Experimental research on pre-existing cracks in marble under compression

An experimental approach on propagation and coalescence of pre-existing cracks in marble samples under compression is carried out. It is shown that the influence of pre-existing cracks is significant,and the critical collapsing load, failure stress and elastic modulus are all reduced. Many forms of wing cracks initiated from the tips of pre-existing cracks are observed, for example, tension mode wing crack, shear mode wing crack and reversed wing crack. The orientations of pre-existing cracks can decide which kind of wing cracks will be produced. The interactions between cracks are of marked influence on the initiation and propagation of wing cracks, and make failure manners of samples thoroughly different. The initial angles of wing cracks in marble range between 52°～68°, which are lower than the results (about 77°) of previous experiments on model materials. This indicates that the model materials cannot simulate fully the characters of the real rock materials.