Numerical study on progressive failure of hard rock samples with an unfilled undulate joint

Roughness is one of the most important parameters of unfilled joint. In this study, a series of numerical tests have been carried out on the progressive failure of rock masses with varied undulate joints. The numerical model reproduced the stress-strain relations obtained in lab tests on the marble samples with smooth joint under the confinement of σ3/σc = 0.013 and 0.27; meanwhile, the results of the numerical model on rock mass with rough joint indicated that with the increase of confining stress, the failure of rock mass presents as sliding along the rock joint (Type I), shearing partly through asperity and the joint (Type II) and mostly shearing through the rock block initiated by joint (Type III) respectively. To describe the progressive failure of hard rock samples with an unfilled undulate joint, an index of stress concentration factor (SCF) is presented as the ratio of σ1-σ3 (the localized principal stress difference of one point in the rock sample) to (σ1-σ3)o (the principal stress difference applied onto the rock sample) to denote the degree of heterogeneous stress induced by the undulate joint. It has been found that the progressive failure behavior is largely dependent on the joint roughness and the confining stress, which can be classified into 4 modes as: slipping plastic failure, slipping-shearing brittle failure, shearing brittle failure and shearing plastic failure. For the rock mass with rough joint, the crack initiation and propagation resulted from localized stress concentration at the turning point of rough joint during compression plays an important role in the progressive failure. For the rock mass with the same rough joint, SCFm decreases as the confining pressure increases because the confinement can weaken the heterogeneity of the rock mass.