采动影响下煤岩力学特性及瓦斯运移规律研究
发布时间：2018-03-31 17:32
本文选题：含瓦斯煤岩 切入点：采动 出处：《重庆大学》2014年博士论文
【摘要】：随着煤矿开采深度的增加，地应力、瓦斯压力增大，煤层的渗透性降低，瓦斯灾害事故频繁发生。由于采动的影响，煤岩应力发生重新分布，经历了加载和卸载共同作用的复杂应力途径。以往多采用常规的加载方式对煤岩的力学和渗透特性进行研究，这与实际情况有较大的差异。为此，本文采用试验研究、理论分析、数值模拟等相结合的方法，利用自行研制的“含瓦斯煤热流固耦合三轴伺服渗流实验装置”，对常规加载条件和不同加卸载条件下含瓦斯煤的力学特性和渗透规律进行试验研究，揭示不同加卸载条件下含瓦斯煤的变形模量、泊松比、强度以及渗透特性等变化规律；研制了“多场多相耦合下多孔介质压裂-渗流实验系统”并进行了煤岩不同开采条件下力学特性及渗透率变化规律的试验研究；利用“多场耦合煤矿动力灾害大型模拟试验系统”对真三轴应力状态下大尺度煤岩在常规加载及不同开采条件下的力学及渗流特性进行研究；建立了常规加载及不同加卸载条件下含瓦斯煤的有效应力计算公式及渗透率与有效应力关系的公式；采用数值计算的方法，对煤层瓦斯在采动影响条件下工作面前方和采空区上方采动裂隙场中瓦斯运移规律进行数值模拟分析。本文主要研究成果如下： ①采动应力影响下煤岩的应力路径表现为轴向应力加载和围压卸载的共同作用。含瓦斯煤的承载强度与不同的加卸载条件有如下关系：加卸载煤样的承载强度随初始轴力的升高呈指数关系降低，随围压卸载速度的增加呈指数函数关系降低，，随初始围压的升高呈指数关系降低，随瓦斯压力的升高呈线性关系降低。变形模量随轴向应变的增加均呈先迅速减小然后缓慢减小直至破坏后保持基本稳定的趋势；不同加卸载条件下含瓦斯煤的泊松比均表现出随着轴向应变的增加先逐渐减小后迅速增加最后基本保持稳定。 ②常规加载与加卸载条件下煤样渗透率与应变的关系在屈服前规律有所不同，屈服前常规加载渗透率与应变呈二次曲线关系减小；而加卸载渗透率随应变首先呈线性关系增加然后呈二次曲线关系减小。煤样屈服后两种条件下渗透率与应变的关系规律基本相同，即呈指数关系增大，且与轴向应变呈正指数关系增大，与径向应变和体积应变呈负指数关系增大。 ③三轴加载及加卸载条件下含瓦斯煤变形破坏过程中弹性应变能的变化趋势与轴向应力的变化趋势相对应。围压卸载过程中，含瓦斯煤单元耗散能随着卸载位置轴向压力的增加而增加，且其占单元总能量增加量的比例增大。 ④自行研制了“多场多相耦合下多孔介质压裂 渗流实验系统”，并利用该系统进行了常规加载及不同开采条件下煤岩的试验研究。常规加载条件含瓦斯煤的峰值强度远远大于开采条件下含瓦斯煤的峰值强度，无煤柱开采、放顶煤开采、保护层开采三种开采条件下含瓦斯煤及不含瓦斯煤的峰值强度依次降低。 ⑤真三轴应力状态下大尺度煤岩渗透率变化曲线与体积应变变化曲线有较好的对应关系，渗透率均首先随着体积应变的增加而减小，然后随着体积应变的减小而有不同程度的增加。无煤柱开采、放顶煤开采、保护层开采煤岩渗透率在减小阶段其减小量依次减小，渗透率在增加阶段其增加量逐渐增加。一定瓦斯压力范围内，瓦斯压力越大，大尺度煤岩渗透率减小量越小，渗透率增加量增加。 ⑥考虑瓦斯力学作用和瓦斯吸附作用两个方面对有效应力系数的影响，建立了单调加载及加卸载条件下原煤的有效应力计算公式及渗透率与有效应力关系的公式。含瓦斯煤的有效应力系数随着围压的增加而线性减小，含瓦斯煤的有效应力系数随着瓦斯压力的增加而线性增加，加卸载条件下的有效应力系数小于单调加载条件下的有效应力系数。 ⑦基于采动影响下煤层瓦斯运移的数学模型，利用UDEC软件模拟开采过程中裂隙场的演化形态，随着工作面的不断推进，采空区上方上覆岩层形成采动裂隙梯形台，并进行了煤层瓦斯在采动裂隙场中瓦斯运移动态演化规律的COMSOL数值模拟研究，采动裂隙场中的离层裂隙和竖向破断裂隙具有瓦斯流动导向性。 ⑧利用COMSOL软件模拟分析工作面前方三种开采条件下煤层瓦斯渗透率变化规律与支承压力分布规律，两者有较好的对应关系。随着工作面推进距离的增加，三种开采条件下煤层支承压力对应的应力集中系数增加，且增加的趋势逐渐变缓；当工作面推进距离相同时，无煤柱开采、放顶煤开采、保护层开采三种开采条件下应力集中系数依次降低。
[Abstract]:With the increase of the mining depth of coal mine , the stress and gas pressure increase , the permeability of the coal seam decreases , and the gas disaster accidents happen frequently . Due to the influence of mining , the coal - rock stress is redistributed . The mechanical properties and permeability of the coal - bearing coal under different loading conditions are studied , and the variation law of deformation modulus , Poisson ' s ratio , strength and permeability of gas - containing coal under different loading conditions are revealed .
In this paper , a multi - field multi - phase coupled porous medium fracturing - seepage experimental system was developed and the mechanical properties and permeability variation law of different mining conditions were studied .
The mechanical and seepage characteristics of large scale coal rock under normal loading and different mining conditions are studied by using the " Multi - field Coupled Coal Mine Dynamic Disaster Large Scale Simulation Test System " .
The formulas for calculating the effective stress and the relationship between permeability and effective stress of gas - containing coal under normal loading and different loading conditions are established .
The numerical simulation of the gas migration law of coal seam gas under the influence of mining operation is carried out by numerical simulation . The main research results are as follows :
The stress path of coal rock under the influence of mining stress is the joint action of axial stress loading and confining pressure unloading . The bearing strength of coal containing gas decreases exponentially with the increase of initial axial force .
The Poisson ' s ratio of gas - containing coal under different loading conditions shows that the increase of axial strain increases first and then increases rapidly .
( 2 ) The relationship between the coal sample permeability and strain under normal loading and loading conditions is different before the yield , and the relationship between the conventional loading permeability and strain before yielding is reduced ;
The relationship between permeability and strain is basically the same , that is , exponential relationship increases , and the relationship with axial strain increases with negative exponential relationship with radial strain and volumetric strain .
( 3 ) The change tendency of elastic strain energy in the process of triaxial loading and loading and unloading is corresponding to the changing tendency of axial stress . During confining pressure unloading , the dissipation energy of gas - containing coal unit increases with increasing axial pressure of unloading position , and the proportion of total energy increment of the unit increases .
鈶ｈ嚜琛岀爺鍒朵簡鈥滃鍦哄鐩歌
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