This study presents the results of laboratory diametrical compression tests performed on Brisbane tuff disc specimens to investigate their mode-I fracture tough-ness response to static and cyclic loading, as a function of the applied load. Fracture toughness (KIC) is an important material parameter that corresponds to the critical state of the stress intensity factor required for crack initiation and subsequent propagation. The static and cyclic loading tests were carried out on Cracked Chevron Notched Brazilian Disc (CCNBD) specimens prepared from Brisbane tuff cores. Two different types of cyclic loading were applied:
cyclic loading with constant mean level and constant amplitude, termed sinusoidal cyclic loading, and
cyclic loading with increasing mean level and constant amplitude, termed increasing cyclic loading.
The fracture toughness response to cyclic loading was found to be different from that under static loading in terms of the ultimate load and damage mechanism in front of the chevron crack. A maximum reduction of the static KIC of 46% was obtained for the highest amplitude increasing cyclic loading test. On the other hand, for sinusoidal cyclic loading, a maximum reduction of the static KIC of 30% was obtained. These reductions clearly illustrate the dramatic effect of cyclic loading on the fracture resist-ance of cracks in rocks.
Some rock structures such as bridge abutments, dam and road foundations, and tunnel walls undergo both static and cyclic loading caused by vehicle-induced vibrations, drilling and blasting, traffic, etc. This type of loading often causes rock to fail at a lower stress due to effect of rock fatigue. A limited amount of research on rock fatigue was published before 1970. They found that the force required to cut hard rock was reduced up to 60 to 70% using ODC technology compared with that required using conventional techniques.
