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ABSTRACT: In order to improve effectiveness, safety and economy of protection layer mining, elasto damage constitutive model of coal and rock mass was constructed based on Mole-Coulomb criterion. Using damage variable as transition, coal and rock mass permeability-damage evolution equation was also built. Then, using mining rock mechanics, percolation mechanics and damage mechanics, gas seepage-stress-damage coupling model of mining coal and rock was constructed. And the elasto plastic damage constitutive model was verified by numerical simulation program through FLAC. At last, gas seepage behavior under long distance protective later mining in Gu Qiao Coal Mine was studied through the elasto plastic damage constitutive model. Results showed that under influence of mining, permeability coefficient of protected seam was 1760 times of the original value and gas pressure deduced from 2.8 MPa to 0.6 MPa. Coal and gas outburst hazard was eliminated. Numerical simulation results were basically consistent with actual situation which indicated that the elasto damage constitutive model and gas seepage-stress-damage coupling model can be used to describe coal seam damage and its permeability change. This result has guiding significance on feasibility of protection layer mining, effect pre-evaluation of pressure relief gas extraction in protected seam and optimization of pressure relief gas extraction technology. 1 INTRODUCTION Protection layer mining and gas extraction in pressure releasing area of protected seam are the most effective, economic and reliable outburst prevention technique. They are also compulsory and prior method for coal seams with outburst danger in national regulation (Cheng et al. 2003, Chen et al. 2004, State Administration of Coal Mine Safety 2009, Yu et al. 2004). Tang Chunan, Liu Hong-yong and Wang Deng-ke have built damage constitutive model of coal and rock mass (Liu et al. 2010, Wang et al. 2010, Yang et al. 2005, Yang et al. 2001). They studied evolution behavior between stress, damage and permeability evolution during coal mass deformation under protection layer mining. The achievement provides basis for study on coal mass deformation behavior and gas seepage behavior under protection layer mining.
Study on Abutment Pressure in Thick Coal Seam Under the Compound Key Strata
Xu, M. G. (Xi'an University of Science and Technology) | Dong, K. Q. (Xi'an University of Science and Technology) | Pan, H. Y. (Xi'an University of Science and Technology) | Li, S. G. (Xi'an University of Science and Technology) | Han, J. Z. (Xi'an University of Science and Technology)
ABSTRACT: The existence of the overlying compound key strata would cause stress distribution in surrounding rock, breaking of the key strata and the periodic weighting of a mining face, which are also related to variation of the mining height. Based on the compound key strata theory, the simplified mechanical model of the compound key strata before breaking is established for the fully mechanized top coal caving mining of thick coal seam. Through calculation, the computational expressions of equivalent load of the upper strata and the ultimate breaking step of the key strata is obtained. By using the FLAC numerical software, the abutment pressure under the compound key strata during fully mechanized caving of thick coal seam is simulated, and the calculated breaking of the compound key strata, periodic weighting, stress concentration area etc. agree with in situ observation. 1 INTRODUCTION When there are two or more key layers of hard rock bed in overlying strata whichever upper or lower, the interaction in terms of the compound effect will affect the deformation and breaking behavior during coal mining (Miu et al. 1999). Qian, Miao, Mao etc (Miu et al. 1999, Mao et al. 1999, Sun et al. 2005), defined the basic concept of the compound key strata the compound effect, and simulated the influence of compound effect by discrete element, which provided foundation of discrimination of compound effect. The study (Mao et al. 1999) showed that the ultimate breaking length L of the key strata had an inverse relationship with the mining height b, indicating that mining height had significant influence on the breaking of the key strata, stress distribution of surrounding rock and periodic weighting. Based on the compound key strata theory, the affecting scope of abutment pressure and periodic weighting in the fully mechanized top coal caving mining face of thick coal seam under the compound key strata in Binchang are analyzed by using theoretical calculation and FLAC numerical simulation, the result agreed with field test data. This study provides a theoretical and instructive guide to select the support type, and so on.
ABSTRACT: The vertical stress, failure patterns and deformation of roadway surrounding rock under different coal pillar width are studied by using FLAC software. The results show that with the increase in the width of coal pillar, stress concentration range and factor in pillar decreases, gradually showed uniform bearing form, at the same time, the displacement of roadway and plastic zones in pillar gradually decrease. With the increase of the width of coal pillar, the range of elastic core is larger, indicating that the more stable the roadway coal pillar is, the more safety will be. Taking into account that large coal pillar width would result in the waste of resources, the reasonable coal pillar width is between 14–16 m. 1 INTRODUCTION According to numerous studies on the rational section coal pillar, many effective methods to determine the reasonable size of coal pillars can be categorized as follows (Cui et al. 2012, Tu et al. 2011, Zhang & Shi 2004, Chen 2014, Shao et al. 2014): 1) Mathematical statistics, a large number of measured results give rise to inductive reasoning that unstable surrounding rock conditions of coal pillar size; 2) Application of mine pressure regularity with various coal pillar and empirical formula to analyze the reasonable size of the coal pillar; 3) The reasonable coal pillar width range determined based on measured pillar abutment pressure distribution method analysis of coal seam; 4) According to the limit equilibrium theory to derive the coal hold steady when the width formula; 5) The estimation formula of three dimensional plastic zone width of coal pillar stress. The numerical simulation of roadway surrounding rock is performed to analyze the width of coal pillar under different stress and movement for working face 222203 in Shuangxin Mining Co. coal mine, Inner Mongolia.
