Abstract
Permeability is an important physical property of rock. In rock and rock-like materials, permeability after yielding is closely related to plastic flow behavior. Theoretical analysis and experimental investigations are effective and reliable ways of studying the evolution of permeability. In this paper, fluid flow tests of sandstone samples under 11 stress states were conducted using the MTS 816.02 rock mechanics testing system and a self-designed permeation system. A new plastic flow rule was proposed based on the Mohr-Coulomb yield criterion and a nonassociated flow rule. The applicability of the flow rule was verified by comparing the estimated and experimental values of the equivalent shear strain of the Mohr–Coulomb criterion. Two new coefficients were defined to reflect the influence of the volume deformation and shear deformation on the permeability. A permeability model for plastic flow was established, which can be used to calculate both single-step and multistep permeability estimates of the sandstone samples during plastic flow. The errors of both estimation methods were analyzed. The experimental results showed that the plastic multiplier for the sandstone samples was positive during unloading conditions and negative during loading conditions. The experimental value error of the single-step permeability estimation was less than 16.5%. The experimental value errors of the multistep permeability estimations varied between 15.6% and 16.7%, indicating that the iterative format of the multistep permeability estimation method was generally stable and highly precise. A comparison of the permeability influence coefficients indicated that the influence of the equivalent shear strain on the permeability was smaller than that of the volumetric strain.
Highlights
Sandstone is the primary type of sedimentary rock in which rock engineering problems arise, such as water disasters in coal mining engineering
A fluid flow test was conducted using the MTS 816.02 rock mechanics testing system and a selfdesigned permeation system to obtain the values of permeability under different stress states
The proposed iterative formats of the plastic multiplier and permeability estimations were based on the permeability model
Summary
Sandstone is the primary type of sedimentary rock in which rock engineering problems arise, such as water disasters in coal mining engineering. Water inrush through roof or floor sandstone aquifers has become a serious problem that occurs in some deep coal mines [1]. Water inrush can happen in coal mines when roof or floor sandstone aquifers have well-connected major flow paths. Fluid flow research of sandstone roof or floor under mining-induced stress conditions is the fundamental study on water inrush. The permeability evolution of sandstone is the key to studying the fluid flow behavior under mining. In the process of coal mining, deformation on the sandstone roof and floor is dominated by plastic displacements. Investigating the permeability evolution of sandstone under plastic deformation is essential
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