scholarly journals Research on Roof Fracture Characteristics of Gob-Side Entry Retaining with Roof Cutting and Non-pillar Mining in Thick Coal Seam, China

2021 ◽  
Author(s):  
Mengye Zhao ◽  
Lei Zhu ◽  
Qingxiang Huang ◽  
Kai Xu ◽  
Yuyi Wu ◽  
...  
Keyword(s):  
Coal Seam ◽  
Physical Simulation ◽  
Structural Characteristics ◽  
Thick Coal Seam ◽  
Fracture Characteristics ◽  
Microseismic Events ◽  
Entry Roof ◽  
Control Layer ◽  
P Mining ◽  
Basic Roof

AbstractBased on the S1201-2 large height mining in the 2–2 coal seam of Ningtiaota colliery with on-site microseismic measurement, physical simulation and theoretical analysis methods, this paper explores the rule of roof movement in thick coal seams with roof cutting and non-pillar (hereinafter referred to as RCN-P) mining, so as to obtain scientific and effective theoretical basis for entry support and to summarize the regional structural characteristics and dynamic periodic fracture characteristics. As can be seen from microseismic events, the entry roof is featured by "two zones and one line" along the horizontal direction, namely, the crack generation area, the roof movement area. Additionally, and the obvious lateral breaking of the entry roof on the coal wall is a typical feature of the thick coal seam with RCN-P mining. The roof is vertically divided into "three zones", the crack generation area, the roof movement area and the crack development area. The roof cutting activity mainly affects the overburden activity within the basic roof height range, which is also the roof movement area. In addition, the distribution frequency and the intensity of microseismic events indicate the roof periodic breaking characteristics. The "breaking pressure relief,” “advanced crack development,” and “the limit breaking state” of roof breaking corresponds to the initial, middle, and final stage of breaking in the periodic weighting process, respectively. Compared with the normal mining, the RCN-P mining reduces the periodic weighting length and increases the pressure strength. As is shown in the physical simulation experiment, the basic roof and the cutting control layer in the "regional structural characteristics" constitute the “large” and “small” structures with RCN-P mining. The basic roof key layer is the core to control the stability of the strata, and the breaking process from the cantilever beam to the short masonry beam of the roof-cutting control layer is the main cause of the entry stress. Correspondingly, the basic structure model of “short masonry-hinged” roof was proposed and the calculation method of support was established for the entry with RCN-P mining in thick coal seam, providing a research foundation for scientific and effective rock formation control.

scholarly journals Research on Roof Fracture Characteristics of Gob-Side Entry Retaining with Roof Cutting and Non-Pillar Mining in Thick Coal Seam, China

2021 ◽  
Author(s):  
Lei Zhu ◽  
Mengye Zhao ◽  
Qingxiang Huang ◽  
Kai Xu ◽  
Yuyi Wu ◽  
...  
Keyword(s):  
Coal Seam ◽  
Physical Simulation ◽  
Structural Characteristics ◽  
Thick Coal Seam ◽  
Fracture Characteristics ◽  
Microseismic Events ◽  
Entry Roof ◽  
Control Layer ◽  
P Mining ◽  
Basic Roof

