Experimental study on the effect and influence mechanism of boundary hydraulic pressure on frost heaving

Water supply is one of the dominant factors determining the frost heave, and many researchers have studied the occurrence of frost heaving under the water boundary conditions of no-water supply or no-pressure water supply. Soil freezing is fed by confined groundwater in some cases, however, limited studies have focused on the role of boundary hydraulic pressure. To clarify the effect of boundary hydraulic pressure on soil frost heaving, a series of one-directional soil freezing experiments under various boundary hydraulic pressures were conducted, and the freezing characteristics, pore water pressure (PWP), hydraulic conductivity and the microstructure of unfrozen soil in the longitudinal section were observed and analyzed. The results showed that boundary hydraulic pressure not only increases the frost heave but also inhibits the freezing front from advancing. The increase in boundary hydraulic pressure favors the development of micro-lenticular cryostructure and layered cryostructure. More-over, the total water intake volume and moisture content after tests increase with increasing boundary hydraulic pressure. The increased water content of soil sample and the PWP gradient of frozen fringe account for the increased frost heave. In addition, the results demonstrated that the hydraulic pressure can enhance the permeability of unfrozen zone and frozen fringe. Microscopic analysis showed that hydraulic pressure can promote the pore orientation of longitudinal section of the soil, which transfers from the uniform distribution to the triangular distribution.