Size effect of holes in rock-like materials containing flaws on failure behaviors and fracture characteristics

Abstract Soft rock widely exists in nature with multi-crack low strength due to large pores, poor cementation, like mudstone, shale. At the same time, the influence of geological structure movement, the formations of various defects were formed in soft rock, such as cracks, cavities and so on. Due to the difficulty of sampling, rubber mortar is used to simulate the failure mechanism and fracture evolution of soft rock containing holes. Rubber mortar is a material similar to soft rock with low strength formed by partially replacing sand with rubber particles. In order to evaluate the failure behavior of soft rock with multiple cracks, rubber mortar with different diameters holes and cracks was prefabricated. Uniaxial compression test and DIC (digital image correlation) technique were used to reveal the failure mechanism and process. The results show that diameters of holes is small, wing cracks initiated the tip of cracks and with diameters increasing, initiation cracks developed to holes until only to start holes. Next, failure modes have one type: direct coalescence. Finally, Superposition principle and elastic-plastic fracture mechanics are used to analyze this failure mechanism for local stress to cause the damage. In sum, the experiment has uncovered successfully mesoscopic failure laws and macroscopic fracture mechanism of soft rock containing holes and fissures. The conclusions can be provided the references to design, construction and maintenance of deep tunnel engineering.