Narrow Results

The complex microstructure of the surrounding porous rock of a tunnel has a significant influence on tunnel leakage. However, traditional tunnel leakage models are rarely able to quantify the interactions between the microstructure and macroscopic parameters of the surrounding porous rock of a tunnel, and the influence of the microstructure evolution on tunnel leakage. In order to quantify the contribution of the surrounding rock microstructure to leakage, a model capable of investigating the interaction between the evolution of microstructure and tunnel leakage behavior under the action of multi-physical fields is established based on fractal theory. The model couples the evolution of microstructure with the stress effect, adsorption–desorption effect, water pressure effect and surrounding rock deformation during tunnel leakage. The accuracy of the model is verified against experimental results, and the contribution of the surrounding porous rock pore size and pore distribution to tunnel water leakage is investigated. This study provides a theoretical basis and technical guidance for a reasonably accurate study of the tunnel leakage mechanism.

The pore geometry of porous rocks is fundamental for accurate description of stress dependence of effective permeability, which is an important parameter of mass transfer in porous rocks. An important physical assumption that porous rocks contain numerous elliptical or spherical pores has been shown to be successfully applied to many aspects of hydromechanical coupling properties of porous rocks. To investigate the detailed description of pore structures on the degree of effect on the coupled hydromechanical process, in this work, a generalized stress-dependent model for permeability of porous rocks has been proposed based on fractal geometry theory and mechanics of porous rock. The proposed model is expressed as a nonlinear function of pore structure parameters, such as aspect ratio (${\gamma }_{\sigma }$), the fractal dimensions ($D_{T,\sigma }$ and $D_{T,av}$) for tortuosity, the initial fractal dimension ($D_{f,0}$), and initial porosity (${\varphi }_0$) as well as matrix elastic constants ($E$ and $\nu$) of porous rocks without any empirical parameter. The validity of the proposed models is verified by the good agreements between available experimental data and theoretical predictions of stress-dependent permeabilities of porous rocks. Detailed discussions of the essential effects of pore structures parameters and material elastic constants of porous rocks on the dimensionless stress-dependent permeabilities are performed. It is found that the stress parameters ($E$ and ${\gamma }_0$) have remarkable effects on the dimensionless stress-dependent permeabilities compared with other parameters (${\varphi }_0$ and $\nu$). The proposed model may contribute to a better quantitative understanding of the coupled hydromechanical properties of porous rocks.

Mineral dissolution and precipitation reactions occur in a variety of porous rocks due to the deviations from a geochemical equilibrium between solid matrix and flow fluid, resulting in the alteration of the petrophysical properties of rocks. A physically-based theoretical model is proposed based on fractal theory for quantitatively assessing the temporal evolution of permeability for porous rocks undergoing mineral dissolution and precipitation reactions. The proposed model is associated with pore structure parameters, such as initial porosity $({\varphi }_0)$, the tortuosity fractal dimensions $(D_{T,t})$, the initial fractal dimension $(D_{f,0})$, and the overall dissolution rate $({\alpha }_t)$ considering the precipitation reactions in porous rocks. The proposed model provides a better prediction of the time dependence of permeability compared with the available experimental data. The essential effects of the overall dissolution rate and pore structural parameters of porous rocks on the dimensionless time-dependent permeabilities are investigated in detail. It is found that the overall dissolution rate has obvious effects on the dimensionless time dependence of permeabilities. The present model may provide useful insights into the understanding of permeability change during mineral dissolution and precipitation reactions in porous rocks.