Frost heave and frost heaving-induced pressure under various restraints and thermal gradients during the coupled thermal–hydro processes in freezing soil

Studies of frost heaving-induced pressure (FHIP) have been gaining increasing attention for applications using the freezing method to strengthen soils. This paper demonstrates a technique for measuring the FHIP when heaving is constrained. A series of freezing tests were conducted under various restrained stiffnesses and associated with a thermal gradient. The evolution of frost heave and the FHIP during coupled hydro–thermal interaction were examined. From this study, it was found that restraint prevents frost heave by impeding formation of the ice lens. A thermal gradient is a necessary condition for both water flow and frost heave, since pore water solidifies into ice and thus causes suction (negative pore water pressure) at the base of the ice lens. The pore structure and flow properties of freezing soil vary, since ice crystals progressively block the flow of water, whilst discontinuous ice lenses result in variation of water distributions. The increase of the FHIP appeared to cease when the ice pressure reached a maximum value, based on the microscopic analysis of equivalent water pressure. Moreover, the stable stage for the FHIP lagged behind the stabilization temperature. A macroscopic analysis of the different FHIPs under various different restraints was also carried out. It was found that increased restrained stiffness caused increased deformation and resulted in an increase of the observed FHIP. The coupled hydro–thermal behaviors analyzed in this study enable a better understanding of heat transfer and fluid flow in freezing granular media (soils).