Study on salt expansion mechanism of subgrade-culvert transition section in saline soils and cold regions

The theory of salt expansion in saline soils is a multi-physics coupling problem, the deformation process of the subgrade-culvert transition section is more complex. This paper proposed a mathematical model to describe the coupled water-thermal-salt-mechanical process in saline soils. Then, experimental studies of water-salt migration and salt expansion under one-way cooling condition were done to verify the correctness of the model. Finally, the numerical model of the subgrade-culvert transition section of the Golmud-Qarhan Highway was established. The results of the calculations show that the water-salt migration laws and salt expansion characteristics of saline soils can be correctly described by the mathematical model, under one-way cooling condition, with a deformation rate of about 3.47% for saline soils with a sulphate salt content of 1.49%. Then, because of the dramatic temperature change around the culvert, a salt accumulation area is created around the culvert during the cold season, which is the main reason for the salt expansion of the subgrade structure. The maximum deformation in the subgrade-culvert transition section occurs close to the road border above the culvert, and the maximum deformation in a freeze-thaw period lags the coldest time of the cold season.