Evolution of Mechanical Behaviors and Microstructure of Tianjin Binhai Cohesive Soil during Freeze-Thaw Cycles

Abstract

The variation of soil structure and mechanical damage caused by freeze-thaw cycles results in degradation of engineering properties and engineering geological problems, such as deformation, cracking, and even project accidents. In this study, the freeze-thaw cycle tests, unconfined compressive strength tests, scanning electron microscope (SEM) tests, and nuclear magnetic resonance (NMR) tests were carried out to find out the effects of freeze-thaw cycles on the mechanical behaviors and microstructure properties of Tianjin Binhai cohesive soil. The results show that the original structure of the cohesive soil has been destroyed after the first freeze-thaw cycle, resulting in severe loss of compressive strength by 84.2%. The axial stress-strain response showed a strain-hardening behavior transitioned to a strain-softening behavior after 15 freeze-thaw cycles. The unconfined compressive pressure, sensitivity, and void ratio showed the same corresponding reaction with the increase of freeze-thaw cycles. The effects of freezing and thawing on void ratio were weakening with the increase of consolidation pressure, since the void expansion and contraction were limited with smaller void sizes. The frost-heaving force during the freezing process increased the compaction of the soil structure, and face to face contact became the main contact formation, which led to a reduction in void ratio. This study provides technical guidance for evaluation on the mechanical properties and engineering stability of cohesive soil in seasonally frozen areas and technical support for artificial ground freezing treatment on underground construction of the west coast of Bohai Bay.