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Dip-angle-effect-based deformation and failure law of steeply dipping stope roofs with large mining heights

Xie Panshi, Huang Baofa, Wu Yongping, Luo Shenghu, Wang Tong, Yan Zhuangzhuang, Chen Jianjie

Archives of Mining Sciences

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2023

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Vol. 68, no. 3

507--524

EN

The deformation and failure law of stope roofs is more complicated than horizontal coal seams affected by the angle of the coal seam during the mining process of steeply dipping coal seams. This study focused on and analysed the working face of a 2130 coal mine with steep dipping and large mining height. Through the use of numerical calculation, theoretical analysis, physical similar material simulation experiments, and field monitoring, the distribution characteristics of roof stress, as well as the threedimensional caving migration and filling law, in large mining height working faces under the dip angle effect was investigated. The influence mechanism of the dip angle change on the roof stability of large mining heights was investigated. The results revealed that the roof stress was asymmetrically distributed along the inclination under the action of the dip angle, which resulted in roof deformation asymmetry. With the increase in the dip angle, the rolling and sliding characteristics of roof-broken rock blocks were more obvious. The length of the gangue support area increased, the unbalanced constraint effect of the filling gangue on the roof along the dip and strike was enhanced, and the height of the caving zone decreased. The stability of the roof in the lower inclined area of the working face was enhanced, the failure range of the roof migrated upward, and the damage degree of the roof in the middle and upper areas increased. Furthermore, cross-layer, large-scale, and asymmetric spatial ladder rock structures formed easily. The broken main roof formed an anti-dip pile structure, and sliding and deformation instability occurred, which resulted in impact pressure. This phenomenon resulted in the dumping and sliding of the support. The ‘support-surrounding rock’ system was prone to dynamic instability and caused disasters in the surrounding rock. The field measurement results verified the report and provided critical theoretical support for field engineering in practice.

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Internal mechanism of asymmetric deformation and failure characteristics of the roof for longwall mining of a steeply dipping coal seam

Luo Shenghu, Wang Tong, Wu Yongping, Huangfu Jingyu, Zhao Huatao

Archives of Mining Sciences

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2021

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Vol. 66, no. 1

101--124

EN

Stability control of the roof is the key to safe and efficient mining of the longwall working face for a steeply dipping coal seam. In this study, a comprehensive analysis was performed on the roof destruction, migration, and filling characteristics of a steeply dipping longwall working face in an actual coalmine. Elastic foundation theory was used to construct a roof mechanics model; the effect of the coal seam inclination angle on the asymmetric deformation and failure of the roof under the constraint of an unbalanced gangue filling was considered. According to the model, increasing the coal seam angle, thickness of the immediate roof, and length of the working face as well as decreasing the thickness of the coal seam can increase the length of the contact area formed by the caving gangue in the lower area of the slope. Changes to the length of the contact area affect the forces and boundary conditions of the main roof. Increasing the coal seam angle reduces the deformation of the main roof, and the position of peak deflection migrates from the middle of the working face to the upper middle. Meanwhile, the position of the peak rotation angle migrates from the lower area of the working face to the upper area. The peak bending moment decreases continuously, and its position migrates from the headgate T-junction to the tailgate T-junction and then the middle of the working face. Field test results verified the rationality of the mechanics model. These findings reveal the effect of the inclination coal seam angle on roof deformation and failure and provide theoretical guidance for engineering practice.

