Study of the effect of loading rates on crack propagation velocity and rock fracture toughness using cracked tunnel specimens

Abstract

In the process of tunnel blasting excavation, radial cracks could be induced. To investigate the effect of loading rates on crack propagation velocity and rock initiation toughness, a new cracked tunnel specimen was proposed in this paper, and drop weight impact experiments were conducted. The crack propagation velocity and crack initiation time were measured by using crack propagation gauges (CPGs), and the measuring results were applied in the determination of initiation toughness. In order to validate the effectiveness of the cracked tunnel specimens and to predict the test results, finite difference numerical models were established by using AUTODYN code. The simulation results of crack propagation speeds and delayed fracture time generally agree with the experimental results, and crack arrest phenomena occur during crack propagation. The dynamic stress intensity factors (SIFs) were calculated by using ABAQUS code, and the initiation toughness under different loading rates was obtained by using experimental-numerical method. The studying results show that crack propagation speeds and initiation toughness increase with loading rates, but as the loading rate is larger than a certain value, the crack speeds tend toward a stable value; Delayed fracture time decreases with the increase of loading rates, and as the loading rate is larger than a certain value, it tends toward a stable value.