Study On The Deformation And Damage Rules Of Gas-filled Coal Base On Meso-mechanical Experiments

Disaster prevention and control of coal and gas outburst is the major challenge of the world's coal mine production faced. Studying on the deformation and failure process of gas-filled coal from the meso-mechanics perspective is a new attempt to reveal the mechanics of coal and gas outburst and research the corresponding prevent and control measures. In this paper, the gas-filled coal as research object, the analysis of meso-structure and characteristics of gas occurrence of coal, and research and development of experimental system and test methods as a research-based, macro & meso-mechanical tests, theoretical analysis and numerical simulation as a means to reveal the test rules of macro & meso damage of coal under gas effect and establish the dynamic damage prediction and evaluation model and solid-gas coupling model of gas filled coal. The purpose of this paper is to lay a theoretical and technological foundation for in-depth study of mechanical behavior of gas-filled coal, investigate newly effective measures for prevention and control of coal and gas outburst disasters. Some progress has been made through these researches as follows:1) The characteristics of meso-structure and gas occurrence of outburst coal were investigated. We summarized the genesis, classification and micro-structural characteristics of outburst coal, and analyzed section properties of the pore's volume fractal dimension and self-similarity & scale invariance of the crack's fractal dimension. The test result of the deformation of coal during adsorption & desorption single-phase gas (CH4) was used for analysis the law of adsorption deformation, and established equation of expansion of the relationship between stress and gas pressure. Through the experimental investigation on the permeability of coal under different stress, different gas pressures, and complete stress-strain of coal, the rules of permeability of coal samples under different conditions and the corresponding penetration evolution equation was established.2) A meso-mechanical testing apparatus of gas-filled coal has been developed, which can be used to carry out meso-mechanical experiment for soft rock and coal under different loading conditions and different gas pressure. Compared with the current meso-mechanics apparatus,it has the following advantages. Firstly, three types of force state are provided including uniaxial compression, plane strain and triaxial compression (σ2 =σ3). Secondly,several measuring methods are offered,and the real-time observation of the micro-structural images and the collection of stress-strain and acoustic emission signals are realized during experimental process. Thirdly, it is gas-tight and exploding endurable, which makes it similar to actual testing environment. Fourthly, the structure is very simple,low-cost and high reliability. Preliminary test results of gas-filled coal is shown that the testing apparatus can provide a new and practical test method for solid-gas coupled experiments. According to the characteristics of meso-mechanical testing apparatus of gas-filled coal, the rock meso-image processing system was established. To deal with the problem of the complexity and low quality for the existing image processing methods in meso-mechanical experiments of rocks, a man-computer method for image processing was put forward on the basis of the LS-SVM and image segmentation.3) The meso-mechanical experimental investigation was preceded under different gas pressure and different confining pressures. We analyzed the evolution of the dynamic fracture and failure modes of the coal specimen. The results show that the micro-crack damage evolution of coal sample observing surface is a fractal process; the fractal dimension can be quantitatively expressed as changes of stress state caused by the damage evolution of coal sample. Application of relevant theories of rock fracture mechanics to analysis typical crack growth under the combined effect of external stress, swelling stress and pore pressure. The failure process of coal sample which contained a single crack and the typical multiple cracks were simulated with RFPA numerical simulation software, and the fracture evolutionary process were obtained, and also had discussed the role of gas in the failure process of coal specimen.4) Based on acoustic emission experiments of the coal loading process, the comparative study of macro-mechanics and meso-mechanics were conducted. We analysis the rules of variations and correlation of AE parameters, frequency characteristics, fractal and chaos characteristics during the damage process of gas-filled coal. On these base, the comprehensive estimate and forecast model of dynamic damage was established with fuzzy comprehensive evaluation. The results of dynamic estimate of coal damage process are agreed well with variation of stress-strain.5) A meso-statistical damage constitutive model has been presented base on Weibull theory and Mohr-Coulomb rule using the method of damage meso-mechanical, which take into account the characteristics of solid-gas coupling of gas-filled coal. There are three types of methods of solving model parameters which have been proposed: regression solutions of model parameters, the method based on AE signal and fractal dimension of destroy surface. Considering the coupling effect ion of the stress field, seepage field and concentration field, we established a solid-gas coupling seepage model of gas-filled coal which based on the diffuse equation and seepage equation of gas transport, the effective stress equation and stress-permeability evolvement equation, and analyzed the definite conditions.6) The meso-mechanical analysis methodology for increasing permeability of the low-permeability coal seam was proposed through combining the solid-gas coupled micro-mechanical analysis method of the coal and project field. Application of this method to test micro-structures of original and after the pre-split blasting coal, the results show that the deep-hole controlled pre-split blasting improved the gas permeability of coal seam. We have proposed a forecasting and forewarning model for methane hazard based on the least square support vector (LS-SVM) multi-classifier and regression machine. The results obtained by LS-SVM regression show that the forecasting has a high precision, and forewarning results are credible. Therefore, it is an effective model building method for continuous prediction of methane concentration and hazard forewarning in working face.