Abstract Based on the S1201-2 large height mining in the 2-2 coal seam of Ningtiaota colliery with on-site microseismic measurement, physical simulation and theoretical analysis methods, this paper explores the rule of roof movement in thick coal seams with roof cutting and non-pillar (hereinafter referred to as RCN-P) mining, so as to obtain scientific and effective theoretical basis for entry support and to summarize the regional structural characteristics and dynamic periodic fracture characteristics. As can be seen from microseismic events, the entry roof is featured by "two zones and one line" along the horizontal direction, namely, the crack generation area, the roof movement area. Additionally, and the obvious lateral breaking of the entry roof on the coal wall is a typical feature of the thick coal seam with RCN-P mining. The roof is vertically divided into "three zones", the crack generation area, the roof movement area and the crack development area. The roof cutting activity mainly affects the overburden activity within the basic roof height range, which is also the roof movement area. In addition, the distribution frequency and the intensity of microseismic events indicate the roof periodic breaking characteristics. The "breaking pressure relief,” “advanced crack development,” and “the limit breaking state” of roof breaking corresponds to the initial, middle, and final stage of breaking in the periodic weighting process, respectively. Compared with the normal mining, the RCN-P mining reduces the periodic weighting length and increases the pressure strength. As is shown in the physical simulation experiment, the basic roof and the cutting control layer in the "regional structural characteristics" constitute the “large” and “small” structures with RCN-P mining. The basic roof key layer is the core to control the stability of the strata, and the breaking process from the cantilever beam to the short masonry beam of the roof-cutting control layer is the main cause of the entry stress. Correspondingly, the basic structure model of “short masonry-hinged” roof was proposed and the calculation method of support was established for the entry with RCN-P mining in thick coal seam, providing a research foundation for scientific and effective rock formation control.

The Parameter Identification of the Steep Seam Goafs Structural Characteristics of the Coal and Rock Based on GPR

2013 ◽  
Vol 390 ◽  
pp. 403-407 ◽  
Author(s):  
Sheng Jun Miao ◽  
Chao Long ◽  
Guan Lin Huang ◽  
Han Chen
Keyword(s):  
Coal Seam ◽  
Structural Characteristics ◽  
Steep Seam ◽  
Rock Mass Structure ◽  
Thick Coal Seam ◽  
Detection Range ◽  
Rock Structure ◽  
Mining Design ◽  
Information Image ◽  
Ground Penetrating

Identifying the rock mass structure is crucial for disaster control and safe mining.In the south tunneling lane of the original +600 level, using detection method of GPR (Ground Penetrating Radar ) to implement the sophisticated detection of failure characteristics, groundwater and rock structure of the upper goaf. It determines the goaf structure parameters and water conditions through the comparative analysis of the information image. The result shows: there is no large goaf, the coal seam is broken seriously in part section and water is rich in the detection range (200m) from 2650 to 2850. The coal is hypostatic and whole in the section above 20m. It has a great significance to the safety of deep mining design and the prevention for disasters of the steep thick coal seam.

Research on the Height of Caving Zone and Roof Classification of Mining Whole Height at One Times in Thick Coal Seam

2011 ◽  
Vol 99-100 ◽  
pp. 207-212 ◽  
Author(s):  
Zhi Qiang Wang ◽  
Han Yang ◽  
Yun Bo Chang ◽  
Peng Wang
Keyword(s):  
Theoretical Analysis ◽  
Coal Seam ◽  
Main Roof ◽  
Thick Coal Seam ◽  
Key Strata ◽  
Immediate Roof ◽  
Similar Simulation Experiment ◽  
Scientific Judgment ◽  
Basic Roof

Research on the division of the overlying rock roof of stope has great significance. The existing classification method is based on the determination of existing mining height and loose coefficient , and such studies have been proved exist some limitations in the applications of thick coal seam full coal mining. Theoretical analysis and similarity simulation experiments show that during the mining all height at one times in thick coal seam, as the recovery room increase ,the thickness of immediate roof of the overlying strata which fall with the mining increased signifi-cantly, and the structure of the overlying critical layer to stabilize that is the layer of hypogyny basic roof gradually increased. Through theoretical analysis and summarizing similar simulation experiment phenomenon, based on the definition and characteristics of the immediate roof and main roof, with elastic thin mechanics and the key strata theory as the research foundation, doing scientific classification of mining face's roof in all height at one times in thick coal seam, and combined impact of all factors, which influence the breakage and caving of Basic Roof, to estab-lish a scientific judgment in the length of work face and the pressure of basic roof for practical production relations, provide certain theoretical basis.

scholarly journals Investigation on the Ground Pressure Induced by Hard Roof Fracturing at Different Layers during Extra Thick Coal Seam Mining

