水-力耦合条件下砂岩声发射和能量耗散的颗粒流模拟

对砂岩进行水-力耦合三轴试验和声发射实时监测，得到水-力耦合作用下砂岩应力-应变曲线和声发射数据。根据试验条件和结果建立离散元颗粒流的水-力耦合双轴模型，研究砂岩声发射和能量演化规律。通过定义耗散能，用耗散能增量较好地诠释了声发射的发展规律。利用微破裂源可追踪声发射局域源，得到水-力耦合条件下的声发射空间分布和裂纹类型。研究表明：（1）孔隙水压力对颗粒的拖拽力削弱了颗粒间的平均接触力，从而降低了砂岩整体强度。（2）孔隙水压力反映出对弹性应变能有一定程度的反复“贮存和清空”作用，造成声发射能量相对离散和峰后的应力波动。（3）渗透压的存在提升了总输入能的耗散效率，降低了总输入能和弹性应变能，须综合考虑总输入能（弹性应变能）和耗散效率才能确定累计耗散能。（4）裂纹分布表现为可能出现与主剪切带呈一定夹角的伴生裂隙带，且受水-力梯度影响，进水端比出水端更密集。（5）张拉裂纹与剪切裂纹的比值于峰值强度处显著增加，峰后趋于稳定。

Acoustic emission of sandstone with hydro-mechanical coupling and PFC-based modelling of energy dissipation

Hydro-mechanical coupling triaxial tests and acoustic emission monitoring experiments are performed on a sandstone, and the stress-strain relationship and acoustic emission (AE) data of sandstone are obtained under hydro-mechanical coupling conditions. Based on the experimental conditions and results, a HM coupling biaxial model is developed using the 2-dimensional particle flow code (PFC2D) to study the AE characteristics and energy dissipation of sandstone. By its very definition, the incremental dissipation energy can be effectively used to interpret the evolution of AE characteristics. AE source can be traced according to micro cracks, and then the spatial distribution of AE signals and the types of the micro cracks are determined. The results show that: 1) The average contact force between particles is weakened by the dragging force induced by pore water pressure so that the overall strength of sandstone is reduced. 2) The pore water pressure variation reflects the repeated “storage and depletion” nature of the elastic strain energy, which leads to the relatively scattering of AE energy and stress fluctuation after its peak value. 3) The existence of the osmotic pressure promotes the dissipation efficiency of the total input energy, while lessening the total input energy and elastic strain energy. It is necessary to consider the total input energy (elastic strain energy) and dissipation efficiency in determining the total dissipation energy. 4) Crack distribution shows a possible occurrence of an associated crack zone, which is at a certain angel to the main shear zone. Influenced by the hydraulic gradient, the cracks become denser in inlet for water than outlet. 5) The ratio of the tensile crack number to the shear crack number increases sharply at the peak stress then tends to be constant afterwards.