A Case Study on Optimization and Control Techniques for Entry Stability in Non-Pillar Longwall Mining

Abstract

In order to reduce large deformation failure occurrences in non-pillar longwall mining entries due to roof weighting behaviors, a case study in Halagou coal mine was conducted on optimization and control techniques for entry stability in non-pillar longwall mining. The Universal Discrete Element Code (UDEC) modeling was adopted to study entry stability in non-pillar mining, and the characteristics of deformation and stress and crack propagation were revealed. The large deformation transmission between the entry-immediate roof and the gob-immediate roof could be eliminated by optimizing the entry roof structure through a directional roof-cutting method. The localized tensile stresses generated in the entry-surrounding rock caused the generation of coalescent macroscopic fractures, which resulted in the instability of the entry. The tensile stress state could be inhibited by an active flexible support system through enhancing the confining pressure on the surrounding rock. Serious rotation subsidence occurs in the entry roof due to periodic weighting of the main roof, which could be greatly reduced by a passive rigid support pattern. The numerical and field test results both showed that the roof weighting pressure was offloaded by the technique and that the deformation of the entry surrounding the rock in non-pillar mining was quite small. Thus, the technique can effectively ensure the stability of the gob-side entry, which can provide references for entry stability control in non-pillar longwall mining.

Study on the movement characteristics of the overlying stratum and surrounding rock control in ultraclose coal seams: A case study

“…Mining activity at a single longwall face in the UCS will cause destruction of the old roof stratum following a vertical "O-X" pattern, after which a "masonry beam" structure will form in the overlying stratum. [26][27][28][29][30][31] As demonstrated by a considerable number of studies, [31][32][33][34][35][36][37] the mining activities at multiple longwall faces will enlarge the fracture zone of the overlying stratum when the coal seam is deeply buried. In this case, the key layers located in the upper middle part of the fracture zone far away from the coal seam may experience rotation or fracturing and become unstable.…”

“…The surface displacement of the roadway is an important indicator for assessing its reasonable location and supporting effect. 32,50 To validate the supporting performance on the roadway, several measurement stations were arranged in the haulage roadway 1007 in LCS. The surface displacement recorded from a typical measurement station is shown in Figure 15.…”

Mine Pressure Behavior Characteristics and Control Methods of a Reused Entry that Was Formed by Roof Cutting: A Case Study

“…Later, the main roof regularly cycles in the form of semi-"O-X" type failure and forms fractured rocks, resulting in a significant stress concentration in the coal body [19,20], as shown in Figure 3(a). To date, many research studies have studied the deformation characteristics, stress distribution, and control countermeasures of the reused entry during the mining process of the first working face [14,21], so these will not be further described here. is work mainly aimed at observing the stress distribution and deformation characteristics of the reused entry during the mining process of the second working face.…”

Coal Mine Abutment Pressure Distribution Based on a Strain-Softening Model

“…Ma calculated the plastic zone radius and stress of mining entries with a mechanic model based on the full strain-stress curve [5,6]. Zheng and Yang calculated the width of the coal rib damaged zone with a simplified rib stress distribution [7,8]. Li, Pan, and Wang studied the influence of the support zone on the plastic zone of the coal with grouting-bolting combined support on coal ribs [9][10][11].…”