循环加、卸载速率对砂岩变形和渗透特性的影响

通过煤岩热流固耦合试验系统(THM-2)对砂岩进行循环加、卸载试验,研究加、卸载速率对其变形和渗透特性的影响.结果表明:初始循环时,岩石的轴向变形量△ε1较大,随着循环试验的进行,△ε1趋于稳定,受卸载速率v2的影响较小.加载变形模量和卸载变形模量均逐渐上升,随着循环次数的增加,上升速度逐渐变缓;同一循环内,卸载变形模量大于加载变形模量,且随着加、卸载的进行,差值逐渐减小.加载阶段和卸载阶段渗透率变化量的差值随着循环次数的增加逐渐减小;从第5次循环开始,渗透率曲线呈“∞”形,渗透率演化规律可以用轴向应变的变化特点表征,轴向应变的变化量△εi1受到卸载速率vi2和应力加载上限σimax的综合作用,二者对应变在卸载初期起到积极的促进作用,三者之间的相互关系可用幂函数表达.

Deformation and permeability of sandstone at different cycling loading-unloading rates

In order to research the effect of cycling loading and unloading rates on the deformation and permeability of sandstone,cycling loading and unloading tests were performed with a self-made thermal-hydrological-mechanical coupling test system for gas-infiltrated coal and rock.The results show that the axial deformation of sandstone △εt is larger in the initial cycle and tends to be stable with cycling,but the influence of unloading rate is minimal.The loading deformation modulus and unloading deformation modulus both increase and the rising speed becomes slow with the increase of the number of cycles.In the same cycle,the unloading deformation modulus is bigger than the loading deformation modulus,and their difference gradually decreases with the test proceeding.Meanwhile,the difference of permeability variations in loading and unloading phases decreases with the increasing of unloading rate.Starting from the fifth cycle,the shape of permeability curves is "∞ ".The evolution rule of permeability can be characterized by using the change regularity of axial strain.The variation of axial strain △εi1 is influenced by unloading rate vi2 and loading stressσmax,which both promote the development of strain.The relationship of them can be characterized with a power function.