Surface stepped subsidence related to top-coal caving longwall mining of extremely thick coal seam under shallow cover

Ju, Jinfeng; Xu, Jialin

doi:10.1016/j.ijrmms.2015.05.003

Cited by 157 publications

(86 citation statements)

References 18 publications

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“…Prior to the determination of support capacity, the structural characteristics of key strata [25], which control the overlying strata movement, should be identified. Generally, if the key strata are close to the coal seam or the thickness of coal seam is large, the key strata will be located in the caving zone and form a cantilever beam structure (CBS), while if the key strata siting is far away from the coal seam or located in the fractured zone, it will be hinged together (i.e., the broken blocks of key strata can be hinged with each other) to form a voussoir beam structure (VBS) [24], as shown in Figure 10a.…”

Section: Determination Of Reasonable Support Capacitymentioning

confidence: 99%

“…According to the observed results of the height of the caving zone in the longwall top-coal caving face of the extra-thick coal seam in the Datong coalfield [2] and the determination method of the structure of the key strata [24], it can be concluded that the sub-key stratum (SKS) 1 of LTCC-west8101 forms the CBS, whereas the SKS 2 (main roof) forms the VBS, as shown in Figure 10b. Prior to the determination of support capacity, the structural characteristics of key strata [25], which control the overlying strata movement, should be identified. Generally, if the key strata are close to the coal seam or the thickness of coal seam is large, the key strata will be located in the caving zone and form a cantilever beam structure (CBS), while if the key strata siting is far away from the coal seam or located in the fractured zone, it will be hinged together (i.e., the broken blocks of key strata can be hinged with each other) to form a voussoir beam structure (VBS) [24], as shown in Figure 10a.…”

Section: Determination Of Reasonable Support Capacitymentioning

confidence: 99%

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Mechanism and Prevention of a Chock Support Failure in the Longwall Top-Coal Caving Faces: A Case Study in Datong Coalfield, China

Zhu

et al. 2018

Energies

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Longwall chock support failures seriously restrain the safety and high-efficiency of mining of extra thick coal seams, as well as causing a great waste of coal resources. During longwall top-coal caving (LTCC), the influential effect of the properties and the movement regulation of top-coal on strata behavior cannot be ignored, since the top-coal is the medium through which the load of the overlying strata is transferred to the chock supports. Taking Datong coalfield as an example, the mechanism of a chock support failure in the LTCC face was investigated. Research findings indicated that the hard top-coal and insufficient chock support capacity were primary reasons for chock support failure accidents. On account of the field-measured results, a new method to determine support capacity was proposed, which fully took the impact of the top-coal strength into consideration. The calculation revealed that the required support capacity had exceeded the existing production maximum, at about 22,000 KN. Since it was unrealistic to simply increase chock support capacity, other approaches, according to the theoretical analysis, were proposed, such as lowering the integrity and strength of the top-coal, and upgrading its crushing effect to weaken the support load effectively during the weighting period, which reduces the likelihood of chock support accidents occurring. Based on this, hydraulic fracturing for hard top-coal and optimization of the caving process (chock supports raised up and down repeatedly by manual operation before moving forward) were presented. The proposed solutions were successfully applied in LTCC-west8101 for subsequent mining and achieved substantial benefits. The above research provides valuable references and ideas for the control of strata behavior to ensure safe and highly efficient mining in extremely thick and hard coal seams with the LTCC method.

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Section: Determination Of Reasonable Support Capacitymentioning

confidence: 99%

Section: Determination Of Reasonable Support Capacitymentioning

confidence: 99%

Mechanism and Prevention of a Chock Support Failure in the Longwall Top-Coal Caving Faces: A Case Study in Datong Coalfield, China

Zhu

et al. 2018

Energies

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“…e hard rock strata, which have controlling e ects on the movement of overlying rock strata, are called key strata. A hard rock stratum that has a controlling e ect on a group of rock strata is called a subkey stratum, and a hard rock stratum that has a controlling e ect on its upper layer through surface strata is called a primary key stratum [8,9]. Zhu et al indicated that the position of a primary key stratum has a signi cant in uence on the height of the water owing fracture zone [10]; when the distance between the primary key stratum and the coal seam is <(7-10)M (where M is the mining height), the broken cracks in the primary key stratum will run through to become water owing fractures, and the water owing fracture zone would be developed at the bedrock top.…”

