The effect of scale on the geometric parameters of the rock joint surfaces

Summary:
In this study, three different natural joint geometries in dimensions greater than 2500 cm2 were selected from the field. The geometric parameters of the surface joints have been calculated from the scale of 50 × 50 mm2 to 500 × 500 mm2 and the effect of scale on these parameters and their variations with scale has been discussed.

The scale dependency of discontinuity surface roughness and shear strength has been investigated by many other researchers over the last three decades. Many of these studies have produced conflicting results. Some studies have shown a decrease in strength and roughness with increasing discontinuity size. Other studies have shown the existence of positive scale effects, a combination of positive and negative scale effects, or no scale effect. The present study attempts to investigate the effect of scale on the geometrical properties of rock joints.

Methodology and Approaches:
In this study, three natural smooth, undulating and stepped rock joints were prepared and their surfaces were scanned by 3D optical scanner. The surfaces were digitized and the geometric parameters were calculated by the code written in Matlab software. The geometric parameters were calculated for the square widows that were centered at the same locations and were measured from 50 × 50 mm2 to 500 × 500 mm2.
Results and Conclusions: The results showed that the effect of scale on various geometric parameters are not the same and will have different results depending on the distribution of primary (waviness) and secondary (unevenness) roughness. The angular parameters of rock joint surfaces, in the scale of greater than 400 cm2, are independent of scale. However the amplitude parameters of rock joint surfaces, in the surfaces with dominant waviness, increase with increasing of scale (at least up to 2500 cm2)