Time-dependent process of crack growth and failure of brittle rock are simulated with the numerical modeling approach using PFC (Particle Flow Code) which can visualize progressive and dynamic behaviors of deformation and failure in time domain.A model of Brazilian fracture toughness test is used and the influence parameters on the generation and extension of crack are analyzed such as shape of loading plane, loading angle and loading rate. For the loading rate less than 0.01 mm/s, tensile crack is initiated at the center of Brazilian disc model and the stable crack growth can be controlled. Mode-I fracture toughness evaluated is almost constant for this loading rate. Strength of rock is dependent on the loading rate and the stress level of creep loading. It can be said that the failure criterion under the extremely low loading rate gradually approaches the long-term strength of rock.
The unstable behaviors of rock structures in static and quasistatic conditions commonly happen due to fatigue failure by the long-term creep deformation or due to crack generation by the change of the environment. The example of the environmental change is stress change induced by the thermal source like LNG or radioactive waste. These unstable mobilizations of rock cracks cause the progressive degradation of rock strength and finally result in the collapse of tunnel roof, sliding failure of rock slope, leakage of storage materials, etc. The estimation and prediction of time-dependent process of instability and failure in long-term, from tens to hundredsof- thousands of years, is very important especially for safe management of old rock structures. In this study, the time-dependent process of destabilization and failure of rock structures is simulated with the numerical modeling approach. The numerical simulation is carried out using PFC (Particle Flow Code) which can visualize progressive and dynamic behaviors. The time-dependent deformation and failure behaviors in creep are analyzed and the macro crack extension and safety criterion are discussed. Model of Brazilian fracture toughness test is used and the influence parameters are analyzed such as shape of loading plane, sizes of Brazilian disc and unit particle of model, loading angle and loading rate.
The time-dependent process of crack initiation and growth of rock is simulated with the numerical modeling approach using PFC. Model of Brazilian disc is used for the numerical simulation. Experimental and numerical researches for the crack growth and fracture toughness using Brazilian disc specimen have been carried out by Guo et al. (1993), Wang et al. (1999), etc. The distribution of the maximum tensile stress according to the loading angle and the distance from the disc center is shown in Figure 2. The location of the maximum tensile stress varies with the loading angle. It approaches to the disc center under the condition that the loading angle, α, is larger than 10 degrees.
