Abstract：Columnar jointed basalt is a typical jointed rock mass formed from the contraction of volcanic lava. The rock mass has “columnar mosaic structure” showing complex discontinuous，heterogeneous and anisotropic mechanical properties. The control of the unloading relaxation is thus a key problem to the construction of Baihetan hydropower station. Based on the research results in recent years，the geological origin and evolution of columnar jointed basalt are first described. The engineering classification of Baihetan columnar jointed basalt is then introduced. The discontinuity，the scale effect and the anisotropic mechanical property of the columnar jointed basalt are obtained through geological examinations，rock mechanics tests and numerical simulations. Based on the field monitoring and the numerical analysis on the relaxation deformation of the dam foundation and the underground cavern，the relaxation characteristics of the columnar jointed basalt are revealed. The anti-relaxation control measures of the dam foundation and the underground cavern in the optimization of structure shape and excavation support method are analyzed，and the supporting time and methods for relaxation control of the columnar jointed basalt are summarized. This study shows that the Baihetan columnar jointed basalt has significant unloading relaxation. Optimization of the structural shape can reduce the relaxation range. The anti-relaxation ability of rock mass can be improved by reinforcement measures before excavation. Support measures to alter the stress state immediately after excavation are effective to limit the spatial extension of relaxation.
2022, Vol. 41 