The Deformation Mechanism of Soft Coal Roadway Under Mining Activity Influence and Its Support Technology
Sun, Z. G. (Chongqing Research Institute) | Li, S. G. (China Coal Research Institute, Beijing) | Li, L. H. (Chahasu Coal Mine, Investment Inner Mongolia Energy Co. Ltd., China Electric Power Construction and Investment) | Tian, L. T. (Chahasu Coal Mine, Investment Inner Mongolia Energy Co. Ltd., China Electric Power Construction and Investment)
ABSTRACT: In light of the coal roadway deformation in soft rock conditions under dynamic pressure influence, this research was made on the governance practices in No. 3101 working face, combined theories and computer numerical simulation, the floor heave and spalling mechanism under the influence of multiple mining activities were analyzed and a rational pillar size was calculated and bolt-cable coupling improvement support projects were designed on the basis of the original support plan. The study result shows that it was expansion-flexural composite of floor heave and rib spalling affected by coal pillar size. It can effectively control the volume expansion at the roadway bottom plastic zone and reduce the impact of the surrounding rock pressure of two sides on the floor by increasing coal pillar size to 25 m and using "add floor rock bolt and increase support density in two sides of roadway and enlarge anchor length" comprehensive reinforced support means. 1 INTRODUCTION For a long time, the problem of soft rock roadway supporting is always one of the major technical hurdle which seriously influence the coal production safety in China coal mines (He & Sun 2004, Qian & Shi 2003). Influenced by soft rock and engineering stress disturbed, there were large-scale rib spalling and floor heave issues during mining in No. 3101 work face, and they are seriously restricting the safety production of coal mine (as shown in Fig. 1). In allusion to the problems mentioned above, the deformation mechanism of soft coal roadway was analyzed and an improved roadway support design scheme was proposed by combining the theories and computer numerical simulation. 2 ENGINEERING GENERAL SITUATION The No. 3101 long-wall fully-mechanized working face with large mining height is the first mining face in Chahasu coal mine, its buried depth is 398.8 m and the thickness is 6.45 m. Structures in zonation are simple and dip angle of coal seam is 1~3°. The roof rock was composed of mudstones, sandy-mudstones and medium grain sandstones. Among them, the medium grain sandstone is the main roof and its thickness is about 12.55~24.85 m. The immediate floor of coal seam is carbon mudstone with a thickness of 0.85~1.8 m, the main floor is consisted of coarse-grained sandstones and its thickness is 5.35–14.18 m.
- Research Report > New Finding (0.34)
- Research Report > Experimental Study (0.34)
- Geology > Rock Type > Sedimentary Rock > Organic-Rich Rock > Coal (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (1.00)
Research on Elliptic Fracture Mobilization in Repeated Mining of Multiple Coal Seams
Li, S. G. (Xi' an University of Science and Technology) | Ding, Y. (Xi' an University of Science and Technology) | An, Z. F. (Xi' an University of Science and Technology) | Li, H. T. (Xi' an University of Science and Technology) | Wei, X. W. (Xi' an University of Science and Technology)
ABSTRACT: Under the conditions of repeated mining in multiple coal seams, overlying strata experience repeated pressure relief, and the fracture paths are different from that formed in single coal seam mining. The movement of overlying strata, the fracture distribution and evolution, and the shape were investigated by physical tests and theoretic analysis. The results demonstrate that a mobilized elliptic parabolic zone would be formed if the bed-separated fissures and broken fissures are connected in the process of the overlying strata movement. Compacted area gives shrinkage effect with subareas further developing, and fracture of the overlying strata undergoes five stages, i.e. fracture initiation, expansion, compaction, expansion again and compaction again. Equations on voids and permeability in overlying caved rock, residual expansion coefficient, gob depth and the strata movement were established when composite gob becomes basically stable, which can be used to analysis the expanding characteristics of strata and the gap seepage characteristics of composite gob under the condition of repeated mining. At last, a mathematical model of the elliptic parabolic zone in overlying strata is derived, which provides a theoretical basis for determining the location of drilling hole for gas extraction. 1 INTRODUCTION Cracks in coal seam and rocks are the main channel of infiltration and fluid migration caused by overlying strata regularly cave, rupture and sink with the mining face advance (Qian & Miao 1996). Bai (1990) and Palchik V (2003) agree that there exist three different mobile belt above longwall mining gobs (caving zone, fracture zone, bending subsidence zone); Liu (1981), Qian (1983) established theoretical system of "Horizontal Three Area" and "Vertical Three Regions" on the basis of overburden failure and conductivity fracture distribution characteristics. Through experimental and theoretical research. Qian (1998 & 1997) put forward the theory of "O" ring. Yuan (2004 & 2008) put forward the concept of "roof annular crack circle". Lin (2007) called it a "recurrent" ringand and Li (1990 & 2000 & 2011) described it as "mining fissure elliptic paraboloid zone" and covered "mining fissure rounded rectangle ladder". Xie (2008) described it as an "arch" cap. The above researches reveal the evolution law of fracture zone in single coal seam mining, and form a more completely theoretical system which is playing an important role in guiding simultaneous extracting of coal and methane.
- Research Report > New Finding (0.34)
- Research Report > Experimental Study (0.34)