Mechanical properties of rooted soil under freeze–thaw cycles and extended binary medium constitutive model

In seasonally frozen soil, soil sometimes is affected by freeze–thaw cycles and root systems. In order to study its mechanical characteristics, a series of consolidation drained triaxial tests under different confining pressures (25, 50, 100, 200 kPa), different freeze–thaw cycles (N = 0, 1, 5, 15) and different root-containing conditions (r = 0, 1, 3) were carried out. The test results show that the specimens exhibit strain softening behavior and volumetric dilatancy phenomena and shear failure under lower confining pressure, and strain hardening and volumetric contraction, bulging failure under higher confining pressure. With the increase of freeze–thaw cycles, the bearing capacity of the sample decreases and the volume strain increases. With the increase of volume ration of roots in the sample, the bearing capacity increases and the volume strain decreases. Based on the binary medium model, the soil is abstracted into bonded elements and frictional elements. At the same time, the bonded elements are transformed into frictional element when the bonded elements are broken during the loading process. Also, the root is abstracted into another non-destructive bonded elements material, which bears the load together. The linear elastic constitutive model is used for root and bonded elements, and the double-hardening model is used for friction elements. Considering the influence of freeze–thaw cycles, the extended binary model is derived here. Finally, the experimental results show that the predicted results of this model are in good agreement with the experimental results, and the new model can relatively well simulate the strain softening and volumetric dilatancy phenomena.