Accumulative plastic strain behaviors and microscopic structural characters of artificially freeze-thaw soft clay under dynamic cyclic loading

The artificial ground freezing (AGF) technique has been extensively employed in the construction of underground structures. Due to the existence of freeze-thaw cycle in the AGF technique, the properties of soft clay deteriorate and thus larger settlement is induced during its later operation phase. To investigate the strain behaviors of the soft clay undergoing freeze-thaw cycle and discuss the differences between the soft clay undergoing and without undergoing freeze-thaw cycle under dynamic cyclic loading, a series of dynamic triaxial tests with consideration of different influencing factors as dynamic stress amplitudes, freezing temperatures, and freezing temperatures were conducted. Based on the experimental data, an empirical model for predicting the accumulative plastic strain was proposed and validated. Besides, the microscopic structural characters of the artificially freeze-thaw soft clay were explored via mercury intrusion porosimetry (MIP) tests. The results show that the total accumulative plastic strain of specimens increases with the increase of the dynamic stress amplitude, while decrease with the increase of the loading frequency. The specimens undergoing freeze-thaw cycle produces larger plastic strain, and the lower the freezing temperature is, the larger the total accumulative plastic strain is. The empirical accumulative plastic strain model, which can synthetically reflect the effects of dynamic stress amplitudes, loading frequencies, freezing temperatures and number of cyclic loading is proposed and validated. The freeze-thaw cycle has a significant effect on the strain behavior of soft clay in a way decreasing the pore volume and increasing the pore size of the specimens. Results obtained in this paper may provide meaningful references for studying the deformation characteristics of the soft clay in engineering applications.