Three-dimensional finite element simulation and reconstruction of jointed rock masses for bench blasting

Abstract

During the numerical simulation of blasting in jointed rock masses, the accuracy of joint geometric parameters is one of the key factors affecting the numerical results. To facilitate the numerical simulation, most of the previous studies on blasting in jointed rock masses were conducted on regular jointed rocks, which is not conducive to fully revealing the dynamic responses and blast-induced damage characteristics of jointed rock mass. In this study, scanline sampling and borehole sampling were employed to obtain the surface and internal joint structures of the rock bench. To represent the joint geometry, a reconstruction technique for three-dimensional (3D) jointed rock masses in LS-DYNA was proposed utilizing MATLAB code. In the process, the elements on joint surfaces were identified and assigned mechanical parameters of joints to construct the 3D jointed rock model, where the geometrical properties of generated joints obey the statistical distribution obtained from the scanline survey. Taking an open-pit limestone mine as an example, a statistical analysis of the 3D distribution of joints was carried out and used to construct a 3D jointed rock numerical model for bench blasting. Comparisons between the bench slope extracted from the numerical model and the actual joint trace mapping from a rock exposure are performed, and the similarity between the two contour plots of joint orientations reaches 91.6 %. For comparison tests, the bench blasting was simulated by an intact rock model and the jointed rock model. The results indicate that the dynamic responses and blast-induced damage characteristics of jointed rocks are significantly affected by the geometry of joints. Compared with the intact rock model, the presence of joints causes stress concentration and local strengthening of rock damage between adjacent joints, which results in a 30.5 % increase in the damage volume. Furthermore, a field blasting test was conducted to analyze the accuracy of the jointed rock model. The results show that the fragment size distributions obtained from the jointed rock numerical model and the filed test are generally consistent, and the error between them in the proportion of rock fragments with a size of 0 ∼ 100 mm is only 12.8 %. These findings indicate that the proposed reconstruction method of the jointed rock model is considerably robust for characterizing the joint geometry of in situ rock masses and simulating the bench blasting in jointed rock masses.