The Barton’s shear strength criterion is widely used in engineering practice. However

the estimation of joint surface roughness coefficient (JRC) is subjective and one-sided in this method. Therefore

a method is proposed to estimate JRC with multifractal parameters based on multifractal theory. Firstly

3D data of joint surface are obtained with digital image processing (DIP) technique. Secondly

the fractal dimension of surface is calculated with the projective covering method (PCM). Particularly the multifractal parameters of fifteen joint surfaces are computed. The results show that the rougher the surface

the larger the parameters of and . Both multifractal parameters and can well describe the morphology of joint surface. At last

nine groups of gypsum specimens are used for direct shear tests under different normal stresses. The relationship between the multifractal parameters and the JRC is examined with the principle of least square method according to the experimental data of shear strength. Thus

the JRC can be estimated accurately using parameters of and . The results provide a new approach to study surface roughness of rock joints. On the basis

the shear strength of rock joints can be accurately estimated.