Macroscopic definition of Bishop’s χ function in double porosity soils

This work analyses the macroscopic definition of Bishop’s χ function for double porosity soils by imposing the thermodynamic consistency of the constitutive stress derived from that function. The analysis presented demonstrates that, under the assumption of equilibrium between macrostructural and microstructural water, χ should be understood, from a thermodynamic perspective, as a correction of the macrostructural suction that enables an accurate definition of the increase in Helmholtz free energy in the soil when using the constitutive stress to compute the strain work. For the low salinity conditions assumed, the proposed functional structure establishes a broad model framework that can accommodate developments tailored to different materials and test conditions.