A fractal model for volume change dependency of the water retention curve

Khoshghalb, Arman; Pasha, Amin Y.; Khalili, Nasser

doi:10.1680/geot.14.t.016

Cited by 46 publications

(13 citation statements)

References 28 publications

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“…Numerous studies have shown that the radius and tortuosity of pores have directly affected permeability of porous media. , Also, a fractal theory could well consider these parameters and explain the flow behavior of gas in porous media. ,, Therefore, along with dynamic fractal dimensions and the critical capillary radius quantified in Sections and , the apparent permeability model for coal under the coupling actions of stress and water has been established.…”

Section: Establishment Of the Apparent Permeability Modelmentioning

confidence: 99%

Fractal Apparent Permeability Model for Coal under the Coupling Actions of Stress and Water

Duan

Gao

et al. 2023

Energy Fuels

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The environment of coal reservoirs is complex and variable, with various factors, not independent, but interlocking and coupled. However, their coupling effects have rarely been considered in previous theoretical studies. In addition, when a fractal theory was applied to analyze the permeability of coal, the linkage between fractal dimensions and the pore radius under external factors has usually been ignored. In this study, two parameters, pore compressibility and dynamic water saturation, were introduced to quantitatively represent the internal interactions between stress and water. Based on the results, dynamic fractal dimensions under the coupling actions of stress and water were obtained by considering variation in the pore radius and the assignment status of gas and water, following which an apparent permeability model of coal, with dynamic fractal dimensions, was established. The newly developed model was verified by reference to published experimental data. The results showed that stress dominated changes in the fractal dimension for pore-size distribution under the coupling actions of stress and water; however, changes in the fractal dimension for tortuosity was dominated, in turn, by stress and water. Subsequently, it was found that the fractal apparent permeability model could match the experimental data well. It revealed that the newly developed model could predict the evolution of coal permeability under dynamic changes in stress and water. Further, under the coupling actions of stress and water, the apparent permeability of coal possessed a positive correlation with the fractal dimension for pore-size distribution or water-dominated fractal dimension for tortuosity, while it was negatively correlated with the critical capillary radius or stress-dominated fractal dimension for tortuosity. In addition, the evolution of the apparent permeability was consistent with specific fractal dimensions and dynamic fractal dimensions, but the evolution of the slippage factor revealed an opposite result. Consequently, this initiates a new analytical perspective into investigating change mechanisms relating to coal permeability.

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Section: Establishment Of the Apparent Permeability Modelmentioning

confidence: 99%

Fractal Apparent Permeability Model for Coal under the Coupling Actions of Stress and Water

Duan

Gao

et al. 2023

Energy Fuels

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“…The experimental results of saturated tests are evaluated based on the effective stress principle (σ′v = σvuw). Simplified methods for calculation of unsaturated effective stress based on the single effective stress approach can be found in Khoshghalb and Khalili (2013) and Khoshghalb et al (2015). However, in this work, the experimental results of unsaturated tests are evaluated based on the vertical net stress (σvnet = σvua).…”

Section: Test Materials and Apparatusmentioning

confidence: 99%

Rate Dependency and Stress Relaxation of Unsaturated Clays

2019

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“…A critical step in modelling the behaviour of unsaturated soils is the determination of the soil water retention capacity at various suctions and hydraulic loading conditions (ie, main drying, main wetting, or suction reversals) at a given density state. A number of models are proposed to take account of the volume change dependency of the SWRC, eg, references herein . In this study, a void ratio–dependent SWRC similar to that presented in Pasha et al is adopted.…”

Section: Governing Equationsmentioning

confidence: 99%

“…A number of models are proposed to take account of the volume change dependency of the SWRC, eg, references herein. 82,[87][88][89][90] In this study, a void ratio-dependent SWRC similar to that presented in Pasha et al 82 is adopted. The salient feature of this model is that while it captures the volume change dependency of all branches of the SWRC (ie, main drying, main wetting, and scanning), it does not introduce any additional parameter into the formulation.…”

Section: Void Ratio-dependent Water Retention Curvementioning

confidence: 99%

Fully coupled elastoplastic hydro‐mechanical analysis of unsaturated porous media using a meshfree method

Ghaffaripour

Esgandani

Khoshghalb

et al. 2019

Num Anal Meth Geomechanics

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Summary This paper presents the first application of an advanced meshfree method, ie, the edge‐based smoothed point interpolation method (ESPIM), in simulation of the coupled hydro‐mechanical behaviour of unsaturated porous media. In the proposed technique, the problem domain is spatially discretised using a triangular background mesh, and the polynomial point interpolation method combined with a simple node selection scheme is adopted for creating nodal shape functions. Smoothing domains are formed on top of the background mesh, and a constant smoothed strain, created by applying the smoothing operation over the smoothing domains, is assigned to each smoothing domain. The deformation and flow models are developed based on the equilibrium equation of the mixture, and linear momentum and mass balance equations of the fluid phases, respectively. The effective stress approach is followed to account for the coupling between the flow and deformation models. Further coupling among the phases is captured through a hysteretic soil water retention model that evolves with changes in void ratio. An advanced elastoplastic constitutive model within the context of the bounding surface plasticity theory is employed for predicting the nonlinear behaviour of soil skeleton. Time discretisation is performed by adopting a three‐point discretisation method with growing time steps to avoid temporal instabilities. A modified Newton‐Raphson framework is designed for dealing with nonlinearities of the discretised system of equations. The performance of the numerical model is examined through a number of numerical examples. The state‐of‐the‐art computational scheme developed is useful for simulation of geotechnical engineering problems involving unsaturated soils.

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A fractal model for volume change dependency of the water retention curve

Cited by 46 publications

References 28 publications

Fractal Apparent Permeability Model for Coal under the Coupling Actions of Stress and Water

Fractal Apparent Permeability Model for Coal under the Coupling Actions of Stress and Water

Rate Dependency and Stress Relaxation of Unsaturated Clays

Fully coupled elastoplastic hydro‐mechanical analysis of unsaturated porous media using a meshfree method

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