ABSTRACT: In order to investigate the influence of joint geometric parameters on the mechanical behaviors of jointed rock masses, the compression shear test was carried out. The joint dip angle and joint overlap were varied to alter the relative positions of parallel joints in geometry. The failure mode of the joint specimen under compression-shear loading can be classified into four types: coplanar shear failure, shear failure along the joint plane, shear failure along the shear stress plane and similar integrity shear failure. The joint dip angle has a decisive effect on the failure mode of the specimen. The shear strength of specimen firstly increases and then decreases with the increase of the dip angle, and peaks at 45°. The shear strength decreases with the increase of the joint overlap. The shear stress-displacement curves of different joint inclination samples have differences which mainly reflect in the post-rupture stage.
The risk assessment of rock masses is a common task in rock engineering. The discontinuities such as joints, faults and bedding planes in the natural rock mass greatly weaken the stability of the rock mass. These discontinuities control the mechanical properties of rock mass not only because of their interaction with the intact rock, but also because of the interaction between themselves (Wang et al. 2017). When the specimen is loaded, new cracks develop near the tips of existing joints and propagate or coalesce with other cracks. The propagation of new cracks and the coalescence of fractures lead to a degradation in the mechanical properties of the rock. The effect law of joints on the failure of rock mass will have important guiding significance for actual engineering.
The mechanical behavior of non-persistent jointed rock mass has been extensively studied by experiments and numerical simulation. Cao et al. (2016) investigated the peak uniaxial compressive strength and failure patterns of ubiquitous-joint rock-like specimens by combining similar material testing and numerical simulation. The failure patterns of ubiquitous-joint specimens can be classified into four categories. Bahaaddini et al. (2013) studied the effect of joint geometry parameters on the deformation modulus, compressive strength and failure mode of the rock mass by particle flow modeling. Using photographic monitoring and acoustic emissions monitoring techniques, Yang et al. (2013; 2016) investigated the relationship between the real-time crack coalescence process and axial stress-time behavior for a red sandstone containing two unparallel fissures. Chen et al. (2014; 2014) studied the influences of joint inclination angle and joint connectivity rate on compression strength and stress-strain curves of rock mass with non-persistent open joints by conducting uniaxial compression tests on gypsum specimens. To explore the influence of joints on strength and failure mode of the rock mass, Pu et al. (2010) used the rock-like material with different angles and densities of distribution of the fissures to conduct the experiment.