循环加卸载对岩体残余强度影响的试验研究

EXPERIMENTAL RESEARCH ON INFLUENCE OF CYCLIC LOADING AND UNLOADING ON ROCK MASS RESIDUAL STRENGTH

地下工程中,处于深部高地应力区的地下巷道、洞室、矿柱等的力学特性都与岩石破坏后的力学特性有密切联系,研究岩体残余强度及峰后力学特性对工程设计有着非常重要的意义。通过对处于残余强度状态岩样的循环加卸载试验,研究不同围压下(30,20,10,5和1MPa)、不同卸荷量(90%,70%,30%)造成的岩样残余强度变化规律,其中卸荷量为卸除荷载与相应围压下岩样残余强度的百分比。试验结果表明:不同围压、卸荷量条件下,岩样残余强度与循环次数的变化规律均可用指数函数很好地进行拟合,受初始条件影响不大;围压较低时(≤20MPa),同一围压下,卸荷量为70%时岩样残余强度的降低程度最大,其次是卸荷量为90%时;卸荷量为30%时,对残余强度造成的影响最小;当卸荷量相同时,围压越低,循环加卸载造成岩样残余强度降低程度越大,围压为1MPa时,残余强度最大可降低73%;围压较高时(>20MPa),由于围压的约束和压密作用,循环加卸载不会造成岩样残余强度的降低。

The mechanical properties of underground tunnel,cavern and pillar in deep high stress area are closely linked to the mechanical properties of rock after failure.Research on residual strength and post-peak mechanical properties of rock mass has very important significance for engineering design.Through cyclic loading and unloading experiments of failure rock mass,variation law of residual strength under different confining pressures（30,20,10,5 and 1 MPa） and different unloading degrees （90%,70%,30%） has been studied.The results show that the relationship between residual strength and cycle number can be fitted with the exponential function,no matter how the initial conditions are.When the confining pressure is relatively lower（≤20 MPa）,at the same confining pressure,the reduction degree of residual strength is the maximum at unloading degree of 70%,followed by unloading degree of 90%.On the other hand,the reduction degree of residual strength is the minimum at unloading degree of 30%.With the same amount of unloading degree,the lower the confining pressure is,the greater the reduction degree of residual strength is;under confining pressure of 1 MPa,the residual strength even may reduce by 73%.As confining pressure is large（20 MPa）,because of binding and compressive effect of the confining pressure,cyclic loading and unloading will not result in lower residual strength of rock samples.