饱水环境下致密砂岩的微裂纹损伤行为

发布时间：2018-09-19 14:58

【摘要】：岩石内部存在大量微裂纹,在外荷载作用下微裂纹扩展形成损伤发展,最终导致岩石材料破坏,微裂纹是岩石最重要的损伤机制。孔隙水会促使微裂纹扩展,建立损伤模型时需考虑孔隙水压对损伤发展的影响。利用MTS815岩石力学试验系统,开展了致密砂岩的单轴压缩实验和多种围压下的三轴压缩实验以及多种孔隙水压下的水渗流全应力应变实验。实验结果表明砂岩在自然状态下的抗压强度高于饱水状态下的抗压强度,而其有效弹性模量没有明显的差异;围压会显著提高砂岩试件的抗压强度,二者之间存在线性相关性,饱水试件的抗压强度随着孔隙水压的增大而显著降低。考虑孔隙水压对微裂纹演化行为的影响,引入能量平衡原理描述微裂纹扩展,分别研究微裂纹张开、摩擦滑移、面内扩展、偏折扩展以及微裂纹汇合对岩石变形的影响,建立了饱水砂岩的统计损伤模型。基于该理论模型编写了计算程序,对不同孔隙水压下砂岩的三轴压缩实验进行了数值计算,其计算结果与实验结果基本吻合。计算表明该细观损伤模型也适用于含瓦斯煤岩。研究了微裂纹相互作用对岩石变形的影响,有限元计算结果表明当微裂纹平均间距参数低于2时微裂纹相互作用对微裂纹变形有明显的影响。基于Mori-Tanaka方法,建立了能考虑椭圆形微裂纹之间相互作用效果和微裂纹扩展的细观损伤模型,理论计算结果表明,当微裂纹间距参数小于2时应当采用考虑微裂纹相互作用的理论模型,而微裂纹间距参数大于3时则无需考虑微裂纹相互作用对岩石变形的影响。
[Abstract]:There are a large number of microcracks in the rock, and the microcracks under external load form damage and development, which leads to the failure of rock materials. Microcracks are the most important damage mechanism of rock. Pore water can promote microcrack propagation, and the influence of pore water pressure on damage development should be taken into account in establishing damage model. Using MTS815 rock mechanics test system, uniaxial compression experiments of tight sandstone, triaxial compression experiments under various confining pressures and full stress strain experiments of water seepage under various pore water pressures have been carried out. The experimental results show that the compressive strength of sandstone in natural state is higher than that in saturated state, but there is no obvious difference in effective modulus of elasticity, the confining pressure can significantly increase the compressive strength of sandstone specimen, and there is a linear correlation between them. The compressive strength of saturated specimen decreases significantly with the increase of pore water pressure. Considering the influence of pore water pressure on the evolution behavior of microcracks, the energy balance principle is introduced to describe the microcrack propagation. The effects of microcrack opening, friction slip, in-plane propagation, deflection propagation and micro-crack convergence on rock deformation are studied, respectively. The statistical damage model of saturated sandstone is established. Based on the theoretical model, a computer program is developed to calculate the triaxial compression experiments of sandstone under different pore water pressures. The calculated results are in good agreement with the experimental results. The calculation shows that the meso-damage model is also suitable for gas-bearing coal rocks. The effect of microcrack interaction on rock deformation is studied. The finite element calculation results show that the microcrack interaction has a significant effect on the microcrack deformation when the average distance parameter of microcrack is less than 2. Based on the Mori-Tanaka method, a meso-damage model considering the interaction effect between elliptical microcracks and the propagation of microcracks is established. The theoretical results show that, When the parameter of microcrack spacing is less than 2, a theoretical model should be adopted to consider the microcrack interaction, but the effect of microcrack interaction on rock deformation should not be considered if the microcrack spacing parameter is greater than 3.
【学位授予单位】：湖南科技大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TU45

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