Formation Mechanism and Deformation Characteristics of Cut Layer Rock Landslide in Island Permafrost Region

Abstract

The Bei’an to Heihe Expressway in China’s Heilongjiang province has been built by widening an existing second-class highway. These widening efforts have been hindered by the location of the old road, as some sections of the subgrade to be widened traverse the Lesser Khingan Mountains. These sections are located in an island permafrost region and experience landslides, which are influenced by the landform, geological conditions, rainfall, and freeze/thaw cycle and remain unstable. In this study, we investigated the K177 landslide site of the Bei’an to Heihe Expressway. We conducted geological surveys, topographic mappings, and geological explorations of the area, and performed field monitoring, indoor tests, and theoretical analyses to study the formation mechanism and deformation characteristics of the landslide. It was concluded that the rupture surface of the landslide is located in completely weathered mudstone. Further, atmospheric precipitation, snowmelt water, and water from the thawing seasonally frozen soil act as continuous water sources for the landslide. Surface water and ground water replenish the Cretaceous pore water through infiltration. Lateral runoff through the surface causes thermal shrinkage cracks in the shallow, high-permeability layer of rock and soil. Low-permeability mudstone with a loose structure forms an aquiclude, while completely weathered mudstone above the aquiclude, which is influenced by the Cretaceous pore water, softens and forms the rupture surface. Hence, landslide movement is affected by changes in slope moisture and the groundwater level, with the landslide exhibiting a low angle and intermittent creep.