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Rui Gao ◽  
Jingxuan Yang ◽  
Tiejun Kuang ◽  
Hongjie Liu
Keyword(s):  
Coal Seam ◽  
Physical Simulation ◽  
Similarity Criterion ◽  
Thick Coal Seam ◽  
Failure Characteristics ◽  
Hard Roof ◽  
Ground Pressure ◽  
Working Face ◽  
Seam Mining ◽  
Roadway Deformation

The fracturing of hard roofs in different layers would result in complex ground pressure on the working face, such as supports collapsed and severe roadway deformation. However, the mechanism of the ground pressure induced by hard roof fracturing in different layers is still unclear. In the paper, a physical model of a 20 m extrathick coal seam mined with hard roofs existing was established based on the physical simulation similarity criterion. The overburden fracturing structure, abutment stress distribution, and failure characteristics of the coal body were monitored by a noncontact strain measurement system and resistance strain gauges, to reveal the mechanism of ground pressure induced by hard roof fracturing. Furthermore, on-site measurement was used to monitor and analyze the ground pressure affected by hard roofs in different levels. The results provide a theoretical basis for the control of ground pressure in extrathick coal seam mining with hard roofs.

scholarly journals Research on the Influence of Mining Height on the Movement Characteristics of Overlying Strata during Extremely Thick Coal Seam Fully Mechanized Sublevel Caving Mining

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Yongkang Yang ◽  
Jie Wei ◽  
Chenlong Wang
Keyword(s):  
Coal Seam ◽  
Physical Simulation ◽  
Quadratic Polynomial ◽  
Tensile Failure ◽  
Thick Coal Seam ◽  
Sublevel Caving ◽  
Height Increase ◽  
Supporting Force ◽  
Mining Height ◽  
Overlying Strata

The study of the effects of mining height on overlying strata movement and underground pressure characteristics during extremely thick coal seam fully mechanized sublevel caving mining is very important for choosing the reasonable mining height and the support. Based on the geological setting and mining conditions at the Xiegou Coal Mine, the results of the physical simulation test and the numerical simulation technology will be used. Some conclusions can be drawn as follows: (1) With the mining height increase, the top coal gradually converted from tensile failure to shear damage, and the coal wall gradually transformed from shear failure to tensile damage. (2) When the mining height is 7.5 m, the full-seam collapse distance, the immediate first weighting interval, and the main roof first weighting length are shorter than that when the mining height is 4m, and the periodic weighting length for the two mining heights is almost the same. (3) With mining height increase, the initial mining stage and the transition stage become shorter, and the production rates become better. (4) The law of the abutment pressure peak and the sphere of influence increase slightly, and the working resistance of support needed to be strengthened. (5) The subsidence quantity of the top coal in the control area increases along with the mining height in a quadratic polynomial way but decreases along with the initial supporting force in a negative logarithmic rule. (6) After assigning the subsidence, the regression relation between the initial supporting force and the mining height is a quadratic polynomial.

scholarly journals Analysis of Failure Mechanism of Roadway Surrounding Rock under Thick Coal Seam Strong Mining Disturbance

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Fuzhou Qi ◽  
Dangwei Yang ◽  
Yuguo Zhang ◽  
Yuxi Hao
Keyword(s):  
Coal Seam ◽  
Failure Mechanism ◽  
Strain Energy ◽  
Central Area ◽  
Surrounding Rock ◽  
Thick Coal Seam ◽  
Mining Disturbance ◽  
The Stability ◽  
Seam Mining ◽  
Basic Roof

