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Author: Admin | 2025-04-28
Blasting method. The blasting-induced cracks propagate in the predetermined direction in which case the entry roof can be well protected. Figure 15. Structural morphologies and displacement variation under different simulation conditions. (a) The narrow coal pillar mining condition; (b) Non-pillar mining using the DRF technique; (c) Non-pillar mining without using the DRF technique. Figure 15. Structural morphologies and displacement variation under different simulation conditions. (a) The narrow coal pillar mining condition; (b) Non-pillar mining using the DRF technique; (c) Non-pillar mining without using the DRF technique. Figure 16. Test processes of the DRF technique. (a) Drilling fracturing holes; (b) Charging with energy binding tubes; (c) Roof fracturing effects. Figure 16. Test processes of the DRF technique. (a) Drilling fracturing holes; (b) Charging with energy binding tubes; (c) Roof fracturing effects. Figure 17. Sketch of the field monitoring and apparatus. (a) Monitoring position and scope;(b) KJ216 monitoring apparatus for roof pressure. Figure 17. Sketch of the field monitoring and apparatus. (a) Monitoring position and scope;(b) KJ216 monitoring apparatus for roof pressure. Figure 18. Variation of the roof pressure before and after adopting the DRF technique. Figure 18. Variation of the roof pressure before and after adopting the DRF technique. Figure 19. Entry retaining effects after adopting the new technique. (a) Roof caving effects; (b) Entry retaining effects. Figure 19. Entry retaining effects after adopting the new technique. (a) Roof caving effects; (b) Entry retaining effects. Table 1. Mechanical parameters of the rock strata. Table 1. Mechanical parameters of the rock strata. Rock StrataDensity (kg/m3)Elasticity Modulus (GPa)Friction Angle (deg)Cohesion (MPa)Tensile Strength (MPa)Overlying strata250015.2301.80.7Fine sandstone265019.6322.31.2Medium sandstone260013.5342.41.4Quartz sandstone278021.1383.21.6Siltstone255016.5302.10.9No. 2-2 coal seam12504.3190.90.4Siltstone255013.9263.01.2Fine sandstone265018.8333.11.5 Table 2. Confining stresses loaded on the samples. Table 2. Confining stresses loaded on the samples. Sampleσz (Sample Faces)σx (Sample Faces)σ2 (MPa)σy (Sample Faces)σ3 (MPa)S1A & C(E & F)6.0(B & D)2.0S2A & C(E & F)6.0(B & D)1.0S3A & C(E & F)6.0(B & D)0.5 © 2017 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
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