Abstract: Mechanical properties of soft soil will change under freeze-thaw cycle with a certain confining pressure in artificial freezing engineering in coastal soft soil area. Therefore, it is of a great significance to study the influence of freeze-thaw cycle under different confining pressures on the mechanical properties of soft soil. This paper takes the typical muddy soil in Tianjin coastal area as the research object. Through a self-improved temperature controlled triaxial apparatus, the differences of mechanical properties of soft soil under conventional freeze-thaw without confining pressure and freeze-thaw with confining pressure are compared and analyzed. Furthermore, the effects of freezing temperature, number of freeze-thaw cycles and freezing-thawing confining pressure on excess pore pressure, stress-strain characteristics, strength and deformation index of soft soil are revealed. The influence mechanism of freeze-thaw confining pressure on the mechanical properties is explored by SEM. Then, the relationship of shear strength, reduction coefficient of elastic modulus of muddy soil and above influence factors is established by using an exponential function. The results show that the freezing and thawing confining pressure reduces the size and number of pores in the soil after freezing and thawing, which can weaken the damage of freezing and thawing to the soil structure to a certain extent. However, the freeze-thaw confining pressure has little effect on the stress-strain curve. With the decrease of freezing temperature and the increase of the number of freeze-thaw cycles, the strength and moduli of soil are greatly reduced. With the increase of freezing-thawing confining pressure, the freezing temperature and the decrease of the number of freeze-thaw cycles, the excess pore pressure decreases.

Key words: freezing-thawing confining pressure, freeze-thaw cycles, stress-strain characteristics, freezing temperature