The permeability tensor is a critical parameter for analyzing the hydraulic behavior of anisotropic permeability in fractured rock masses. However, determining this tensor for three-dimensional (3D) fractured rock masses has proven to be challenging and resource-intensive. Both field tests, requiring numerous costly in situ tests, and numerical experiments, hindered by complex discrete fracture networks with a high fracture density, present difficulties in obtaining accurate results. In response, this study proposes a semi-theoretical method for determining the permeability tensor of 3D fractured rock masses, significantly reducing labor and economic costs. The proposed method focuses on establishing the theoretical relationship of directional permeabilities in a 3D space, with emphasis on the properties of the permeability tensor and the influence of fractures' geometry on the flow rate. To facilitate the construction of the method, anisotropic ellipse and ellipsoid are introduced, providing a description of permeability anisotropy. With this innovative approach, engineers can calculate the permeability tensor even when only one value of permeability is available along any flow direction. The utilization of the anisotropic ellipse and ellipsoid concepts helps simplify the determination process. Through numerical experiments, the method is validated and its accuracy demonstrated, making it a valuable tool for analyzing the hydraulic behavior of 3D fractured rock masses.

The drainage consolidation method can reduce porosity to consolidate soft soils. In this study, a novel siphon drainage method is used as the drainage consolidation method to lower the groundwater level. Compared to other drainage methods, the siphon drainage method is power-free, environmental-friendly, and highly efficient. Numerical simulations are conducted to verify the feasibility of the siphon drainage method on soft soil treatment. In addition, the effects of soil permeability and drainage hole spacing on its application efficiency have been studied. The results show that: (a) The siphon drainage method can accelerate the consolidation by lowering the groundwater level; (b) The larger the soil permeability is, the faster the pore water pressure decreases; (c) Adopting 1 m hole-spacing in the siphon drainage is much more efficient than methods which have a 2 m hole-spacing. In addition, the siphon drainage method is proven the effective in soft soil foundation treatment by a field test in Zhoushan, Zhejiang Province.

Geometric predictive methods are efficient for determining the permeability of fractured rock masses, which evaluate the contribution of each fracture to the flow. However, the influences of fracture intersections are ignored during the calculation. In this study, influences of fracture intersections on the permeability prediction are studied. The result shows that the predicted flow rate can only have a good accuracy when there is an infinite-length fracture with a larger aperture. Based on this conclusion, three inferences for the applicability of geometric predictive methods are proposed: (a) for fracture networks where all fractures have infinite length, the predicted permeability can have a good accuracy; (b) for fracture networks containing both infinite-length and finite-length fractures, the predicted permeability is only accurate when the infinite-length fracture have a larger aperture; and (c) for fracture networks where all the fractures have finite length, the error rates of predicted permeability increase as the aperture ratios of fracture sets increase. Sixty-three sets of discrete fracture network models are generated for verification, and these numerical results validated our proposed inferences.

The discrete fracture model (DFM) is widely used in order to simulate the flow state of two phase flow in fractured reservoirs. There is a strong capillary pressure contrast between the matrix and the fracture in low-permeability reservoirs with conductive fractures. The physical quantities of the matrix-fracture interface change drastically and the flow pattern near the interface depends on the flow direction which make it very difficult to calculate the matrix-fracture exchange flux. New interface conditions are applied in this paper to get a scheme for calculating the m-f exchange flux. Based on new interface conditions the scheme for calculating the exchange flux is established. This scheme can improve the computational efficiency of the multi-phase flow in DFM since considering the discontinuous of physical quantities near the interface. The numerical test show that the proposed model has better performance than the traditional model.

The seepage capacity of fractured rock masses is a critical parameter in various engineering and geoscience projects. Due to the complex geometric distribution of fracture network, the permeability of rock masses typically exhibits an anisotropic behavior, necessitating detailed and comprehensive investigation of fracture characteristics to accurately determine permeability anisotropy in three-dimensional (3D) space. In this study, we developed an improved method for determining permeability anisotropy that significantly reduces the need for extensive input of geometric information. We employ the anisotropic ellipsoid, which is a mathematical representation of permeability tensor, to evaluate permeability anisotropy. Through in-depth mathematical derivation, we present a procedure for constructing the anisotropic ellipsoid using geometric trace information from a pair of orthogonal planes, which aligns well with the practical application scenario of underground tunnel excavation. Numerical experiments were conducted to validate our developed method. The mean prediction error rates were 5.2%, 16.8%, and 13.6% across three sets of experiments, experiments, demonstrating the validity of our approach.