The stability of geotechnical structures after an earthquake is primarily determined by the residual strength of surrounding soils that have not fully liquefied. This research employs the discrete element method (DEM) to study the undrained post-cyclic shear behaviour of sand under triaxial conditions, focusing on the effect of varying degrees of liquefaction (LD) simulated by subjecting the samples to different lengths of cyclic loading. Different types of cyclic loading, i.e. symmetric (fully reversal), partially reversal, and non-reversal ones, as well as the effect of sample density, have been considered. The results indicate that the samples under fully or partially reversal cyclic loading eventually liquefied, displaying a cyclic mobility failure mode. In contrast, samples under non-reversal cyclic loading develop plastic strain accumulation (PSA) failure without liquefaction. The post-cyclic shear stiffness of the samples is affected by both LD and the type of cyclic loading. For samples under reversal cyclic loading, the post-cyclic shear stiffness decreases as LD increases. Notably, the liquefied samples (LD = 1) initially exhibit near-zero stiffness during post-liquefaction shear until highly anisotropic force chains are formed along the loading direction, with their buckling leading to stiffness recovery. The length of the low-stiffness stage is influenced by the static shear stress and the relative density of the sample, which determines the rate of anisotropy accumulation during cyclic loading. The onset and completion of stiffness recovery are marked by a peak in anisotropy and an abrupt increase in effective anisotropy, respectively. For samples under non-reversal cyclic loading, the post-cyclic shear stiffness initially decreases with the increase in LD but increases at higher LDs due to the significant anisotropy developed during the cyclic loading stage.

Low-saturation liquid-containing granular materials are commonly encountered in both natural and industrial settings, where interstitial liquids significantly affect the motion of particles, while particle size polydispersity plays a crucial role in determining the level of system cohesion. In this study, the collapse of wet polydisperse granular columns is numerically investigated based on the developed discrete element model, with corresponding dam-break experiments performed to validate our numerical model and methodology. The dependence of the dynamics and flow mobility on particle size distribution is primarily examined, and the underlying mechanisms are also explored by analyzing particle path lengths and average fidelity. Building upon the effective Bond number proposed using the mixing theory, a macroscopic cohesion parameter at the material scale is defined by considering the dependence of the collapse on the system size effect. The relevance of this cohesion parameter in describing different wet polydisperse granular collapses is further validated based on our designed experimental tests and DEM simulations. The approach of constructing the cohesion parameters at different scales can be extended to characterize cohesion effects in more complex wet polydisperse granular flows and describe their associated rheological behaviors.

The deep-sea mining machine is a crucial component of the seabed mining system. However, due to the unique mechanical properties of deep-sea sediments, the machine often encounters problems like slipping and sinking during operation. Traditional model testing struggles to analyze the interaction between tracks and soil on a microscopic level. This study uses an MBD-DEM coupling method to simulate track-soil interactions, revealing the impact of grouser shape, spacing, track plate spacing, ground pressure, and pretension on the machine's performance. The results show that the grouser causes the most soil disturbance when entering and exiting the soil, providing significant traction during entry, though some grousers face resistance while moving. Increasing grouser spacing initially boosts traction but later decreases it, as too small or too large spacing affects thrust and soil utilization. Enlarging track plate spacing reduces motion resistance and increases traction. Raising ground pressure also enhances traction but increases soil disturbance. Setting pretension to 12% of the machine's weight results in smoother operation. Additionally, the study considered the impact of biomimetic grousers on traction under multi-grouser conditions and designed more efficient grousers, providing theoretical guidance for the structural design of deep-sea mining machine tracks.

Landslide mobility refers to how far and fast a landslide can move downslope. It controls landslide impact areas and damage power. Highly mobile landslides are often initiated on slopes steeper than 30 degrees. However, on 18 December 2023, an earthquake-induced landslide (35 degrees 52 ' 54 '' N, 102 degrees 51 ' 10 '' E) exhibited extraordinary mobility, with an overall travel angle of 1.5 degrees, breaking an on-land landslide record. The landslide originated on a gentle slope (3.6 degrees), eroded an earth dam along its travel path, and finally destroyed 51 houses and claimed 20 lives. Remote sensing and field surveys were conducted to provide morphological characteristics of the hazard chain. A numerical program, EDDA (Erosion-Deposition Debris Flow Analysis), was employed to reproduce the flow dynamics and investigate the causes of hypermobility. The findings reveal three primary causes of hypermobility: (1) liquefaction of the saturated silty loess stratum due to the combined effects of irrigation activity and seismic loading, (2) the loose and macro-pore structure of loess, and (3) confined topography and icy channel bed. The mechanisms revealed have broad implications for understanding fluidized mass movements on gentle slopes in seismically active regions.

