Abstract: Due to the distinctive formation mechanism of columnar joints, columnar jointed basalt exhibits strong discontinuity and anisotropy. The columnar jointed basalt rock mass in Baihetan project is selected as a case study. The structural control effect on the equivalent modulus of deformation is discussed by using jointed finite element method (JFEM). The results show that, on the transverse plane, the equivalent modulus of deformation increases with the column irregularity, which increases about 10% from completely irregularity to completely regularity. This trend also agrees with the increase of the column size. The equivalent modulus of deformation corresponding to a side length of 0.1 m is 5.36 GPa, and this value increases up to 23.4 GPa for a side length of 0.5 m. Columnar joints rock mass may be considered as isotropic on the transverse plane, and basically, the equivalent modulus of deformation varies correspondingly with joint stiffness. But when it comes to the longitudinal plane, the wider joint spacing of the joint set 2 is, the higher equivalent modulus of deformation is. The equivalent modulus of deformation increases firstly then decreases, and reaches its maximum value when the cross-bedding ratio is 50%. The equivalent modulus of deformation on the longitudinal plane shows a similar correspondence relationship with the joint stiffness on the transverse plane. The simulation results obtained by JFEM agree well with the existing field observations and 3D numerical studies.

Key words: columnar jointed rock mass, equivalent modulus of deformation, structural effect, jointed finite element method, column irregularity