through its yielding pipe. However, few studies have been reported on the mechanism in bearing capacity decrease of the yielding pipe. Furthermore, the evaluation of the yielding bolt was not fully understood. Under such a background, a numerical model of the yielding model was established. According to the numerical simulation, the mechanism of the decrease in the bearing capacity of the yielding bolt is that the buckling occurs at different positions of the yielding pipe, making the material stiffness matrix turn negative, and the bearing capacity decreases significantly. Also, the performance of the yielding bolt could be evaluated from the use efficiency of the yielding pipe, the plastic strain characteristics of the components of the yielding bolt, and the energy absorption law. The evaluation results indicated that: (a) the deviation of the yielding pipe's Mises stresses was within the range of 1.0%‐4.0%. The stresses were distributed evenly, and the material use efficiency was high; (b) only the yielding pipe occurred the plastic failure during the yielding process, and other components were at the elastic stages. After the yielding, the yielding bolt was still effective for support. (c) The yielding pipe could absorb energy smoothly, which is helpful for the stability of the yielding bolt.

Failure mechanism and divisional differentiated control of surrounding rock in mining roadway under remaining coal pillar in close‐distance coal seam

“…They analyzed the tension state of its stress, which effectively guided the reasonable recovery of the shallow-buried close-distance coal seam. Tai et al [8][9][10][11] put forward the grouting and multicomponent combined support control method to solve the severe deformation of the large crosssection roadway under the goaf of the extra-thick coal seam, which played a good effect on the surrounding rock control of the roadway under the goaf. Lv et al 12 discussed the deformation and failure characteristics of the retracement channel under different overburdened environments in the close-distance coal seam.…”