Debris flows are a type of natural disaster induced by vegetation-water-soil coupling under external dynamic conditions. Research on the mechanism by which underground plant roots affect the initiation of gulley debris flows is currently limited. To explore this mechanism, we designed 14 groups of controlled field-based simulation experiments. Through monitoring, analysis, calculation, and simulation of the changes in physical parameters, such as volumetric water content, pore-water pressure, and matric suction, during the debris flow initiation process, we revealed that underground plant roots change the pore structure of soil masses. This affects the response time of pore-water pressure to volumetric water content, as well as hydrological processes within soil masses before the initiation of gully debris flows. Underground plant roots increase the peak volumetric water content of rock and soil masses, reduce the rates of increase of volumetric water content and pore-water pressure, and increase the dissipation rate of pore-water pressure. Our results clarify the influence of underground roots on the initiation of gulley debris flows, and also provide support for the initiation warning of gully debris flow. When the peak value of stable volumetric water content is taken as the early warning value, the early warning time of soil with underground plant roots is delayed by 534 to 1253 s. When the stable peak value of pore-water pressure is taken as the early warning value, the early warning time of soil with underground plant roots is delayed by 193 to 1082 s. This study provides a basis for disaster prevention and early warning of gully debris flows in GLP, and also provides ideas and theoretical basis under different vegetation-cover conditions area similar to GLP.

The extent of wildfires in tundra ecosystems has dramatically increased since the turn of the 21st century due to climate change and the resulting amplified Arctic warming. We simultaneously studied the recovery of vegetation, subsurface soil moisture, and active layer thickness (ALT) post-fire in the permafrost-underlain uplands of the Yukon-Kuskokwim Delta in southwestern Alaska to understand the interaction between these factors and their potential implications. We used a space-for-time substitution methodology with 2017 Landsat 8 imagery and synthetic aperture radar products, along with 2016 field data, to analyze tundra recovery trajectories in areas burned from 1953 to 2017. We found that spectral indices describing vegetation greenness and surface albedo in burned areas approached the unburned baseline within a decade post-fire, but ecological succession takes decades. ALT was higher in burned areas compared to unburned areas initially after the fire but negatively correlated with soil moisture. Soil moisture was significantly higher in burned areas than in unburned areas. Water table depth (WTD) was 10 cm shallower in burned areas, consistent with 10 cm of the surface organic layer burned off during fire. Soil moisture and WTD did not recover in the 46 years covered by this study and appear linked to the long recovery time of the organic layer.

Debris flows are destructive mass movements that pose multifaceted challenges with profound social and environmental implications in the Western Himalayas. For precise modeling and flow behavior prediction, it is essential to understand the rheological characteristics of debris flow material. In the current study, rheological characteristics like yield stress and viscosity were determined by a series of lab tests using a parallel plate setup in a rheometer. An optimized sampling approach created the reconstituted soil samples of finer particles to change the solid volume concentration and volumetric water content (w/c). Later, the feature importance of finer particles in debris flow rheology was determined using a machine learning regressor. Non-Newtonian behavior was shown by each composition and was similar to Herschel-Bulkley's rheological model. The eXtreme Gradient Boosting (XGBoost) regression model was developed for rheological parameters with robust model fitting with R2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${R}{2}$$\end{document} = 0.90 for yield stress and R2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${R}{2}$$\end{document} = 0.94 for viscosity. The model helped in understanding the sensitivity of rheological parameters with solid constitutents of debris flows. The findings showed that water content and silt concentration substantially impacted the debris flow's rheology. The yield stress was more dominated by silt followed by fine sand, whereas water content influenced the viscosity more than any solid concentration. The flow behavior was also affected by the distribution of grain sizes, with finer particles exhibiting higher viscosity and shear stress than coarser particles. These results enhance understanding of debris flow rheology and highlight the complex interplay between geohazards and sustainable development.

A capillary barrier cover (CBC) is a geotechnical structure which a coarse-grained soil layer covered by a fine-grained soil layer. A CBC can retain downward water infiltration, increase water storage capacity and lateral diversion, and prevent capillary rise. Geotextiles are usually set up as isolation layers between fine-grained and coarse-grained layers to prevent fine particles entering the coarse-grained layer, resulting in a decrease in downward water infiltration and water storage capacity. However, crustal stress, farming, animal, plant activities, and other factors may cause damage to the isolation layer. At present, there is no reliable and accurate method to determine the location and degree of damage to the isolation layer. The existing methods search for the damage location by excavating the whole fine layer, which incurs high maintenance costs. If the damaged position of the CBC isolation layer can be accurately obtained, it can reduce maintenance costs. Therefore, this study investigated the influence of a coarse-grained layer mixed with different particle sizes and proportions of fine particles on water storage capacity through laboratory soil column experiments. The results are as follows: (1) Fine particle mixing into the coarse-grained layer will reduce water storage capacity, and there is a worse admixture ratio that minimizes water storage capacity. (2) The CBC enhances the fine-grained layer volumetric water content (VWC), but the enhancement degree decreases as the distance from the fine-coarse interface increases. (3) A method has been proposed to determine the location and degree of damage to the isolation layer. When the VWC at the fine-coarse interface reaches a stable level during breakthrough, the CBC effect exists, the higher the VWC at the fine-coarse interface, the stronger the CBC; when the VWC at the fine-coarse interface is unstable during breakthrough, the CBC effect disappears, and the median diameter of the fine particles mixed into the coarse-grained layer is finer than or equal to the fine-grained particles' median diameter.

An enhanced geosynthetic material, PVF-wicking geosynthetic (PWG), was developed to improve the performance of the wicking geosynthetic product family, e.g., the wicking geotextile (WG). The PWG was made by coating deep-grooved wicking yarns and reinforcement with the layered polyvinyl alcohol formaldehyde (PVF) high-absorbent materials. The drainage performance of PWG was assessed through beaker drainage tests and soil column tests. The results of the beaker drainage test and SEM images indicate that PVF does not obstruct the deep-grooved yarns. It is found that, by facilitating efficient water absorption, storage, and transfer as a transit layer between the subgrade and wicking yarns, PVF plays a crucial role in enhancing the drainage capabilities of the geosynthetic material. PWG outperforms WG in terms of drainage efficiency under both static and cyclic loading conditions. The mechanism of the drainage improvement by PWG under cyclic loading is that the excess pore pressure within the PVF layer accelerates the water transfer from the pores of the PVF into the grooves of yarns. PWG, included with reinforcement, exhibited comparable interface characteristics to WG, with the potential to meet the requirements of soil stabilization. The remarkable drainage efficiency of PWG underscores its potential for practical applications.