The Theory Of Surrounding Rock Control And The Assessment Research Of Recoverability In Thick Residual Coal Seam Remining Stope

Our country is a coal production and consumption country. Coal resource accounted for more than 70% in the proportion of primary energy consumption structure, and this consumption structure can not be changed in quite a long time. China is a rich coal, oil-poor, less gas country, the coal resources account for 11% of total world reserves, but China’s per capital share of the coal resource less than half the world average, the shortage of resources will directly affect the future development and survive of China. However, due to lack technical equipment and process etc, thick seam mining technology include gateway and pillar,gateway top coal caving(fall-high), residual and pillar etc mining method before the nineties of the last century, caused serious waste in mining. With the development of mining technology and mining theory, these residues untapped coal resources "residual coal" has possible to re-use。Comprehensive mechanized longwall cover caving coal mining method is the efficient method for remining residual coal resource. It has experienced decades of development and improvement, its mining technology, supporting equipment, mine pressure regulation and safety technical measures have been approached perfection. However, the effect from the legacy of the old mining abandoned area, abandoned lane, the roof caving breaking structure, the rock stress distribution and the deformation characteristics of caving mining face have obvious different with normal mining.Thus, this paper fully investigated the residues situation of thick seam mining in Shanxi Province, it summed up the residual mining loss situation and residual coal remining complex mining type, regard Sheng Hua residual coal 3101 coal mining working face as geological prototype, theoretical research, numerical simulation combined with similarity simulation method,and which made a systems research for the roof fracture, movement law of roof, and rock stress distribution of the residual nearly horizontal thick coal seam longwall mechanized cover caving coal mining. it provided a comprehensive assessment system of residual coal remining to evaluate the admissibility. The main contents and results as follows:(1) Based on the coal seam characteristics after the residual remining,there are four fundamental types include: vertical remining across coal pillar, horizontal remining across coal pillar, oblique remining across coal pillar and block remining across coal pillar.(2) Using two-dimensional plane, three-dimensional space and simulation experiments to study the structure characteristics and movement laws. The results show that: the major fracture characteristic of the residual remining coal stope is “pre-break”, the begin in the movement of the rock layer before the coal wall. The movement deformation curve represent significantly different volatility degrees in "wavy" subside basin, the transitional rock girder structure between overlying strata and irregular rock layer has been established after analyzed the results. This paper analysis the breaking location of the "key block " and instability mechanism in the perspective of mechanics. It determine the primary influence factors include the width of the abandon lane, the extreme dimension of the pillar and length of the suspension below the coal wall, and then build the relation between those factors(3) Using similar simulation and theoretical calculations to study the relationship among the distribution laws of stope abutment pressure, evolution rules and the effect between supports and surrounding rock. Based on the stability of coal pillar in front of the faces divides abutment pressure and its development process into three phases. The destabilization of coal pillars caused by stress superposition could result in dramatic changes of abutment pressure is one of the symbols. Through the result of similar simulation build the mechanical model between the support and the surrounding rock and determine a method to calculate the resistance of the support.(4) The mechanical model about the stability of the support has been established and make a research about the instability of the support.There is a classification based on the stability of hydraulic support which include pushing-collapsing type accident and pressure-collapsing type accident.Through research the instability mechanism of support, the results show that the main reason of the support instability is the pre-breaking roof in stope, the instability pillar ahead of the working face and the roof caving on the abandoned roadway.(5) Comprehensive support as the major method for controlling surrounding rock. Systematic study of the comprehensive technology measures to ensure surrounding rock control mechanism to protect. To control the surrounding rock of stope in the residual coal remining, we provide two methods: change the support system of the residual coal area to the roof; transfer the location of the stress concentration and decrease the factors of the stress concentration. Through the establishment of the mechanical model to analyze the effects of different control projects to support’s stability. The results show that applying the control projects like support abandoned roadway before mining, the presplitting roof by explosive and control the coal wall caving and the top-coal flaking could increase the stability greatly.(6) According to the theory of environmental resources and natural value, we propose evaluation method of residual coal remining. We build a prediction model to calculate the fracture structure of the roof. Using multivariate multilevel numerical method to present the residual coal mining safety admissibility evaluation system.The research results enlarge the control theory of the residual coal mining stope wall rock and evaluation system have practical significance and theoretical value to guide our residual coal remining practices and promote the efficient use of coal resources and coal sustainable development.