Hard Rock Dilation Evaluation and Shear strength Approximation

Both mechanical and hydraulic behaviors of rock joints are closely dependent on joint aperture. Understanding how fracture wall-roughness affects dilation and shear behavior is important when modeling many subsurface problems. The main disadvantage of the previously proposed methods is that dilation determinations are carried out by determining 2D asperities height profile from one side of joint surface, whereas dilation is dependent on both surfaces asperity’s height. Also these methods propose a constant value for mechanical aperture whereas it will change during shearing. In addition, first order asperities and second order asperities have not equal effect on dilation behavior and the dilation is mainly controlled by undulation or first order asperities. In this paper, a new three-dimensional evaluation method of dilation using surface asperities height, under different shear displacements, is developed. This idealized dilation model is based on combined surface concept and wavelet theory and has capability to well understanding and approximating of shear strength during shearing. The modeling procedure of dilation and shear is reliable and conformity in the results of modeling and laboratory tests satisfactorily indicates success of the proposed method.