Coupling model of saturated fissured porous media based on porosity-dependent skeleton strains and nesting concept

Abstract

To guide the constitutive modeling of saturated fissured porous media considering dual porosity changes, it is necessary to formulate a general constitutive theoretical framework using two porosity-dependent skeleton strains. First, two nesting ways are introduced named Modeling-method 1 and Modeling-method 2. Based on Modeling-method 1, a linear elastic model with fully coupling is obtained after solid and fluid strains are expressed as the combinations of strain state variables, respectively. The approaches to measure its elastic coefficients are introduced. Second, as a symmetric model, another elastic model is established from Modeling-method 2. The transformation expressions of elastic coefficients between different models are formulated using linear algebra. The results reveal the application scope of Berryman & Wang thought experiment. When the state variables are completely decoupled, the elastic model is degenerated into Khalili & Valliappan model. Meanwhile, Hypotheses 1 and 2 generally do not hold simultaneously. Finally, the evolution process of dual-porosity along with the consolidation of a soft fissured rock mass layer is analyzed. The results show that the fissure porosity varies far more greatly than the pore porosity. The derivation of constitutive equations based on mixture theory and nesting concept is relatively trivial, but can provide insight into constitutive characteristics.