Abstract

Triaxial compression tests were performed on physical models of a rock-like material with parallel non-persistent joint sets. Although many investigations on the coalescence of discontinuous joints exist, they usually have studied this phenomenon using uniaxial or biaxial tests. In this study, the triaxial tests allowed analysing the effect of the confining stress on the coalescence of the existing joints. The development of new cracks, coalescence and the failure mode were inferred from observation of the failed specimens. The results show how the new cracks generate and propagate, connecting the existing joints. Mainly three coalescence types were observed, with additional variations and combinations depending on the applied confining stress and joint geometry. The failure modes can be associated with the strength and degree of ductility of the failure behaviour.

1 Introduction

The strength and deformability of the rock mass is controlled by its discontinuities. Discontinuities along a same plane separated by intact material are referred to as non-persistent or discontinuous joints. The failure of the rock mass depends on the propagation and coalescence of these discontinuities during loading.

A large number of investigations have been carried out for the study of the coalescence of non-persistent joints. They include investigations on specimens containing one or multiple discontinuities in natural rock and in artificial materials (Brown 1970; Reyes and Einstein 1991; Bobet and Einstein 1998; Vasarhelyi and Bobet 2000; Wong et al. 2001; Sagong and Bobet 2002; Prudencio and Van Sint Jan 2007; Yin et al. 2014; Cheng et al. 2016; Yang et al. 2017). Most of these investigations have studied the effect of the discontinuous joints in the deformation and strength and have analysed the coalescence and propagation of the cracks.

This work presents the results of triaxial and uniaxial compression tests performed on physical models of a rock-like material with parallel non-persistent joint sets. The triaxial tests allowed studying the effect of the confining stress on the coalescence of the existing joints and the resulting mechanical properties and mode of failure. The failure mode and its relation to the mechanical and geometrical properties were analysed.

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