Experimental Study on Seepage Characteristics of Columnar Jointed Rock Mass with Different Cross-Section Shapes

With the construction and commissioning of major hydropower projects represented by Baihetan of Jinsha River, it is of great significance to clarify the mechanical and seepage characteristics of engineering rock mass under complex stress environment represented by high confining pressure and high water pressure. Based on the field survey data and the structural characteristics of columnar jointed rock mass, this paper takes the columnar jointed basalt of dam foundation as the research object, and two kinds of columnar joint similar material model samples with different dip angles β of quadrangular prisms and hexagonal prisms were prepared, and the true triaxial stress-seepage coupling test was carried out. The test results show that the columnar jointed rock mass with different cross-section characteristics has strong permeability anisotropy, and the permeability coefficient k is positively correlated with β under different loading stages. During the true triaxial loading process, the volume strain εV of the sample can be used as an effective characterization parameter of k. In the volume compression stage, k shows a low level, and the volume expansion stage k shows a rapid growth trend. The final failure mode of the specimens shows three typical forms, the most dangerous failure mode is the structural failure dominated by the shear slip failure of the joint surface, which main occurs in the specimens with β=45°,60°. Correspondingly, the lateral support of this kind of rock mass should be strengthened in the construction design of tunnel surrounding rock and dam foundation rock mass.