Abstract: Determination of the freezing pressure in deep alluvium is crucial in designing the outer shaft lining. Using the UMAT of ABAQUS subroutine, the modified Nishihara model for creep of frozen soil is implemented into ABAQUS. With considering the effect of thermo-mechanical coupling during freezing, the freezing pressure distribution of frozen soil before excavation is obtained. Based on these results, the variation of freezing pressure on the outer shaft lining is determined by analyzing the process of deep frozen shaft construction. The results show that the values of freezing pressure are related to the soil depth, soil frost heave ratio and the temperature of the frozen wall. The freezing pressure increases 21% when the depth increases from 400 m to 500 m, and decreases 10% when the average temperature of frozen wall decreases from -16 ℃ to -18℃, and increases 3.8% when the frost heave ratio increases from 2% to 3%. The freezing pressure increases with the increase of depth and frost heave ratio of soil. The lower temperature of the frozen wall benefits the stabilization of the frozen wall. The error between numerical and measured results is less than 15%, showing that the proposed method can reasonably predict freezing pressure of deep shaft in practice.

Key words: modified Nishihara model, deep frozen shaft, frost heave, creep of frozen soil, freezing pressure