A nonlinear peak shear strength criterion

proposed by Maksimovic

uses a simple hyperbolic function to describe the peak dilatancy angle under different normal stresses. The model has significant advantages

such as parameters have physical meaning

law is valid from zero to infinity

and it is simpler from the view of mathematical point. The roughness of joint surface is expressed by the parameter of “roughness angle

”

obtained by using the least square fit method on basis of at least three sets of measured data. It is not easy to use the Maksimovic criterion to predict the peak shear strength of rock joints. In this paper

the roughness angle is determined by a rational method with a quantitative three dimensional morphology parameters of joint surface. Then

a modified Maksimovic peak shear strength criterion is proposed. Several experimental results are used for verification of the proposed relations. It is shown that the calculated values are in good agreement with the measured data. It also presents the comparison between the new criterion with the famous Barton’s criterion. We can use the proposed criterion as a useful tool to predict the peak shear strength for rock joints.