Investigation of the macro–meso failure mechanism for soil–rock mixture under splitting loading using real-time ultrasonic measurement and 3-D laser scanning

Abstract

In this paper, real-time ultrasonic tests and post-test three-dimensional (3-D) laser scanning were performed to investigate the macroscopic and mesoscopic failure mechanism of soil and rock mixture (SRM) under the splitting loading, using a specially self-developed radial-splitting clamp for splitting strength testing. Artificial SRM specimens with roughly the same void ratio were produced with rock block percentage (RBP) of 20, 30, 40 and 50%, respectively. The fracturing evolution was discussed by analysing variation of ultrasonic pulse velocity (UPV) during splitting loading. Macroscopic failure morphology descriptions combined with mesoscopic 3-D laser scanning techniques were both used to reveal the internal failure mechanism. The results showed that splitting tensile strength of SRMs decreased with increasing RBP. UPV decreases monotonously with increasing splitting stress, and it follows power function with good correlation; the variation of splitting stress can be well reflected by the UPV during deformation. In addition, through the cracking evolution analysis using an index of total crack width defined by UPV, two distinct stages for crack propagation were first found. What is more, tension failure and tension-shear mixed failure modes coexisted for SRMs; the chaotic distribution of the rock blocks controlled the tortuosity of the failure surfaces. The fracture surfaces were forced to negotiate around rock blocks tortuously owing to the interactions between rock blocks and soil matrix, and the tortuous degree became severe with increasing RBP.