Abstract

A triaxial unloading mechanical test is conducted on sandstone considering different initial confining pressures and unloading rates under the effect of hydraulic coupling. The energy evolution of sandstone unloading failure is studied, and the influences of the initial confining pressure and unloading rate on the deformation characteristics and permeability evolution of sandstone are discussed. It is found that the initial confining pressure and unloading rate have a significant impact on the axial and radial strains of the sandstone, and the radial deformation is more sensitive to the unloading process. The energy dissipation of the sandstone sample increases with the increase of the confining pressure and is nonlinearly correlated to the unloading time. The permeability during the unloading deformation of the sandstone decreases with the increase in the initial confining pressure, indicating that the initial confining pressure of unloading has an inhibitory effect on the permeability of the sandstone. The permeability decreases with the increase in unloading rate, indicating that the faster the increase in the unloading rate, the greater the dissipated instantaneous elastic energy, which is accumulated and released during failure. The higher the degree of fracture in the sample, the larger the peak value of permeability.

摘要

在液力耦合作用下，考虑不同初始围压和卸荷速率，对砂岩进行了三轴卸荷力学试验。研究了砂岩卸荷破坏的能量演化，探讨了初始围压和卸荷速率对砂岩变形特征和渗透率演化的影响。发现初始围压和卸载速率对砂岩的轴向和径向应变有显着影响，径向变形对卸载过程更为敏感。砂岩样品的能量耗散随着围压的增加而增加，与卸载时间呈非线性相关。砂岩卸载变形过程中的渗透率随初始围压的增加而减小，表明卸载初始围压对砂岩渗透率具有抑制作用。渗透率随着卸载率的增加而降低，表明卸载率增加得越快，耗散的瞬时弹性能越大，在破坏过程中积累和释放。样品断裂程度越高，渗透率峰值越大。表明卸载速率增加得越快，耗散的瞬时弹性能越大，在失效过程中积累和释放。样品断裂程度越高，渗透率峰值越大。表明卸载速率增加得越快，耗散的瞬时弹性能越大，在失效过程中积累和释放。样品断裂程度越高，渗透率峰值越大。