Characteristics of Strata Behavior during Thick Seam Mining by Fully-Mechanized Top Coal Caving in a Loess-Covered Gullied Region

Abstract

This study systematically investigates the overburden movement and strata behavior at a fully-mechanized top coal caving (FMTCC) face in a thick coal seam in a loess-covered gullied region by field measurement and theoretical analysis. A comparative analysis was performed to examine how the attitude of surface gullies and the structure of overburden affect face support resistance. The characteristics and evolution mechanism of strata behavior during FMTCC under gully slopes in a loess-covered gullied region were discovered through a mechanical analysis of the roof structure and a comparison to the mining of a typical shallow seam under gully slopes. The study found that as the FMTCC face advanced, the strata behavior initiated in the middle part of the face and then continued to both ends, and its intensity was higher in the middle part than in the upper and lower parts. During mining under gullies, the increases in support resistance were generally less than 5% (except for the maximum increases of 7-9%), indicating that the occurrence of gullies on the surface had little influence on the strata behavior at the FMTCC face. Due to the increased burial depth and the number of key strata, the roof at the FMTCC face under gullies formed a stable load-bearing structure called a voussoir beam, which was the key difference from the strata behavior characteristics in the shallow mine under gullies.

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.…”

Determination of working resistance based on movement type of the first subordinate key stratum in a fully mechanized face with large mining height

“…Due to the movement of the 4th siltstone of SKS 1 being that of a voussoir, and h 2 = 24 m. By substituting the aforementioned parameters of the working face into inequality (31), it is clear that inequality (31) is not satisfied. Therefore, it can be deduced that the breaking of SKS 2 does not influence SKS 1; the support working resistance of LW30101 should thus be calculated according to formula (34).…”

“…Many studies were performed on the aforementioned issues related to FMFLMH, and their results have indicated that the key to solving the aforementioned issues is to determine the support working resistance of the working face. [26][27][28][29][30][31] For example, Gong and Jin 26 established two calculation models of support working resistance under a voussoir beam structure and the cantilever structure of SKS 1 to determine working resistance in FMFLMH. In the empirical formula method, empirical estimation formulae (Table 1), are used to calculate the support working resistance of the longwall faces with normal mining height 20 ; however, with the increase in extraction height, especially FMFLMH, determination of the support working resistance by empirical estimation cannot guarantee safe mining of the face.…”

“…[23][24][25] In particular, the structural form and movement type of SKS 1, and many theoretical calculation models for the support load have been established to determine support working resistance in FMFLMH. [26][27][28][29][30][31] For example, Gong and Jin 26 established two calculation models of support working resistance under a voussoir beam structure and the cantilever structure of SKS 1 to determine working resistance in FMFLMH. Yan et al 27 point out that the roof strata are prone to forming the short cantilever structure of SKS 1 and the voussoir beam structure of SKS 2, and presented formulae for the support working resistance under this structural condition in FMFLMH.…”

Dynamic Random Arching in the Flow Field of Top-Coal Caving Mining

“…In China, fully mechanized top-coal caving mining in ultra-thick coal seams (especially in 14-20 m ultra-thick coal seams) has developed rapidly in the past 10 years [1][2][3][4]. Studies in topics such as equipment matching, wall stability, strata control technology, safety guarantee technology for low gas occurrence and high gas emission have made important progress [5][6][7][8][9][10][11].…”