ABSTRACT
As rock materials are weak in tension, fracture tests should preferably be conducted with compressive loading in such a way that tensile fractures are induced. Use of more than one type of specimen is regarded as appropriate when it is required to measure the fracture toughness of anisotropic materials in different material directions of a rock sample. A number of standard methods have been proposed to determine the mode I fracture toughness of rock. International Society for Rock Mechanics (ISRM) has given three recommended methods for static load test (ISRM Testing Commission. 1995, Kuruppu et al. 2014, Chong & Kuruppu 1984, Kuruppu & Chong 2012), which include those based on Short Rod (SR) specimen, Chevron Bend (CB) specimen, Cracked Chevron Notched Brazilian Disk (CCNBD) specimen and Semi-Circular Bend (SCB) specimen. The Cracked Straight Through Brazilian Disc (CSTBD) specimen has also been widely used for
1 INTRODUCTION
1.1 Type area
Rock fracture mechanics can be used to identify and predict the imminent failure of rock mass structures thereby providing guidelines to improve the stability and the safety of these structures. Another application is for the exploitation of mineral resources by adopting techniques such as mechanical mining, blasting and hydraulic fracturing. In fracture processes which are not associated with high strain rates, the mode I plane-strain static fracture toughness gives the critical value of the stress intensity factor leading to the onset of crack growth in that mode. Some of the applications of fracture toughness include index of fragmentation processes like those used in tunnel boring, a modeling parameter in processes such as rock cutting and hydraulic fracturing and for the stability analysis of civil, mining and earthen structures.
