An experimental study on anchorage strength and deformation behavior of large-scale jointed rock mass

Abstract

By adopting the similarity theory, a large-scale model experiment system (the dimension of specimen is 500×500×480mm) is firstly self-developed, which not only has a good loading, restraint and measuring function, but also satisfy the strength and stiffness of the large-scale experiment. In the experimental system, optical fiber dynamometric bolt based on Bragg grating is adopted to measure internal force of anchorage jointed rock mass with a high precision. Secondly, the molds for the large-scale jointed model specimen are fabricated, and the materials (including the rock-like material and the supporting material) are all developed successfully. And then, the anchoring strength behavior of large-scale jointed rock mass is analyzed in detail. The experimental results shows that the anchoring strength of the large-scale rock mass with different joint angles of 30°, 45°, and 60° are greater than that of jointed rock mass without any bolts, but being dependent to joint angle. The peak strength increases nonlinearly with the increase of bolt number for the same joint angle. The anchoring mechanism of peak strength strengthening is explained by the following three parts: the peak strength of jointed rock mass without any bolts under the uniaxial stress, the peak strength contributed by the initial equivalent restraint stress, and the peak strength contributed by the deformation equivalent restraint stress. With the increase of the initial equivalent restraint stress, the peak strength of anchorage jointed rock mass will increase linearly. Moreover when the joint angle is bigger, the contribution of initial equivalent restraint stress on the peak strength is larger. In the end, the effect of bolt number and joint angle on the deformation and dilatancy behavior of jointed rock mass is analyzed. In general, the elastic modulus increases nonlinearly with the increase of bolt number for the same joint angle. For anchorage rock mass with the same joint angle, the value of the negative ratio of circumferential strain to axial strain at the peak stress increases gradually with the increase of bolt number; but for anchorage rock mass with the same bolt number, the value of the negative ratio of circumferential strain to axial strain at the peak stress is dependent to the joint angle. The dilatancy stress of large-scale jointed rock mass increases nonlinearly with the bolt number but increases linearly with the equivalent restraint stress.