Investigating the frost cracking mechanism and the related shallow alpine rockfall initiation process using three-dimensional FDEM

Abstract

Frost weathering plays a critical role in rockwall instability in alpine environments. This paper offers a new insight into the shallow alpine rockfall mechanism from the frost cracking perspective. A numerical framework based on the three-dimensional (3D) combined finite discrete element method (FDEM) is developed to simulate the cryogenic thermal-mechanical coupled processes in cold regions (e.g., water-ice phase change, ice-rock interaction, and frost cracking). Specifically, a new volume expansion model is introduced, allowing for explicit ice-rock interaction in pre-existing cracks while implicit frost heaving pressure in pores or newly generated cracks, to improve numerical efficiency and stability. This framework is validated against benchmark tests and further applied to explore the shallow alpine rockfall mechanism under repeated freeze-thaw cycles. Results suggest that the proposed method effectively simulates temperature field evolution and frost cracking process in cold regions. Frost crack initiation, propagation, and connection with pre-existing cracks, driven by ice-rock interaction in cold seasons, deteriorate structure stability and prepare/trigger shallow rockfall. This study enriches the shallow rockfall mechanism from fracture mechanics standpoint, which is essential for assessing, predicting, and mitigating rockfall activity, particularly in the context of global climate change.