Up to now, several parameters and methods such as empirical, statistical method, fractal and spectral methods are used to quantify the rock joints surface. Spectral method is the latest method and more comprehensive. One of the most useful tools in spectral method is the Fourier transform. Due to the ability of the Fourier analysis in separating signals to different amplitudes and frequencies, it can separate the roughness profile to some profiles with specific frequencies and amplitudes. Profiles with high frequencies and low amplitudes represent the small asperities and profiles with low frequencies and high amplitudes represent waviness. In previous investigations, Fourier analysis is used to find power spectral curve and roughness parameters or fractal dimension were calculated by this curve. However, in this paper with applying Fourier analysis on profiles and then applying low pass filter on the profiles and investigating the effect of cut-off frequency in low pass filter of JRC profiles on real length and average dip angle, new parameters (CL & CI) are introduced to quantification of rock joints roughness. These parameters have a high correlation with JRC. Since, CI can quantify the influence of shear direction, CI represents roughness
In geomechanics engineering, the engineers are faced to several problems, which are caused by geotechnical systems and their structures are located in or on jointed rock masses. In rock masses, joints have complex structures and patterns. Due to this matter and inherited uncertainty in estimating geomechanical properties of intact rocks and joints, predicting of rock masses properties is difficult task. On the other hand, the limitation of the experimental and field data makes it much worse. In order to predict hydraulic and mechanical properties of rock masses, a) joint network geometry, b) hydraulic and mechanical properties of rock joints, c) hydraulic and mechanical properties of intact rock should be quantified .
The shear behavior of unfilled joints is dependent on rock type, normal stress on the joint plane, boundary conditions, geometry of the rock joint surface, roughness, rock joint scale, degree of alteration, moisture and water pressure .