Severe dynamic disturbance in extrathick coal seam mining has become one of the main factors threatening the stability of roadway surrounding rock. In this article, the #6 thick coal seam of Buliangou mine in Inner Mongolia, China, is taken as the engineering background. A mechanical model of the roadway roof structure is established to obtain an analytic formula of the key block subsidence. A three-dimensional discrete element model is established and used to verify the field measurement results. The fracture characteristics of the main roof above the F6104 transport roadway and the deformation and damage evolution law of the surrounding rock during thick coal seam mining are analyzed. The results show that because of the long-term breaking and falling of the roof rocks during extrathick coal seam mining, the F6104 transport roadway will undergo two severe mining disturbances at the locations of 10∼30 m and 50∼70 m ahead of the F6103 working face. During the two disturbance periods, the roadway roof displacement settles to 300∼350 mm and 750∼800 mm, and the deformation of the solid coal wall reaches 650∼700 mm and 1350∼1450 mm, respectively. The energy change curve of the total length of the fractured key roof is obtained, and when mining at 50 m, the basic roof is close to its tensile strength, and the strain energy can reach the peak value of 5.2 × 10 4  kJ, which easily leads to rock burst. The plastic damage zones on both sides of the roadway develop to the roof central area and eventually coalesce, and the deformation of the surrounding rock is obvious. When mining at 50∼70 m, the basic roof breaks and unloads, and elastic strain energy of 3.57 × 10 4  kJ is instantaneously released. These two dynamic disturbances are the main reasons for the instability of the roadway surrounding rock. The results clarify that the failure mechanism investigation of roadways in thick coal seam mining conditions can be effectively applied to control the stability of the roadway surrounding rock under strong mining disturbance.

scholarly journals Study on strata behavior law of weak cohesive roof in deep buried fully mechanized top coal caving face

2021 ◽  
Vol 267 ◽  
pp. 02032
Author(s):  
Qihan Ren
Keyword(s):  
Coal Seam ◽  
Spontaneous Combustion ◽  
Structural Characteristics ◽  
Pressure Control ◽  
Engineering Practice ◽  
Mine Pressure ◽  
Overburden Rock ◽  
Thick Coal Seam ◽  
Pressure Behavior ◽  
Step Distance

In view of the severe ground pressure behavior and spontaneous combustion risk of goaf in fully mechanized top coal caving face with deep buried weak cohesive roof and thick coal seam prone to spontaneous combustion, combined with theoretical analysis of mining overburden structure and field engineering practice, the structural characteristics of overburden rock and strata pressure behavior law are studied. The results show that: the deep buried thick coal seam fully mechanized top coal caving stope also has the phenomenon of surface step subsidence. Compared with the shallow coal seam, the surface subsidence is relatively slow, and the weak adhesion of the roof leads to the short periodic weighting step distance of the stope, and the average step distance is 9.9m. The measured peak value of advance abutment pressure is 7~10.5m in front of coal wall. According to the mine pressure control and fire prevention demand of goaf, the reasonable advancing speed is 4~5m/d.

scholarly journals Numerical Simulation Study on the Distribution Law of Deviatoric Stress of Floor under the Influence of Mining

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Hongtao Liu ◽  
Tianhong Huo ◽  
Yongen Li ◽  
Ming Luo ◽  
Guangdong Zhou ◽  
...  
Keyword(s):  
Rock Mass ◽  
Coal Seam ◽  
Structural Characteristics ◽  
Water Inrush ◽  
Gas Content ◽  
Gas Extraction ◽  
Distribution Law ◽  
Yield Model ◽  
Thick Coal Seam ◽  
Seam Mining

The Zhaogu No. 2 coal mine is a single thick coal seam mining mine with high gas content. Due to the lack of protective layer mining conditions, we can only arrange the floor gas extraction roadway (FGER) to extract the gas from the overlying coal seam of the FGER to ensure safe production. However, improper placement of FGER will cause water inrush from the floor of FGER. Given above contradictions, this paper analyzes the stress-strain relationship of the fractured rock mass in the caving zone and the stress-recovery characteristics of the goaf from the perspective of the structural characteristics of the overlying strata above goaf. Based on this, a FLAC3D numerical model of equivalent delayed filling of caving rock mass was established by using the double-yield model filling method. The distribution of floor stress under the influence of mining is obtained after the model calculation, i.e., with the increase of the distance from the floor, the ratio of bidirectional stress to the peak value, and the stability value decrease, but the decrease amplitude becomes smaller and smaller. Therefore, floor roadway used for gas extraction should be located 10-15 m below the floor. Combined with the distribution of floor strata in 11060 working face, it is finally determined that FGER should be located 13 m below the floor. Such arrangement of FGER can not only ensure the effect of gas drainage but also prevent the occurrence of water inrush from floor.