Section: Height Of the Gas Flowing Fracture Zonementioning

confidence: 99%

Horizontal Subzone Characteristics and Methane Seepage Properties of the Gas Flowing Fracture Zone above the Gob

Qin

2018

Advances in Civil Engineering

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Gas flowing fracture zone (GFFZ) is an active zone in the gob where pressure-relieved methane can move freely. However, there are very few research findings on the horizontal development characteristics and internal methane seepage properties of GFFZs. In this paper, based on the development height of a GFFZ above the gob, the GFFZ was horizontally divided into the following: a lateral fracture subzone, an O-ring fracture subzone, and a compacted subzone. e identification criteria for all of these horizontal subzones were given by analyzing the influence of the stress in the coal rock mass on the development of mininginduced fractures. A numerical simulation study was conducted to determine the influences of the mining height and mining depth on the morphological development of all horizontal subzones of the GFFZ, and the simulation results showed that the mining height was the main factor influencing the development characteristics of horizontal subzones of the GFFZ. Both the maximum distance of the lateral fracture subzone beyond the mining boundary and the width of the O-ring fracture subzone increased with the increase of mining height. A physical simulation experiment was performed for extraction of gob methane through a surface borehole, and the experimental results showed that the gas flow state was laminar within the range of the lateral fracture subzone and the compacted subzone but that the gas flow state was turbulent, not following Darcy's law, within the range of the O-ring fracture subzone.

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“…For instance, Zhang et al investigated the height of fracture zone in overburden in studies focusing on aquifer protection during longwall mining of shallow coal seams [5,6]. Ju and Shi, et al, respectively, studied the characteristics of mining-induced surface subsidence and fractures in overburden above an ultra thick coal seam [7,8]. Their results can be used as reference for safe mining of ultra thick seams occurring in western China.…”

Section: Introductionmentioning

confidence: 99%

Influence of Spatial Relationships between Key Strata on the Height of Mining-Induced Fracture Zone: A Case Study of Thick Coal Seam Mining

Wang

Cao

et al. 2018

Energies

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Abstract:The behavior of the overburden of working face 20104 at the Wangjialing coal mine was investigated using borehole imaging. The measured height of the conductive fracture zone (CFZ) in the overburden, 148 m, is significantly different from the height that is predicted by an empirical formula. The spatial relationships between key strata (KS) required for their fracturing and their influence on the CFZ's height were analyzed. The results demonstrate that the spatial relationships between adjacent KS are a major factor behind the abnormal increase in the height of CFZ relative to the coal seam. The height of linkage (HoL) between KS was introduced and an equation for calculating this height was proposed. The study found that the fracturing of a KS could induce fracturing of the adjacent KS above it if their height difference was smaller than the HoL between them. Otherwise, the fractures resulting from the lower KS would terminate at the bottom of the higher KS. When the location of a high KS satisfies certain requirement, the spatial linkage between adjacent KS will allow for the conductive fractures arising in a lower KS to propagate through the high KS as well as the strata controlled by it, thus increasing the height of CFZ in overburden.

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Surface stepped subsidence related to top-coal caving longwall mining of extremely thick coal seam under shallow cover

Cited by 157 publications

References 18 publications

Mechanism and Prevention of a Chock Support Failure in the Longwall Top-Coal Caving Faces: A Case Study in Datong Coalfield, China

Mechanism and Prevention of a Chock Support Failure in the Longwall Top-Coal Caving Faces: A Case Study in Datong Coalfield, China

Horizontal Subzone Characteristics and Methane Seepage Properties of the Gas Flowing Fracture Zone above the Gob

Influence of Spatial Relationships between Key Strata on the Height of Mining-Induced Fracture Zone: A Case Study of Thick Coal Seam Mining

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