Development and application of the unidirectional freezing -thawing test device under the “open -system conditions”

The effect of freezing and melting in the seasonal frozen soil area is significant. It may cause various degrees of freezing damage to the structure of this area, especially serious for the areas where groundwater water is shallow. Therefore, it is of great scientific significance and engineering value to develop a system which can simulate the unidirectional freezing -thawing process under different groundwater levels with large -scale models. The freezing -thawing system consists of a box structure, refrigeration/heat system, boundary temperature control system, power supply system, groundwater recharge system, thermal insulation system and measurement system. The box structure is made of 6 mm thick steel plate material. The refrigeration/heat system is mainly composed of a semiconductor cooling sheet based on the Peltier effect to achieve refrigeration/heat. The boundary temperature control system mainly relies on the electronic temperature controller for temperature control. The groundwater recharge system mainly uses the modified Mariotte bottle for groundwater recharge. The thermal insulation system mainly adopts a V0 -grade rubber and plastic insulation board. The measuring system can be combined freely according to the purpose of the test. Using this experimental device, the unidirectional freezing and thawing process of large size silty clay samples under groundwater depths of 80 cm and 40 cm is carried out. The test results show that in the process of freezing and thawing settlement, the change rate of temperature is inversely proportional to the distance between the soil layer and the refrigeration/heating plate. The migration of the freezing front can be divided into two stages. The change in water content in the freezing process can be divided into two stages: rapid and slow. The change in frost heaving can be divided into two stages, and the change in the thawing settlement can be divided into three stages. The test results for temperature, moisture content, frozen front and freezing -thawing change also show the reliability of the test device. This device can provide a reference for the development of equipment that can simulate unidirectional freezing -thawing under the open conditions for large -scale models.