Research on application of concrete pillar in conjunction with anchored bolt and cable support system

In order to further improve the recovery speed at the end of fully-mechanized mining face and reduce the moving cost of the fully-mechanized working face, the method of combining theoretical calculation, numerical simulation and field test was used for preliminary application researches on the concrete pillar support system combined with anchored bolts and cables of the pre-driven recovery room at the end of the working face. The theoretical calculation results show that the double-row layout of 250 concrete pillars with the diameter of 800 millimeters can replace the stacking supports to achieve effective external support for the main retraction channel, but the pillar top treatment needs to be done well. When the working face is mined to the remaining coal pillar 10 m, the coal body and concrete pillars on both sides of the retraction channel have obvious vertical stress concentration. When the working face is connected with the main retreat channel, the maximum compressive stress of the pillars under the four different layout schemes can reach 30.45 MPa, and the maximum tensile stress can reach 0.60 MPa. The stress of the pillars near the working face is obviously greater than that of the side away from the working face. The pillars near the working face are prone to different degrees of plastic failure, especially the shear deformations and instability failure were more likely to occur at the top and the bottom of the pillars. The layout scheme with the inter-row spacing of 1.8 m and 2 m was finally determined in consideration of the simulation results, construction procedures and construction costs. The test results show that the combined support system of concrete pillars and anchor rods (cables) could effectively control the bottom of the roof of the retraction channel. The concrete pillars maintain good integrity by virtue of the deformation and pressure of the high-density board connected to the top, which fully guarantees the equipment retraction space and provides engineering reference for the retraction of the working face equipment under similar conditions.