Experimental study on the failure characteristics of high stress unloading rock mass induced by disturbance

In order to study the failure characteristics of single sided unloading rock mass with different intermediate principal stress induced by disturbance,a true triaxial disturbance unloading test system and an acoustic emission monitoring system were used to carry out different intermediate principal stress unloading experiments and unloading disturbance experiments.The influence of principal stress on the strength characteristics,evolution law,and fracture mode of single sided unloaded rock was analyzed.Furthermore,the mechanical properties of unloaded rock after disturbance in σ2 direction were analyzed.The results show that with the increase of the intermediate principal stress,the stability and peak strength of the unloaded rock are enhanced,but a larger one will gradually weaken the rock bearing capacity.With the increase of stress,the cracking mode of unloading rock gradually changes from tension shear failure to tension fracturing failure.Besides,at σ2≤30 MPa,the acoustic emission of rock failure experiences calm and continues to appear accompanied by a small sudden increase and a steep rise,continuous low peak,and large sudden increase of damage.After σ2＞30 MPa,the signal experiences calm,continuous appearance,multiple low peaks,and continuous rising damage.Moreover,the failure of unloaded rocks after different types of disturbances is significantly different.After the medium frequency and medium amplitude disturbances,the unloading surface forms obvious V shaped failure pits,and the fractal dimension of the debris is the largest.Therefore,the mid frequency and mid amplitude disturbance not only accelerates the nucleation of small cracks near the unloading surface with small constraining force,but also accelerates the connection between large cracks far away from the unloading surface.The damage of bearing capacity is medium frequency medium amplitude> high frequency low amplitude> low frequency high amplitude.During engineering construction,σ2 cannot be simply increased to enhance the surrounding rock bearing capacity.Besides,it must also be considered comprehensively that the increase of σ2 will increase the severity of unloading rock mass failure.To reduce the disturbance of surrounding rock caused by blasting and machinery,the frequency or amplitude of disturbance cannot be changed alone.