A Study on the Impact of Longwall-Mining Operation on the Stability of a Slope-Pillar Structure

Hindawi Shock and Vibration Volume 2021, Article ID 9994904, 11 pages https://doi.org/10.1155/2021/9994904 Research Article A Study on the Impact of Longwall-Mining Operation on the Stability of a Slope-Pillar Structure Wenyong Bai ,1,2,3 Jie Zhang ,1,3 Bin Wang ,1,3 Jianchen Zhang,1,3 Hongru Li,1,3 and Sen Yang1,3 1School of Energy Engineering, Xi’an University of Science and Technology, Xi’an 710054, Shaanxi, China 2School of Coal Engineering, Shanxi Datong University, Datong 037000, Shanxi, China 3Key Laboratory of Western Mine Exploitation and Hazard Prevention of Ministry of Education, Xi’an University of Science and Technology, Xi’an 710054, Shaanxi, China Correspondence should be addressed to Wenyong Bai; [email protected] Received 31 March 2021; Revised 15 April 2021; Accepted 21 May 2021; Published 31 May 2021 Academic Editor: 'anh-Phong Dao Copyright © 2021 Wenyong Bai et al. 'is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 'e slope-pillar structure is defined as an artificial construction shaped by a surface highwall mining and an underground longwall mining. In order to study the impact of stress variations (induced by the longwall-mining operations) on the stability of a slope- pillar structure, No. 30101-1 working face of Nanliang Coal Mine was selected as the study subject. A series of analysis including physical similar simulation test and the theoretical analysis were conducted to study the movement pattern of the overlying strata in the working face of the slope and the loading and the stability of the pillar column revealing the mechanism of dynamic load instability of nonuniformly distributed load “slope pillar.” A “slope-pillar” reverse sliding structural model was proposed along with a newly established “slope-pillar” structural mechanical model and a formula to calculate the boundary width of the protection for the pillar under the extreme balance conditions. According to the study, the width of the protective pillar is designed at 20 m, and the roadway deformation during the working face and the stability of the pillar can satisfy the safety requirement concerning the working face, which further validates the theoretic deduction formula. 1. Introduction to the coal seaming under the slope of bedrock and sandy soil, resulting in the establishment of the depth of gully slope 'e Shenfu-Dongsheng Coal Field, as an important coal and the impacts of the slope angle on the mining pressure of energy base in China, is featured with shallow coal seams the working face [7]. Taking the coal seam conditions under and diverse topography. Since the early 1990s, scholars have the Shenfu-Dongsheng Coal Field into account, Zhang et al. conducted a series of studies on shallow coal seam mining. conducted simulation and concluded that a greater load 'e authors of [1–6] conducted a large number of on-site from the working force was imposed on the upper slope as monitoring and tests to determine the mine pressure, the the depth of the gully slope increased [8–10]. Hu et al. fracture law of the overlying strata, and strata control. Due to suggested that several factors including the existence of the the staggered surface ravines in the western region, the key strata, the depth of trench, and slope angle tended to drastic variance in the occurrence of slopes, and the in- influence the generation of dynamic loading pressure on the teraction between the special topography and the shallow working face [11]. Wang et al. established a “support-sur- coal seam mining, a series of new features such as the ap- rounding rock” model under the gully in combination with pearance of underground pressure and the movement of the the geological conditions of the mine and identified the overburden at the working face were identified. Regarding intensity of the mineral pressure following the pattern of the mining pressure and strata control under the special “back ditch section > ditch section > ditch bottom sec- topography, Xufeng et al. adopted the roof structural study tion > normal mining section” [12]. Zhang et al. established 2 Shock and Vibration the structural mechanics model of the “unevenly distributed combustion of the residual coal and 3-1 coal seam goaf, a load” of the key layer under the valley terrain and obtained comprehensive treatment area has been established with a the calculation formula of the “slide rotation load” caused by total of 5.05 ×10−2 km2 bottom area through the excavation the instability of adjacent key blocks during the movement treatment, as shown in Figure 1. of the overlying strata [13]. As shown in Figure 2, the bottom of the comprehensive 'e aforementioned studies concerning the movement of treatment area of 3-1 coal seam and No. 30101-1 working the overlying strata and mining pressure law under the special face formed a slope, which was perpendicular to the working topography during the shallow coal mining mainly focus on face. 