scholarly journals Cooperative Control Mechanism of Long Flexible Bolts and Blasting Pressure Relief in Hard Roof Roadways of Extra-Thick Coal Seams: A Case Study

2021 ◽  
Vol 11 (9) ◽  
pp. 4125
Author(s):  
Zhe Xiang ◽  
Nong Zhang ◽  
Zhengzheng Xie ◽  
Feng Guo ◽  
Chenghao Zhang
Keyword(s):  
Coal Seam ◽  
Cooperative Control ◽  
Field Tests ◽  
Surrounding Rock ◽  
Deep Hole ◽  
Coal Seams ◽  
Thick Coal Seam ◽  
Structure Damage ◽  
Hard Roof

The higher strength of a hard roof leads to higher coal pressure during coal mining, especially under extra-thick coal seam conditions. This study addresses the hard roof control problem for extra-thick coal seams using the air return roadway 4106 (AR 4106) of the Wenjiapo Coal Mine as a case study. A new surrounding rock control strategy is proposed, which mainly includes 44 m deep-hole pre-splitting blasting for stress releasing and flexible 4-m-long bolt for roof supporting. Based on the new support scheme, field tests were performed. The results show that roadway support failure in traditional scenarios is caused by insufficient bolt length and extensive rotary subsidence of the long cantilever beam of the hard roof. In the new proposed scheme, flexible 4-m-long bolts are shown to effectively restrain the initial expansion deformation of the top coal. The deflection of the rock beam anchored by the roof foundation are improved. Deep-hole pre-splitting blasting effectively reduces the cantilever distance of the “block B” of the voussoir beam structure. The stress environment of the roadway surrounding rock is optimized and anchorage structure damage is inhibited. The results provide insights regarding the safe control of roadway roofs under extra-thick coal seam conditions.

scholarly journals Controlling mine pressure by subjecting high-level hard rock strata to ground fracturing

2021 ◽  
Author(s):  
Rui Gao ◽  
Tiejun Kuang ◽  
Yanqun Zhang ◽  
Wenyang Zhang ◽  
Chunyang Quan
Keyword(s):  
Energy Release ◽  
Physical Simulation ◽  
Hard Rock ◽  
Structural Characteristics ◽  
Effective Control ◽  
Mine Pressure ◽  
Control Effect ◽  
Propagation Length ◽  
Ground Pressure ◽  
High Level

AbstractWhen mining extra-thick coal seams, the main cause of strong ground pressure are the high-level thick and hard strata, but as yet there is no active and effective control technology. This paper proposes the method of subjecting hard roofs to ground fracturing, and physical simulation is used to study the control effect of ground fracturing on the strata structure and energy release. The results show that ground fracturing changes the structural characteristics of the strata and reduces the energy release intensity and the spatial extent of overburden movement, thereby exerting significant control on the ground pressure. The Datong mining area in China is selected as the engineering background. An engineering test was conducted on site by ground horizontal well fracturing, and a 20-m-thick hard rock layer located 110 m vertically above the coal seam was targeted as the fracturing layer. On-site microseismic monitoring shows that the crack propagation length is up to 216 m and the height is up to 50 m. On-site mine pressure monitoring shows that (1) the roadway deformation is reduced to 100 mm, (2) the periodic weighting characteristics of the hydraulic supports are not obvious, and (3) the ground pressure in the working face is controlled significantly, thereby showing that the ground fracturing is successful. Ground fracturing changed the breaking characteristics of the high-level hard strata, thereby helping to ameliorate the stress concentration in the stope and providing an effective control approach for hard rock.

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