Abstract:

Quantitative evaluation of the permeability and anisotropy of fractured rock masses is crucial for engineering geological investigations in water conservancy and hydropower projects. Such evaluations provide essential technical support for designing anti-seepage curtains, foundation pit drainage systems, and predicting water inrush in hydraulic tunnels. In this paper, we introduce a method for estimating the hydraulic conductivity tensor of nearly horizontally layered fractured rock masses based on “seepage-stress” coupling theory. This method integrates conventional vertical borehole water pressure tests, horizontal directional borehole water pressure tests, and rock mass stress tests. By establishing a negative exponential function relationship between normal stress and aperture, the equivalent hydraulic aperture of the structural plane is estimated, and the hydraulic conductivity tensor of the rock mass is calculated. This method has been applied to the Guxian water resources management project on Yellow River as a case study. The anisotropy of the hydraulic conductivity in the dam site area was analyzed. Results demonstrate that, compared with conventional vertical borehole water pressure tests, the proposed method better characterizes the permeability and anisotropic properties of the rock masses. Specifically, the comprehensive permeability coefficient obtained using the proposed method is approximately 15 times that of conventional tests, providing valuable scientific guidance for the design of seepage control engineering.

Key words: fractured rock mass, hydraulic conductivity tensor, directional water pressure test, in-situ stress test, Yellow River Guxian water resources management project