Micromechanics-based binary-medium constitutive model for frozen soil considering the influence of coarse-grained contents and freeze-thaw cycles

In cold regions, the deformation characteristics of frozen soils with different coarse-grained contents change significantly under the freeze-thaw (F-T) cycles. A series of cryogenic triaxial compression tests were conducted to investigate the deformation characteristics of frozen soil at -10 degrees C experiencing freeze-thaw cycles. The results indicated that the stress-strain response is nonlinear, elastoplastic accompanied by strain hardening, and volumetric compaction followed by dilatancy for a given coarse-grained content and F-T cycle. To reveal the aforementioned mechanisms, a micromechanics-based binary-medium constitutive model combining the breakage mechanics for geomaterials theory and the homogenization method is proposed. The following salient features of the proposed model in terms of micro-meso-macro scales are summarized: (i) The frozen soil is idealized as a representative volume element (RVE) at the macroscale, which is composed of elastic bonded elements and elastoplastic frictional elements at the mesoscale. The meso-macro upscaling process for frozen soil is described as the binary-medium constitutive. Furthermore, the Mori-Tanaka method is employed to describe the non-uniform deformation between macro-RVE and mesoscale bonded elements in frozen soil. (ii) At the microscale, the micro-meso upscaling process of the bonded elements is performed by employing the homogenization method which allows for considering the ice cementation breakage and the influence of coarse-grained contents. Meanwhile, for the frictional element, considering the microplastic deformation is related to the frictional sliding mechanism, a Drucker-Prager yield criterion and a non-associate flow rule based on the homogenization approach are proposed. Finally, the developed micromechanics-based binary-medium constitutive model can describe the deformation mechanism of frozen soil from both micro- to meso-scale and from meso- to macro-scale simultaneously, and the deformation of frozen soil with different coarse-grained contents under different F-T cycles is well predicted.