Vertical Stress and Deformation Characteristics of Roadside Backfilling Body in Gob-Side Entry for Thick Coal Seams with Different Pre-Split Angles

Abstract

Retained gob-side entry (RGE) is a significant improvement for fully-mechanized longwall mining. The environment of surrounding rock directly affects its stability. Roadside backfilling body (RBB), a man-made structure in RGE plays the most important role in successful application of the technology. In the field, however, the vertical deformation of RBB is large during the panel extraction, which leads to malfunction of the RGE. In order to solve the problem, roof pre-split is employed. According to geological conditions as well as the physical modeling of roof behavior and deformation of surrounding rock, the support resistance of RBB is calculated. The environment of surrounding rock, vertical stress and vertical deformation of the RBB in the RGE with different roof pre-split angles are analyzed using FLAC 3D software. With the increase of roof pre-split angle, the vertical stresses both in the coal wall and RBB are minimum, and the vertical deformation of RBB also decreases from 110.51 mm to 6.1 mm. Therefore, based on the results of numerical modeling and field observation, roof pre-split angle of 90 • is more beneficial to the maintenance of the RGE.Energies 2019, 12, 1316 2 of 16 deformation. Using the numerical simulation, break position and shape of the main roof along the RGE, the influence of different support methods on the roof movement and the relevant technical parameters of RBB were analyzed [18,19]. Tan et al. (2015) studied the stability of RBB under hard roof condition by using flexible-hard support model for RGE [20]. Zhang et al. (2015) analyzed high-water packing materials in RGE using numerical analysis, and the optimal width of the RBB was analyzed [21].There are also many studies involving problems in using the technology, such as serious deformation of RBB [22][23][24]. Using the dynamic analysis software LS-DYNA (Livermore Software Technology Corporation, Livermore, CA, USA) and theoretical analysis, Gao et al. (2013) analyzed the pressure relief mechanism of the induced roof caving by deep-hole blasting. It was found that the deep-hole-blasting can effectively reduce the load transferred to RBB and is more conducive to the maintenance of RGE [25]. Zhao et al. (2015) proposed the optimal control technology of surrounding rock structure through the following methods. First, the hard roof ahead of the working face is pre-split using deep holes. Then overhanging roof at gob side is broken so as to release the pressure by deep-hole blasting. The control technology has been successfully applied in Pingdingshan No. 12 coal mine [26]. Sun et al. studied the key parameters including height, angle, and length of deep-holes for roof breakage and pressure relief [27].However, most studies on RGE are against thin coal seam mining. It has been shown that RGE can achieve good results in thin coal seams. However, in thick coal seams using the fully mechanized longwall top coal caving (FMLTCC), the situation of the RBB is quite different. In this paper, using FLAC 3D (Itasca: Minneapolis, MN, USA), vert...

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

“…The second movement of the overlying stratum will result in stress concentration at the roof plate of the LCS and strong strata pressure behavior at the mining roadway in the lower coal seam. To prevent stress concentration in the underlying mining roadway, the temporal and spatial evolution of stress at the floor of the UCS was explored during the mining process by FLAC3D numerical analysis …”

“…To prevent stress concentration in the underlying mining roadway, the temporal and spatial evolution of stress at the floor of the UCS was explored during the mining process by FLAC3D numerical analysis. [46][47][48]…”

Determination of the key parameters of high‐position hard roofs for vertical‐well stratified fracturing to release strong ground pressure behavior in extra‐thick coal seam mining

“…[17][18][19] At present, the most commonly used technologies are coal pillar supports, gob-side entry retention, goaf filling, a spatiotemporal coupling fracturing method using a nonexplosive expansion material, water injection to weaken the roof, presplitting blasting, deep hole blasting, energy-cavity blasting, and hydraulic slitting. 2,14,15,[20][21][22][23][24][25][26][27][28] The main ideas can be summarized as follows: (a) maintain the stability of the hard roof and support the stope space; (b) weaken the hard roof and reduce its rock mass strength; and (iii) transfer the stress or release the strain energy to eliminate the source of SGP.…”

Gob‐Side Entry Retaining Technology with Advanced Empty Hole Butterfly‐Shaped Weakening in Three‐Soft Coal Seam in China

“…As a result, the gob roof is cut off along the edge of the backfill body which can effectively control the deformation and failure of the gob-side entry retaining roof. However, the amount of backfill engineering in this process is huge, requiring a large amount of manpower and material resources which increase the cost of gob-side entry retaining [8][9][10][11].…”