Structural analysis of fractures around underground excavations on a Witwatersrand gold-mine

Abstract

The interpretation of faults and joints on the bas is of stresses in the earth I s crust has been attempted on many occasions. The main problem encountered in such interpretations has been that the physical conditions, and the stress field, during the period of origin of these faults were imperfectly known. New information has become available with regard to the mechanisms involved in fracture processes, primarily in the development of the modified Griffith criterion of fracture initiation. The validity of this criterion is tested by comparing orientations of fractures as predicted with those measured in a known environment. Fractures in the hanging wall of a s tope were measured on a gold-mine in the Klerksdorp area. Comparison of predicted and measured orientations shows that the limits within which the orientation of fractures must be, can be predicted. However, minor variations within these limits indicate that a more elaborate model than an idealised slit in an elastic medium is necessary. The modified Griffith 1 s criterion of fracture is used to analyse the history of faulting at the Loraine Gold Mine in the Orange Free State. The studies show that it is possible to place certain limiting conditions on the physical properties of the material, and the stress fields existing at the time of origin of the fault systems.