Deformation and Failure Mechanisms of Weak Interlayer-Controlled Landslides: A Case Study of the Zhoujia Landslide in Western China

Weak interlayers within slopes exhibit poor physical and mechanical properties and are prone to degrade into slip zones, consequently impacting stability. This paper takes the Zhoujia landslide in the middle reaches of the Yalong River as a case study. Through field geological investigations, the landslide body of the Zhoujia landslide was divided into deformation Zone B1 (penetrated by a weak interlayer) and non-deformation Zone A. Using barite powder, quartz sand, and iron powder as aggregates and adding bentonite and paraffin liquid to prepare similar materials, a base friction test was carried out. The velocity vector analysis was performed using PIVlab software. Finally, the deformation and failure mechanism of a weak interlayer-controlled landslide was investigated through discrete element PFC numerical simulation. The research results indicate that deformation Zone B1 in the slope model is controlled by the weak interlayer. In the base friction test, the deformation and failure process of the slope can be divided into four stages: the microcrack development stage, the critical block detachment stage, the crack extension stage, and the complete failure stage, with a slip‒pull failure mode. The numerical simulation results indicate that there are significant differences in deformation between Area A and Area B1. The cumulative displacement in Area A is approximately 6–10 mm, showing a converging trend; whereas, the cumulative displacement in Area B1 is approximately 50–280 mm and continues to increase. The deformation in Area B1 is greater than that in Area A. If Zone B1 experiences further instability, it may experience traction-type deformation and failure of the entire slope.