'e slope angle is 53°. the naturally developed terrain and trenches [14]. However, due to the upper thin overlying soil layer of the shallow coal, coal outcrop often occurs around the well zone and the gully 2.2. 2e Experimental Model Design. During the study of the region, which is often treated with excavation and refilling, interaction between the overlying strata, the slope, and the resulting in manmade slope around the boundary. Current protective pillar during the advancement of the working face studies regard the man-made slopes and mining under the under the shallow coal seam slope terrain, a physical sim- man-made slope center around the sliding and instability ulation method was adopted to simulate the mining process mechanism and theories during the coordinated open-pit of the 30101-1 working face. In order to minimize the in- mining. Sun et al. studied the sliding mechanism and de- fluence of model size, the experiment adopted a geometric formation mechanism of the combined mining slope of similarity ratio of 1 :100 and established a model of 3 m in underground and open-pit mining [15, 16]. Ding et al. length, 0.2 m in width, and 0.9 m in height, as shown in proposed four stages of slope deformation and failure evo- Table 1. Considering that the main material at the pit bottom lution under the coordinated mining of open wells and of the comprehensive treatment area was dominated with revealed the deformation failure mode and instability the loose loess and gangue, some strata were removed from mechanism of mining slopes under the coupling effect of “key the comprehensive treatment area and used as the backfill hard rock layers” and “key weak layers” [17, 18]. However, the material in the model. existing research studies discussing slope slippage, overlying As demonstrated in Figure 3, the spontaneous loads of the rock movement, and coal pillar stability involved in under- overlying strata and slope instability during mining were ground mining of slopes were mainly focused on single-object monitored and recorded via the CL-YB-152 dynamic load data issues, and few discussions and studies have been performed acquisition system which was numbered from left to right to explore the coupling interaction among all three factors starting from 1. A total of 9 displacement detectors were in- during the mining process. stalled above the 3-1 coal seam to monitor the movement of 'rough the theoretical analysis and similar simula- overlying rock and slopes during mining. A number of per- tions as well as the field tests, this paper discusses the centage meters were installed on the surface and in backfill area interaction of coal pillar, overlying rocks, and slopes in the to monitor surface movement changes during the mining. 'e same space during the mining process of the manmade development of cracks and fissures during the mining was slope formed after the excavation and backfilling of the closely monitored via a BJQF-1 crack width gauge. corner coal treatment area. 'is study is expected to provide some references for mining under similar special mining conditions [19]. 2.3. 2e Movement Features of the Slope during Mining Process. During the simulation, before the mining working 2. The Movement Law of the Overlying force approached the slope, the movements observed during Strata under the Slope the mining were similar to the movements of the working face during the regular shallow coal mining. 'e mining 2.1. Project Background. As a typical loess hilly and gully triggered the initial fracture in the basic roof and a series of landform, the Nanliang Coal Mine is featured with a cyclic fractures. 'e fractured rocks were limited by the complex topography, some vertical and horizontal gullies, lateral horizontal force from the surrounding strata, deep ridges and steep ditches, gentle stratum occurrence, resulting in a relatively stable hinged structure. No inter- shallow coal seams, and simple geological structure. action was observed between the overlying strata and the 'e working face #30101 locates at the southwest of the slope during the movements under the mining. 'e loess mining field. 'e depth of the coal seam ranges from 80.43 to layer on the surface was subject to the impacts of the mining 112.01 m, with a strike length and dip length of 1398.32 m face. 'e fractures caused by the advancement of exploration and 280 m, respectively. Besides, the average thickness of the continued to expand to the surface, forming a fracture face coal seam is about 2 m. 'e transportation of the working on the vertical profile. 'e fracture face continued to develop face is close to the boundary of the minefield along the south cyclically, approaching to the slope.

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