【作者】 刘延保；

【导师】 曹树刚；

【作者基本信息】 重庆大学 ， 采矿工程， 2009， 博士

【摘要】 煤与瓦斯突出灾害防治是世界各国煤矿生产中面临的重大难题。从细观力学试验出发,研究含瓦斯煤体的微细观变形及破坏过程是揭示煤与瓦斯突出机理,探索相应防治措施新的尝试。本文以含瓦斯煤体为研究对象,以微细观结构和瓦斯赋存特性分析、实验系统和试验方法的研发为基础,以宏细观力学试验、理论分析和数值模拟为手段,揭示瓦斯作用下煤体宏-细观损伤的试验规律,建立含瓦斯煤体的动态损伤预测评价模型和固-气耦合模型,为进一步全面地研究含瓦斯煤体力学行为,探讨新的有效防治煤与瓦斯突出灾害的技术途径奠定理论和技术基础。通过本文研究,在以下几方面取得一些进展:1)进行了突出煤体的微细观结构特征及瓦斯赋存特性研究。总结了突出煤体孔隙、裂隙的成因、分类及微细观结构特征,分析了突出煤样孔隙体积分形维数的分段性特征以及裂隙分形维数的自相似性与标度不变性。利用煤体吸附、解吸瓦斯(单相气体CH4)过程中变形的试验结果,分析了煤体的吸附变形规律,建立了煤体变形、膨胀应力与瓦斯压力的关系方程。通过不同地应力、不同瓦斯压力以及全应力-应变中的煤体渗透率变化规律的试验研究,分析了煤样渗透率变化规律,建立了相应的渗透率演化方程。2)自行研制了含瓦斯煤岩细观力学实验系统。该系统可进行不同受力状态,不同瓦斯压力条件下软弱煤岩的细观力学试验,与现有的细观试验装置相比,具有以下特点:可提供单轴、平面应变、三轴(σ2 =σ3)三种受力状态;试验测试方法多样化,可进行试验过程中的实时显微图像观测和应力–应变、声发射信号的采集;具有良好的气密性和耐爆性,创造具有瓦斯的试验环境,使煤与瓦斯突出机制的试验研究更加接近矿山实际;装置的结构简单,成本低,系统可靠性高。初步的试验结果表明,该试验装置为固–气耦合条件下的相关试验研究提供新的测试手段,具有较大实用价值。根据含瓦斯煤岩细观力学实验系统的特点,建立了岩石细观图像处理系统;为了解决岩石细观力学试验中图像处理过程复杂、质量不高及操作效率低等问题,将LS-SVM的分类方法与数字图像处理的阈值分割法相结合,提出了人机结合的岩石细观结构图像系统分析方法。3)开展了不同瓦斯压力下、不同围压下的突出煤体细观力学试验研究。分析了煤样的动态破裂演化过程以及破坏形式,结果表明,煤样观测面的微裂纹损伤演化是一个分形过程,分形维数可以定量地表示随应力状态的变化引起煤样损伤破裂的演化规律。应用岩石断裂力学的相关理论对在外部应力、孔隙压力和膨胀应力三者共同作用下的典型裂隙的开裂、扩展条件进行分析,并结合RFPA数值模拟软件对含单一裂纹以及典型裂纹系的煤样破裂过程进行模拟,得到了各条件下煤样破裂的演化过程,讨论了瓦斯在煤体破坏过程中的作用。4)进行了基于煤样受载过程的声发射试验的宏细观力学的对比分析研究。对含瓦斯煤样损伤破坏过程中声发射参数变化规律、声发射参数的关联性、声发射的频谱特征及分形和混沌特征进行分析。在此基础上,应用模糊数学综合评价方法,基于声发射信息建立了煤岩动态损伤综合预测评价模型,对煤体损伤破坏过程进行动态评价,研究结果与应力-应变变化规律基本一致。5)采用细观损伤力学的研究方法,充分考虑含瓦斯煤岩固-气耦合特点,以Weibull理论框架为基础,基于Mohr-Coulomb准则建立含瓦斯煤岩细观统计损伤本构模型,提出了模型参数的回归解、基于声发射信号的求解方法和基于岩石表面断裂过程分形维数等三种模型参数求解方法。综合考虑应力场、渗流场和浓度场的耦合作用,在瓦斯运移过程中的扩散方程和渗流方程、含瓦斯煤体的有效应力方程以及应力-渗透率演化方程的基础上,建立了含瓦斯煤岩固-气耦合渗流模型,并分析了模型的定解条件。6)将煤岩固-气耦合细观力学分析方法与工程现场相结合,提出了低渗透煤层增透途径的细观力学分析方法。应用该方法对深孔控制预裂爆破增透前后的煤体作了微细观结构测试和现场效果分析,表明深孔控制预裂爆破明显地改善了煤层的透气性。基于最小二乘支持向量机的回归预测和分类方法,建立了采煤工作面瓦斯危险性预测预警模型,应用实例证明该模型预测结果精度高,预警结果可信度高,可作为采煤工作面瓦斯浓度连续预测与危险性预警的有效建模手段。更多还原

【Abstract】 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.更多还原