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Deformation and failure mechanisms and support structure technologies for goaf-side entries in steep multiple seam mining disturbances

Xie Panshi, Wu Yongping

Archives of Mining Sciences

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2019

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Vol. 64, no. 3

561--574

EN

Entries in steeply pitching seams have a more complex stress environment than those in flat seams. This study targets techniques for maintaining the surrounding rock mass stability of entries in steep seams through a case study of a steep-seam entry at a mine in southern China. An in-depth study of the deformation and instability mechanisms of the entry is conducted, employing field measurement, physi-cal simulation experiment, numerical simulation, and theoretical analysis. The study results show that the surrounding rock mass of the entry is characterised by asymmetrical stress distribution, deformation, and failure. Specifically, 1) the entry deformation is characterised by a pattern of floor heaving and roof subsidence; 2) broken rock zones in the two entry walls are larger than those in the roof and floor, and the broken rock zone in the seam-floor side wall is larger than that in the seam-roof side wall; 3) rock bolts in the middle-bottom part of the seam-floor side wall of the entry are prone to failure due to tensile stress; and 4) rock bolts in the seam-roof side wall experience relatively even load and relatively small tensile stress. Through analysis, disturbances were found to occur in both temporal and spatial dimensions. Specifically, in the initial mining stage, the asymmetrical rock structure and stress distribution cause entry deformation and instability; during multiple-seam multiple-panel mining operations, a wedge-shaped rock mass and a quasi-arc cut rock stratum formed in the mining space may cause subsidence in the seam-floor side wall of the entry and inter-stratum transpression, deformation, and instability of the entry roof and floor. The principles for controlling the stability of the surrounding rock mass of the entry are proposed. In addition, an improved asymmetrical coupled support structure design for the entry is proposed to demonstrate the effective control of entry deformation.

PL

Chodniki w wyrobiskach biegnących po upadzie charakteryzują się bardziej złożonym rozkładem naprężeń niż wyrobiska poziome. Celem niniejszej pracy jest zbadanie technik stabilizowania górotworu w otoczeniu chodników nachylonych na podstawie studium przypadku chodnika o dużym stopniu nachylenia w jednej z kopalń w południowych regionach Chin. Przeprowadzono dogłębną i szczegółową analizę mechanizmów powstawania odkształceń i niestabilności w wyrobisku w oparciu o pomiary w terenie, eksperymenty w symulowanych warunkach fizycznych, symulacje numeryczne oraz analizy teoretyczne. Uzyskane wyniki wskazują, że górotwór w bezpośrednim otoczeniu chodnika charakteryzuje się asymetrycznym rozkładem naprężeń, odkształceń oraz pęknięć. W szczególności, analiza odkształceń wskazuje: 1) występowanie pęcznienia spągu oraz osiadania stropu, 2) strefy spękań skał w obydwu ścianach bocznych chodnika są większe niż strefy spękań w spągu i stropie, a strefa spękań w ścianie bocznej od strony spągu jest większa niż w pobliżu stropu; 3) podpory kotwiące w części środkowej ściany wyrobiska od strony spągu mają tendencje do pękania wskutek naprężeń rozciągających; 4) naprężenia działające na kotwy stabilizujące ścianę boczną chodnika w części bliżej stropu są stosunkowo równomierne, z kolei występujące naprężenia rozciągające są relatywnie niewielkie; Analizy wykazały występowanie zaburzeń zarówno w ujęciu czasowym jak i przestrzennym. Na etapie rozpoczęcia prac wydobywczych odkształcenia i niestabilności chodnika powstają wskutek asy-metrycznej struktury skał i asymetrycznego rozkładu naprężeń; w trakcie prac wydobywczych obejmujących wybieranie ścian w kilku polach powstają obszary warstw skalnych górotworu w kształcie klinów i łuków, co prowadzić może do osiadania ścian chodnika w pobliżu spągu, od strony wybieranego złoża, a także do zachodzenia na siebie warstw skalnych, odkształceń i niestabilności spągu i stropu w wyrobisku. W pracy zaproponowano zasady stabilizowania górotworu w otoczeniu wyrobiska. Ponadto, zaproponowano udoskonalony projekt zmodyfikowanego asymetrycznego wspornika podporowego do zainstalowania w chodniku, dla zademonstrowania skutecznej metody kontrolowania odkształceń wyrobisk chodnikowych.