An experimental study on fracture evolution mechanism of a non-persistent jointed rock mass with various anchorage effects by DSCM, AE and X-ray CT observations

Bolt shows the obvious anchorage effect on jointed rock mass and has become an irreplaceable reinforcement method in all kinds of rock engineering. The influence of bolt support structure on the fracture evolution behavior of rock is an important source of reinforcement effect. Therefore in this research, a series of experiments are conducted to reveal the influence of anchorage method on the fracture evolution mechanism of a non-persistent jointed rock mass. Firstly, the relations between AE and the evolution of the strain field of non- persistent jointed rock specimen are constructed, which illustrates a distinct effect of the joint angle and the anchorage method on the AE characteristics and the evolution of strain field. And then, the effect of the joint angle and the pre-tightening force on internal surface cracks and three-dimensional fracture modes obtained by X-ray CT observation is analyzed in detail. The results demonstrate that for anchorage specimens with smaller joint angles, tensile wing cracks are usually dominated; whereas for anchorage specimens with larger joint angles, tensile wing cracks are difficult to initiate and the shear cracks are usually dominated during the loading. For the same joint angle, the propagating path of cracks in the non-persistent jointed specimens can deflect more and the propagating length will decrease more with the increase of the pre-tightening force. Furthermore, the tensile cracks can transform the secondary shear cracks under higher pre-tightening force. Finally, the evolution of bolt axial force in the non-persistent anchorage jointed specimens is discussed in detail, which further reveals the effect mechanism of the joint angle and the pre-tightening force on the fracture characteristic of jointed rock mass.