Direct Shear Test Modelling to Analyse the Behaviour of Joints in Adjacency of a Tunnel

In modern times, the necessity of tunnel construction is inevitable with regards, to the development of the transportation industry, and as a result it is very important to analyse its stability while it is adjacent to some geologic features, such as discontinuities. The direct shear test is one of the most applicable geotechnical tests to investigate geological features such as joints and discontinuities. The dilation and shear behaviour of two sliding surface can be analysed with this test, and in this paper, a constant strain joint element has been presented and a combination of a slider and a shear spring have been applied to this joint element to model the plastic shear behaviour of the joint in contrast to previous joint models. Then, the direct shear test has been programmed based on the finite element method in MATLAB. Subsequently, the joint behaviour has been analysed with an increasing normal stress with various shear stiff¬ness values and JRC (Joint Roughness Coefficient). The results of this numerical study demonstrate that the shear displacements reduce with an increase in shear stiffness, and consequently the dilation decreases as well. Meanwhile, by increasing the normal stress, the joint experiences more dilation in spite of a reduction in the rate of increasing the dilation. Moreover, the peak shear stress and shear strength of the joint have been increased as the JRC increases, but the effect of the normal stress on the shear strength increases with greater significance than with the JRC. Also, the increase in JRC has a direct relationship with dilation increase in the joint.