Mechanical response and failure mechanism of inclined rough jointed rock under true triaxial compression loading

Abstract

Rock-like specimens containing a joint with different inclination angles and roughness were prepared using 3D printing technology. Then, true triaxial compression loading experiments were conducted on those jointed specimens. The increase in roughness leads to an increase in the axial strength and peak strain. With the increasing inclination angle, the axial strength initially decreases from 30° to 60° and then increases from 60° to 90°. While the peak strain first rises from 30° to 45° and then declines from 45° to 90°. The variation in failure mode results from differences in lateral stress on the joints under different strike directions. Specimens with joint strike parallel to the intermediate principal stress predominantly showed matrix or matrix-joint mixed shear failure, whereas those parallel to the minimum principal stress exhibited matrix shear failure. The analysis results of acoustic emission signals indicate the crack number and shear crack percentage increase with the increasing roughness and first decrease (30° to 60°), then increase (60° to 90°) with the increasing inclination angle. The research results can provide some guidance for the design and support of underground engineering with jointed surrounding rock.

1. Introduction

Numerous discontinuities, such as beddings, faults and joints, are generated under various geological movements [1−3]. Those discontinuities will likely induce geological hazards when excavation works are carried out near the rock mass containing them [4, 5]. As widely existing discontinuities in rock mass, joints play a major role in controlling the deformation and failure of rock mass [6, 7]. Therefore, the effect of joints on the mechanical and failure characteristics of rock is always a focus in geotechnical engineering.

For slope engineering and shallow-buried rock mass engineering, the load on the joint upper wall is small, and the instability of the jointed rock is mainly manifested as a shear slip along the joint plane [8, 9]. The present research on rough jointed rock (RJR) specimens mainly focuses on the shear behavior of rough joints under different loading methods [10, 11], boundary conditions [12, 13] and filling conditions [14 −17]. For deep-buried rock mass engineering, the higher ground stress environment of the jointed rock makes the mechanical deformation and fracture characteristics of jointed rock mass more complex [18, 19]. However, the normal stress applied on the joint in the direct shear test is usually small (<20 MPa); besides, the influence of joint dip angle (α) is not considered, which cannot reflect the stress state and occurrence condition of deep buried jointed rock mass [20, 21].

Therefore, many experimental and numerical studies on the jointed rock under a high-stress state have been carried out, and some conclusions have been proposed. ASADIZADEH et al [21, 22] conducted uniaxial compression tests on rock-like specimens containing two rough closed joints. The results showed that mechanical properties were positively correlated with joint roughness coefficient (JRC). LIU et al [23] carried out uniaxial compression experiments on granite specimens with “Y” shaped cross joint specimens with fixed dip angle and different JRC, and the results showed that the variation of JRC greatly changed the fracture mode of the specimen. INDRARATNA et al [24] used gypsum specimens containing saw-tooth joints to study the effects of filling thickness and water content on the shear strength of filled joints under different confining pressure conditions. SAADAT et al [25] used the discrete element method to carry out a numerical simulation of the conventional triaxial compression (CTC) of jointed rock with different JRC and found that the rock matrix would produce tension cracks into