(Poster session) Earth & Resources

[P008A] Study on effect of rock anisotropy on rock fracturing under various loading rates condition

○Kosuke Ichikawa^{1[Student presentation: Master’s course]}, Gyeongjo Min¹, Daisuke Fukuda¹, Sangho Cho², Satoru Kawasaki¹ (1. Hokkaido university, 2. Chengbuk national university)

Keywords:fracture toughness, Split Hopkinson Pressure Bar

Understanding the fracture behavior of rocks is essential for analyzing and predicting rock mechanics phenomena such as blasting, slope instability, and the long-term stability of underground structures. Fracture toughness is a key parameter for evaluating a material’s resistance to crack initiation and propagation. While Mode I and Mode II fracture toughness have been widely studied under quasi-static loading, their behavior under dynamic conditions remains poorly understood. Previous studies have reported strong loading-rate dependence in compressive and tensile strength, often accompanied by variations in fracture patterns. Based on these findings, it is anticipated that Mode I and Mode II fracture toughness may also exhibit significant rate sensitivity. Moreover, the influence of rock anisotropy on fracture propagation suggests it may affect the rate-dependent fracture behavior as well. In this study, Finite Element Method (FEM) simulations incorporating the J-integral were first conducted to evaluate geometry-related terms, considering specimen geometry and material anisotropy. Subsequently, Mode I and Mode II fracture toughness tests were carried out under a wide range of loading rates. Quasi-static loading was applied using a servo-controlled hydraulic system, and dynamic loading was implemented using a Split Hopkinson Pressure Bar (SHPB) , widely used for dynamic rock fracture testing in rock dynamics. While previous studies have often used mixed-mode fracture tests to investigate the loading-rate dependence of the Mode I to Mode II fracture toughness ratio, this study aims for a more ideal evaluation by conducting separate experiments for each fracture mode. In this sense, the Semi-Circular Notched Disk Bending (SNDB) and Short Core in Compression (SCC) methods were used for Mode I and Mode II, and it’s ratio respectively.The study examines the loading rate dependence of fracture toughness and crack initiation and propagation in anisotropic rocks. It also discusses the variation in the Mode I/Mode II fracture toughness ratio.