Practical model of deformation prediction in soft clay after artificial ground freezing under subway low-level cyclic loading

Settlement was investigated after the long-term operation of a subway system, particularly at segments where the artificial ground freezing (AGF) method was applied in the soft clay area. In this paper, five group soil samples under different freezing temperatures (−5 °C, −10 °C, −15 °C, −20 °C, and −30 °C, respectively) were prepared to simulate different locations perpendicular to freeze tubes during one AGF circulation. Including one group of undisturbed soils, cyclic tri-axial tests were conducted on all samples, and the dynamic strains were measured and analyzed. The results show that the residual cumulative plastic strain of soft clay after artificial freeze-thaw under subway low-level repeated cyclic loading behaves quite differently from the typical Monismith's power function development. A hyperbolic model of cumulative plastic strain of soft clay after artificial freeze-thaw is established and the relevant model parameters has been discussed for practical prediction. A critical cyclic stress ratio (CSR) of soft soil can be empirically calculated out by this practical model, only based on soil stress and soil physical state parameters without numerous cyclic tri-axial tests. All the results could provide significant reference for the safe control and environmental protection during AGF construction and subsequent subway operation.