Investigation on the scale dependence of shear mechanical behavior of rock joints using DEM simulation

Estimating the shear mechanical parameters of field-scale joints using laboratory tested results is a challenging task due to the scale effect. To further understand the effect of specimen size on shear mechanical parameters, this study not only focuses on the joint length effect, but also explores the effect of specimen height (the dimension in the direction perpendicular to the joint surface), while the latter has not been paid enough attention in the existing studies. Based on the particle discrete element method, numerical direct shear experiments are carried out for multiple specimen height and joint length conditions. The effects of specimen height and joint length on the pre-peak, peak and post-peak shear deformation stages are analyzed in detail. The results suggest that specimen height also has an effect on the shear mechanical parameters of the joints. In the pre-peak deformation stage, the specimen height effect on shear stiffness is diametrically opposed to that of joint length, while the effect on shear strength is similar to that of joint length. In the post-peak crack evolution stage, the specimen height effect also differs from the joint length effect. In terms of significance, the effects of specimen height and joint length on the same shear mechanical parameter are almost at the same level. Therefore, future experimental studies may need to pay more attention to the specimen height effect.