Fatigue fracturing of Malan loess and its implications to loess toppling failure

Abstract

High and steep slopes are common in loess-covered regions due to the prevalent hilly terrain. Recently, toppling failures of these slopes have increased, largely driven by the frequent occurrence of extreme climate events. Loess toppling involves Mode I fracturing (cracking) behind detaching blocks, which can be triggered by static or cyclic loading. However, the mechanisms by which cyclic loading induces fatigue fracturing and crack propagation, ultimately promoting loess slope toppling, remain poorly understood. This study employed Mode I fracturing experiments and numerical simulations to investigate the fatigue fracturing behavior of undisturbed loess under cyclic loading. A numerical simulation scheme was developed by integrating a corrosion algorithm with the built-in linear parallel bond model, enabling the analysis of progressive damage. The results demonstrate that loess exhibits strain-softening behavior and develops fatigue fracturing and crack propagation under cyclic loading. Cyclic loading significantly reduces fracture toughness compared to static loading (a decrease exceeding 80 % was observed after 1000 loading cycles). Increasing water content diminishes the efficiency of loading cycles in reducing fracture toughness. The load–displacement curves display hysteretic behavior, and the accumulation of irreversible deformation progresses from slow to fast development towards fatigue fracturing with increasing cycles. Post-fatigue failure may manifest in brittle or ductile modes, depending on the accumulated irreversible deformation. This deformation is linked to the weakening or breakage of interparticle bonds caused by tensile stress concentration around the crack tip. These findings identify fatigue fracturing as one of the key mechanisms driving loess crack propagation and subsequent toppling failure. Consequently, natural conditions conducive to fatigue failure, such as micro-vibrations, temperature variations, and humidity, should be considered when identifying potential toppling sites in loess areas.