Mechanism of strength degradation of frozen soil–rock mixture under temperature rise‐induced particle ice film ablation

The mesoscale effect of climate change and engineering activities on a superficial frozen soil–rock mixture (FSRM) in regions is complex. The decrease in strength caused by particle ice film ablation under temperature rise has various effects, such as upper subgrade settlement deformation. However, the internal mechanism of FSRM strength degradation remains unclear. Triaxial and nuclear magnetic resonance tests on FSRM were performed at various temperatures to clarify the mechanism of FSRM internal degradation. The results show that the strength, cohesion, and internal friction angle of FSRM decrease with increasing temperature, and the attenuation is significant in the range of −5 to 0°C. The change in ice–water content can be divided into three stages (i.e., freezing, phase transformation, and complete melting). In the three stages, the maximum free water is only 24%, while the maximum bound water is 100% above 0°C. Based on the microscopic test results, a mesoscopic calculation model for FSRM particles was developed. It was found that the work between particles is consistent with the law of strength degradation, and the friction function by particles gradually changes to bite work with increasing temperature. By introducing the strain energy theory, the strain energy generated by particle shear work is considered the key index to reflect FSRM strength. The particle ice film locking effect is weakened under temperature rise, and the increase in water weakens the strain energy generated by the work of the bite friction between particles during the shear process. At the macro level, the strength of FSRM deteriorates.