Solid-fluidization transition-induced flow-like events pose significant threats to both ecological systems and human society. This geophysical phenomenon undergoes a continuous and catastrophic solid-fluidization-solid retransition, which often leads to severe disasters. A series of flume and rheological tests were conducted to explore the continuous solid-fluidization-solid retransition mechanism of sedimentary loess. The results showed that the flow distance after phase retransition increased by 39.5% compared with the first flowslip distance. With increasing rainfall intensity, the moisture content during phase transition tended to decrease while the time required for reactivation lengthened. Rheological analyses revealed that the reduction and recovery of storage modulus exhibited by thixotropy is a crucial mechanism in the phase retransition of soil, and they have significant time-concentration dependence. A higher soil water content leads to a longer structural recovery time and stronger thixotropy, which agrees well with the results of flume tests. Our experimental data NSav and NBag showed a positive power-law relationship and had similar fitting coefficients to the field case data, indicating that our experimental results have successfully captured the kinematic and rheological characteristics of real mudflow events. This study suggests that thixotropy can be used to interpret complex phase retransition processes in mudflow and can also help to explain the hypermobility and reactivation of many large geophysical processes, such as pyroclastic flows.

The demand for increased axle loads and speeds of trains can diminish the stability of track substructure, leading to potential particle migration or slurry pumping under critical drainage conditions. This paper primarily focuses on the role of geosynthetics in mitigating the risk of soil fluidization potential under cyclic load. Laboratory experiments were conducted to evaluate the effectiveness of geosynthetics including geotextiles, geocomposites, and prefabricated vertical drains (PVDs). The laboratory study indicates that subgrade instability primarily occurs due to the migration of fines towards the subgrade surface and the substantial increase in moisture content (MC). Dynamic Filtration Tests (DFTs) reveal that geocomposite inclusion in rail tracks can reduce the fluidization potential of soft soils and the combined prefabricated vertical drains-geocomposite system can be used to mitigate the critical excess pore water pressure (EPWP) that accumulates in shallow or deeper soil layer due to activated radial drainage paths.

Extreme rainfall events, within the context of climate change, pose a heightened risk of geohazards to mountainous regions. On 22 June 2022, a rainstorm-induced landslide-mudflow occurred in a terraced field in Longsheng County, Guangxi Zhuang Autonomous Region, China. The disaster began as a rotational slide, and mobilized into a mudflow with high mobility and long runout, causing significant damage to the local community. This event served as a wake-up call not only for the safety of mountain settlements, but also for the protection of terraced fields as Globally Important Agricultural Heritage Systems. To elucidate the trigger and mudflow mobilization of the event, field investigation, hydrological and agricultural analyses, and laboratory tests were conducted. It was found that the persistent and record-breaking rainfall directly triggered the disaster by increasing pore water pressure. The transition from paddy terraces to dry terraces was deduced to have contributed to a lack of maintenance in the terrace drainage system, thereby heightening the likelihood of landslides. The mudflow mobilization was attributed to excess pore water pressure generated by soil contraction and an undrained condition maintained by low permeability soil. Soil experiencing sliding may be more susceptible to shear contraction, consequently resulting in long-runout motion. Under conditions of increasing extreme rainfall, greater attention needs to be paid to geo-disaster prevention and terraced field protection in mountainous regions.

The waterfront sheet -pile wall, retaining the saturated backfill, is susceptible to seismic damage due to the unbalanced forces between the backfill and toefill sides. In light of this concern, three dynamic centrifuge model tests were conducted at Zhejiang University under the framework of LEAP-RPI-2020. The centrifuge models, consisting of a dense layer and an overlying medium -dense layer, were fully saturated and retained by a cantilevered sheet -pile wall. This study aims to elucidate the dynamic responses of this soil -wall system subjected to varying shaking intensities, including acceleration responses, excess pore pressure ratios (r(u)) and shear strains in model soils, ground deformations and wall rotation. The results provide valuable insights into the liquefaction responses of the soil under mild to severe rotation of the sheet -pile wall. The mechanism of flow liquefaction triggered with r(u) < 1 was revealed by cyclic triaxial tests, which is defined as fluidization in this study. It qualitatively explains the phenomenon that the peak r(u) cannot reach unity in the vicinity of sheet -pile wall within the backfill. Furthermore, the efficacy of V-s -based liquefaction characterization model was examined in the saturated backfill, and the discrepancies mainly resulted from (1) the ignorance of fluidization in the traditional liquefaction criteria (i.e., r(u) = 1); and (2) an overestimation of the cyclic shear stresses in soils adjacent to sheet -pile wall.