ABSTRACT:
In numerous studies, an internal flaw has been investigated with a ‘through’ model (2-D). However, crack growth induced from a flaw tip within a rock mass is three-dimensional. And some flaws may often be filled with water. In this study, a series of computerized tomographic (CT) real-time testing with rocklike specimens were conducted with triaxial loading equipment containing a CT machine. The internal flaw in some specimens was injected with water under controlled pressure by a special piston. The entire process of crack propagation inside the specimen was recorded by the scanning images. It is shown that the peak fracture stress of the internal flaw under triaxial compression is much higher than that of uniaxial compression. The relation of damage variation versus confining pressure is also established. The threshold value of damage evolution is provided.
1 INTRODUCTION
A number of different scales (micro, meso and macro scale) of defects (flaws) exist in fractured rock masses. Under compressive stress, the initiation, propagation and interaction of micro to macro flaws will weaken the stiffness and strength of the rock mass. The failure of brittle materials, such as rocks and concrete, results generally from crack initiation and propagation. Horri & Nemat-Nasser (1985), Reyes et al. (1991) and Dyskin et al. (1994) conducted a series of tests on the propagation of inclined flaws in brittle materials subject to uniaxial and triaxial compression; Zhao et al. (1993) conducted studies using the SEM method to determine coring effects and the propagation of micro-flaws in rocks; Yang (1998), Ge et al. (2000) Jian et al. (2004) and Chen et al. (2005) used a scanning electron- microscope and computerized tomograph (CT) unit to conduct experimental investigations on the distribution of mesoscopic damages and the damage evolution process of rocks under compression.
