Assessing the influence of non-plastic fines on rainfall-induced landslide initiation and propagation: Flume test findings.

Numerous fluidized landslides with long runout distances and fast movements have been triggered by heavy rainfall under climate change. Non-plastic fines are frequently involved in many fluidized landslides. However, the role of fines in the initiation and movement of landslides has not been well understood. This study aimed to investigate the role of non-plastic fines in the initiation and movement of rainfall-induced landslides in a flume test setup. The experiments were conducted using mixtures of silica sand (D 50 = 0.16 mm) with different non-plastic fines (D 50 = 0.035 mm) content under different initial densities. The results demonstrated that the behavior of landsliding greatly depends on fines content (FC) and initial packing density (presented by density index, I d) of the soil layers in the flume. The landsliding phenomena could be classified into five failure modes, including slow and fast retrogressive individual sliding, sudden multiple sliding, and deep-seated and shallow fluidized sliding. As the FC increased or I d decreased, the landsliding behavior gradually evolved from slow retrogressive individual sliding to shallow fluidized sliding. For the tests with I d ≥ −0.06, the peak velocity (V p) of the landsliding increased continuously with FC. Conversely, for the tests with I d ≤ −0.19, an optimal FC of 30 % was identified at which V p reached its maximum. Additionally, for FC ≤ 10 %, V p decreased with the increasing I d , while for FC ≥ 20 %, an optional I d existed at which V p reached its maximum for a given FC, and the value of optimal I d (−0.2 ∼ −0.04) varied with FC (20 % ∼ 40 %). The peak pore-water pressure (PWP) (u p) generally increased with the increase of FC. Furthermore, an optimal I d existed at which the PWP built up after landsliding occurrence (Δu) reached its maximum. The equivalent intergranular void ratio (e s *) and equivalent interfine void ratio (e f *), which are calculated by considering both FC and void ratio, are found to be appropriate indices for evaluating and explaining the role of fines in the observed landsliding behavior. In conclusion, the addition of non-plastic fines can change the structure of test materials and result in different failure modes and mobility of landslides by affecting both interparticle contacts and PWP responses. These findings provide insights into the mechanisms of landsliding behavior and have implications for the assessment and mitigation of landslides in geotechnical engineering. • Systematically studied the role of non-plastic fines in the initiation and movement of landslides in the 25 flume tests. • The fines content (FC) and initial density (density index, I d) jointly regulate the landsliding modes and mobility. • Peak PWP (u p) becomes greater in general with FC increasing. Optimal I d existed where PWP built up (Δu) reached the maximum. • We used equivalent intergranular void ratio (e s *) and equivalent interfine void ratio (e f *) to explain landsliding behavior. • The addition of fines could affect landslide modes and mobility by influencing both interparticle contacts and PWP responses. [ABSTRACT FROM AUTHOR]