Particle breakage behavior in frozen sands during triaxial shear tests based on the energy principle

It is well known that particle breakage in frozen sands continues throughout the triaxial shearing process and is accompanied by irreversible energy dissipation. Accordingly, it is extremely meaningful to investigate the particle breakage characteristics of frozen sands from the perspective of energy dissipation. First, the contact relationships between particles in frozen sands were abstracted as point-to-point and point-to-surface contacts to determine the mechanism of particle breakage under a low stress state. The extra work or energy dissipation attributed to particle breakage results in a higher friction angle, whereas particle breakage suppresses the occurrence of dilatancy, resulting in a lower friction angle. Thus, the friction angle in the samples was continuously modified during testing to incorporate the comprehensive influence of particle breakage and dilatancy. In this study, a modified energy equation for frozen sands was developed considering the continuous variation in the internal friction angle during the loading process. According to this energy equation, the calculated energy dissipation of crushing during shearing is always greater than zero due to the irreversible crushing behavior and increases gradually until it reaches a stable value when no crushing occurs. Finally, a series of cryogenic triaxial compression tests at various temperatures and confining pressures were performed to systematically explore the particle breakage behaviors of frozen soil by using an improved apparatus, and the energy dissipation of frozen soils during the crushing process was further calculated and analyzed based on the improved energy equation. The results demonstrate that the degree of particle breakage is most severe when the axial strain ranges from 1.5% to 2.5% and that energy dissipation presents a hyperbolic trend with axial strain. The results also imply that the particle breakage energy consumption increases when the soil samples are subject to a higher confining pressure, higher shear stress or lower temperature. The aim of this research is to provide a theoretical basis for establishing suitable constitutive models for frozen soils by considering particle breakage from the perspective of energy dissipation.