Recent rock fracture mechanics developments

Rock fracture mechanics dates hack to mid 1960 and its application to rock hurst prohlems and collapses in deep gold mines of South Africa. The theory of fracture mechanics provides a means of determining the fracture stress of a stnrcttrre in material containingflaws or microcracb of known size and orientation in terms of a stress intensity factor K Tension mode (Mode I) or mired tension and shear mode (Uode I and II) fracturing are most important in rock mechanics and rack engineering. A new rack fracture toughness testing in Mode II called Punch- firinrgh Shear Te~LtY introduced and e-rperimental resultsf or three dryerent rock tjpes tested at dgfferent confining presstrre are presented. Frachrre toughness data are used for simulation of mired mode fracture propagation of rocks with a new strain energy release rate criterion, called F-criterion. The criterion has heen implemented in a new fracture mechanics program called FRACOD? The basic features of the code are given and resultf rom simrrlation~o f horehole breakouts and fracture propagations around a canister horehole for disposal of .spent nuclear frrel are presented.