Experimental Study on the Fracture and Failure of the Locking Section of Rock Slopes Caused by Freeze–Thaw of Fracture Water

In rock slopes with a three-section landslide, the locking section is the key control factor. This study conducted double-sided freeze–thaw tests on a scale model of a rock slope with a three-section landslide in a cold region. We monitored the changes in frost heave force, strain, and fracture during the water–ice phase change and investigated the effect of the trailing edge tensile crack length on the frost heave fracture of the locking section. A crack frost heave model was proposed based on rock and fracture mechanics to explore the mechanism of slope crack freeze–thaw weathering. According to the results, the slope shoulder froze first, with the freezing front progressing from the slope shoulder to the interior of the rock mass. The fracture failure in the three-section rock slopes was mostly caused by the frost heave of the trailing-edge tensile cracks. The largest frost heave force and locking section deformation occurred when the temperature of the top of the trailing edge tensile crack decreased from −3.5 °C to −6 °C (whereas that of the bottom of the crack dropped from 0 °C to −2.6 °C). Additionally, the results demonstrate that the frost heave force is positively correlated with the length of the trailing edge tension crack, and shear marks are virtually absent on the tensile fracture surface.