Experimental Study of a Reconstruction Method for Rock Joints in Sandstone Based on 3D Laser Scanning and 3D Engraving Techniques

The shear behaviour of natural joints generally exhibits anisotropy due to variations in morphological characteristics. The anisotropic shear behaviour of natural joints mainly determines the rock mass stability. It is improbable to sample a large number of natural joints with same surface morphologies in the field. In this study, 3D laser scanning and 3D engraving techniques were adopted to reconstruct natural joints in the laboratory. In the reconstruction process, a series of trial and error engraving tests were conducted due to the lack of engraving resolution evaluation and engraving parameter selection methods. Both 2D and 3D characterization methods were used to quantitatively assess the engraving resolution. A method was proposed to determine the interval path based on the cone angle of the cutter. A series of engraving tests were conducted to study the effect of the path interval on the engraving resolution and to verify the proposed method. The results indicated that the engraving path interval should not be too large (> 0.20 mm) or too small (< 0.10 mm), which could result in a strip between adjacent engraving paths or overengraving, respectively. The natural joints in the sandstone specimen could be successfully reconstructed when the optimal cutter radius and path interval were 0.40 and 0.10 mm, respectively. The root mean square error (RMSE) of the profile height between the original and reconstructed joints was less than 0.10 mm. The difference in the 3D roughness (theta(max)*/C+1)) between the original and engraved joints was less than 0.5. The methods proposed in this study can be employed to accurately assess the engraving resolution and to quickly determine reasonable engraving parameters. In this way, natural joints can be reconstructed with high engraving resolution. The anisotropic shear behaviour of natural joints can be suitably investigated in the laboratory.