Investigation on binary medium model taking frozen silt soils under -6℃ for example

The binary medium model (abbreviated as BMM) is suitable for unfrozen geomaterials, such as rock, isotropic or anisotropic structured soils, overconsolidated clay, rockfill materials and loess, and has a good accuracy and satisfactory applicability. Similarly, in order to investigate the stress-strain relationship of frozen soils, the BMM is introduced and employed to simulate the deformation characteristics. Based on the theoretical framework of breakage mechanics for geomaterials and the concept of BMM, the saturated frozen silt soils are conceptualized as the binary medium consisting of bonding blocks with strong bonding (the frozen soil skeleton) and frictional elements without weakened bonding (the melted soil skeleton), and the bonding elements will be crushed, melted and gradually transformed to frictional elements with the increasing confining pressure during the loading process, resulting two of the bonding blocks and weakened bands bear the external loads, collectively. A series of cryogenic triaxial compressive tests are conducted at -6℃ under confining pressure of 0.3 to 15.0 MPa, and the following test results demonstrate that the stress-strain curves behave three varying stages with the increasing axial strain, which are the initial linear elastic stage, elasto-plastic stage and strain softening stage, respectively. The strength of frozen soils increases first and then decreases with the further increase of confining pressures. The critical confining pressure corresponds to the peak strength for different test curves, under which the strain softening phenomenon is less obvious. From a mesoscopic point of view, the deformation and damage mechanisms of frozen soils are investigated based on the concept of binary medium, and the stress-strain formulation is established on the basis of the homogenization theory of the heterogeneous materials. Finally, the evolution of breakage function is analyzed and discussed through determination of the