NUMERICAL SIMULATION OF FRACTURE MECHANISM OF COLUMNAR JOINTED BASALTS WITH DIFFERENT SHAPES UNDER COMPRESSION¹⁾

The strengths and deformations of columnar jointed basalts (CJBs) with different shapes are different under compression, and the fracture mechanisms and failure patterns are also different. In this paper, the images of CJBs with different shapes are constructed. Then, by combining meso-damage mechanics, statistical strength theory and continuum mechanics, the images of CJBs are transformed into finite element mesh models based on RFPA$^{\rm 3D}$-CT digital image processing, and mechanical parameters of joints and rock materials are assigned respectively, in which the heterogeneity of joints and rock is considered. Further, numerical tests of CJBs under different lateral pressures are carried out to study their strength and deformation characteristics, fracture mechanisms and failure patterns. The results show that for the case under the lateral pressure of 0~MPa, the compressive strength of CJBs (with dimensions of 1.5~m$\times$3~m, 3~m$\times$3~m and 6~m$\times$3~m) generally exhibits U-shaped distribution with the increase of column dip angle; under the lateral pressure of 6~MPa, the compressive strength generally exhibits V-shaped distribution with the increase of column dip angle. For CJBs with dimensions of 1.5~m$\times$3~m and 6~m$\times$3~m, and column dip angles of $\beta=15^\circ$ and $\beta=45^\circ$, the fracture mechanisms and failure patterns under different lateral pressures are studied. The whole processes of stress concentration, crack initiation, propagation, fracture strip zone formation and acoustic emission characteristics are analyzed.