不同围压下砂岩能量变化试验研究

Experimental study on energy features of sandstone under different confining pressures

为了解周期载荷对岩石类材料力学性能的影响,利用MTS 815程控伺服岩石刚性试验系统,对砂岩进行不同围压下的加卸载试验,研究不同围压下的加卸载过程及砂岩变形特征的能量变化情况。分析表明:1)岩石在不同围压下的加卸载过程中,会形成一个开口向下的"尖叶状"滞回环,且随围压增大,滞后回线沿轴向应变增大的方向移动,且不可逆;2)根据砂岩弹性能量指数的变化,一定程度上揭示岩石在压密阶段的能量变化过程;3)静态三轴实验状态下,砂岩的平均能量指数与围压呈现一定的函数关系;4)总体上,砂岩的弹性能量指数随围压的增加而逐渐减小。这表明轴向压力作用下砂岩随围压的增加,吸收外界施加能量的能力逐渐变弱。

In practical constructional engineering, the mechanical properties of rock materials are extensively influenced by cyclic loading,by which the stability of the engineering is also affected in certain degree. Taking advantage of MTS 815 programmable servo rock stiffness testing system,a loading and unloading test on sandstone under different confining pressures is conducted in this paper to study its deformation behavior and energy variation during the test. Test results are as follows:1)Rock will form a pointed-leaf shaped hysteretic loop with open side down during loading and unloading process, meanwhile, the loop moves irreversibly towards the direction of increasing axial strain as with the growth of confining pressure. 2)To some extent, the energy changing process of rock in compaction stage has been uncovered as with the variation of elastic energy index of sandstone. 3)A certain function relationship between the average energy index of sandstone and confining pressure is manifested in the state of static triaxial test. 4)Generally,the elastic energy index of sandstone decreases with the increase of confining pressure. It shows that the ability of sandstone to absorb external energy is gradually weakened as with the increase of confining pressure under the effect of axial compressive force.