Rock-ice avalanches have frequently occurred in the Eastern Himalayan Syntaxis region due to climate change and active tectonic movements. These events commonly trigger catastrophic geohazard chains, including debris flows, river blockages, and floods. This study focuses on the Zelongnong Basin, analyzing the geomorphic and dynamic characteristics of high-altitude disasters. The basin exhibits typical vertical zonation, with disaster sources initiating at elevations exceeding 4000 m and runout distances reaching up to 10 km. The disaster chain movement involves complex dynamic effects, including impact disintegration, soil-rock mixture arching, dynamic erosion, and debris deposition, enhancing understanding of the flow behavior and dynamic characteristics of rock-ice avalanches. The presence of ice significantly increases mobility due to lubrication and frictional melting. In the disaster event of September 10, 2020, the maximum flow velocity and thickness reached 40 m/s and 43 m, respectively. Furthermore, continuous deformation of the Zelongnong glacier moraine was observed, with maximum cumulative deformations of 44.68 m in the distance direction and 25.96 m in the azimuth direction from March 25, 2022, to August 25, 2022. In the future, the risk of rock-ice avalanches in the Eastern Himalayan Syntaxis region will remain extremely high, necessitating a focus on early warning and risk mitigation strategies for such basin disasters.

Purpose The aim of this study was to evaluate the toxic potential of mining residues by 1) evaluating the concentrations of heavy metals and arsenic in soil and earthworm's samples from impacted and reference sites in Charcas and Villa de la Paz, San Luis Potos & iacute;, M & eacute;xico; and 2) evaluating effects by laboratory bioassays and the comet assay in the earthworm Eisenia andrei. Methods The quantification of metals in soils was carried out by the Thermo Scientific Niton XL3t Gold Serie 500 environmental analyzer for X-ray fluorescence (XRF), and in the earthworm tissue through ICP-MS. The evaluation of the genotoxic potential of soils was assessed through movility and exposure bioassays with earthworms, determining DNA damage using the comet assay at the end of the bioassays. Results In Charcas, the concentrations in soils of heavy metals from highest to lowest were: Pb > Cu > Mn > Cd (Impacted); and Mn > Pb (Reference). In Villa de la Paz, the concentrations were: As > Mn > Cu > Pb (Impacted) and Mn > Pb > As (Reference). The exposure pattern to heavy metals in earthworms in Charcas was: Pb > As (Impacted and Reference); and in Villa de la Paz it was: As > Mn > Pb > Cu > Cd (Impacted), y Pb > As (Reference). In both mining districts, the magnitude of DNA damage in earthworms was: Impacted > Reference > Control. Conclusion The results indicate that the impacted soils of both sites represent a significant source of exposure to edaphic organisms, with a notable genotoxic potential.

The assessment of landslide susceptibility often overlooks the influence of forests on shallow landslide mobility, despite its significance. This study delved into the impact of forest presence on shallow landslide mobility during intense rainfall in Mengdong, China. Field investigations were coupled with the analysis of pre- and post-rainfall remote sensing (RS) images to delineate landslides. The ratio of landslide height (H) to travel distance (L) from a digital elevation model (DEM) were used to calculate landslides mobility. Preceding the event, forest coverage was evaluated using the normalized difference vegetation index (NDVI) derived from multiband RS image. The research identified 1531 shallow landslides in the area, revealing a higher concentration of landslides on slopes with elevated NDVI. Results indicated that disparities in soil permeability and cohesion, generating pore water pressure (PWP), triggered clusters of shallow landslides. Shallow landslides exhibit a higher propensity on slopes with elevated NDVI. The dimensions (height and area) of these identified shallow landslides typically exhibit a positive correlation with NDVI, consequently resulting in longer travel distances for landslides occurring on higher NDVI slopes. The average H/L ratio of all identified landslides was about 0.63. H/L generally increases with NDVI and decreases with landslide area. However, due to river channel restrictions, the H/L increases with slope gradient. The findings suggest that the high permeability of areas with tree roots poses a risk to the shallow stability of slopes, yet trees contribute to mitigating landslide mobility.

In this study, constitutive behavior of granular soils is modeled through a generalized plasticity-based theoretical framework. The soil hardening is addressed by a novel relationship proposed to calculate plastic strains and their evolution during loading history. The model is effective in predicting the response and incorporating it into a numerical scheme. Focus is given to stress ratios yielding liquefaction in a few stress cycles. The proposed hardening law is based upon a combined deviatoric-volumetric hardening rule updating the stress-strain relationship and plastic strain vector. Numerous undrained monotonic and cyclic triaxial tests are simulated for verification of the constitutive formulation. Results indicate that the developed model for sand-like cohesionless soils proves to match fairly well with the available experimental data. Plastic strains are calculated accurately and accumulated pore pressures are well captured. Triaxial test simulations exhibit a successfully improved way of capturing the essential static and cyclic behavior of granular soils.