Increasing rain levels can easily destabilize and destroy particulate matter in mountainous areas, which can cause natural disasters, such as debris flow and landslides. Constitutive equations and numerical simulation are the theoretical bases for understanding the behavior of these disasters. Thus, this study aimed to investigate the impact of the debris flow and its entrainment behavior on gully bed sediments. We adopted a coupled analysis method based on elastic–plastic constitutive equations by considering the elasto-plasticity of slurry and the elastic characteristics of debris materials. The coupled method consisted of smooth particle hydrodynamic (SPH), discrete element method (DEM), and finite element method (FEM) (SPH–DEM–FEM). SPH particles represented fluid, DEM particles denoted solid immersed in fluid, and FEM elements represented the terrain and structures. The coupling analysis model was used to simulate the coupling contact of solid, liquid, and structures and to describe the entrainment behavior between solid and liquid phases. The model feasibility was verified by comparing the basic simulation results with experimental values of the dam break model and the rotating cylindrical tank model. The coupled model was then combined with the data management and modeling of geographic information system to simulate the 2010 Yohutagawa debris flow event. Finally, we explored the influence of debris shape-related parameters on the debris flow erosion entrainment process.

Although vegetation is increasingly used to mitigate landslide risks, how vegetation roots affect the landslide threshold of slope has rarely been explored, particularly in the case of lateral runoff. In this study, we established a two-dimensional saturated-unsaturated infiltration equation considering the hydraulic effects of vegetation roots. The analytical solution for the shallow unsaturated two-dimensional coupled infiltration of vegetated slope (VS) was obtained by a Fourier transform technique. The numerical method was used to evaluate the stability of VS caused by four root architectures, the rainfall amount, and the rainfall duration. Subsequently, the transformation law in runoff, vegetation evaporation, and landslide threshold was analyzed. The results indicate that the factor of safety (FOS) increases with increasing drying time and decreases with increasing depth; the minimum FOS is at the junction of the root-rootless zone. Runoff and vegetation evaporation are favorable for the shallow stability of VS. The time of the safe area is 35 h for rainfall amount 500 m in the uniformly root clay slope. Moreover, four landslide threshold curves that reflected the root architecture, rainfall amount, and rainfall duration are developed, which are more realistic than those created using one-dimensional instability modeling.

Coal measure soils are the main component in the slip zones of landslides along the Changli highway in China. Therefore, exploring the residual strength of coal measure soil affected by dry-wet cycling is helpful for evaluating landslides. However, very few researchers have reported on the residual strength behavior of coal measure soil subjected to dry-wet cycling. In this study, we performed three tests (ring shear test, scanning electron microscopy test, and mercury intrusion porosimetry test) to evaluate the residual strength behavior of coal measure soil under different dry-wet cycles. Our results indicated that the peak strength decreased with increasing dry-wet numbers and that dry-wet cycling had no evident effect on the residual strength. Moreover, the residual strength in the slip soil was approximately proportional to the normal stress. Furthermore, the degeneration of peak cohesion exponentially increased, and the porosity and fractal diameter also increased with the dry-wet numbers. The connection between mineral particles changed from a stable layered structure to an unstable chain structure. Consequently, we inferred the failure mechanism of K213-type shallow landslides and formulated appropriate preventive measures. This study is of great significance for understanding the mechanical behavior of the slip zone of coal measure soil and predicting the re-emergence of coal measure soil landslides.

Strength of vegetated coal-bearing soil is of great significance to evaluate the shallow stability of vegetated slopes in coal-bearing soil regions. This paper takes D-W cycles, dry density, water content, and vegetation root (VR) content as four factors and carries out the triaxial test for the orthogonal design of vegetated coal-bearing soil in southern China. The strength curves of vegetated coal-bearing soil under four factors were obtained. The Taguchi method was used to quantitatively analyse the effects of four factors. The microstructure of coal-bearing soil under D-W cycles and the theory of soil reinforcement by VR were discussed. The results indicated that D-W cycles had a significant effect on the cohesion and internal friction angle ( ). The internal friction angle was little affected by the water content and VR content, which had considerable influence on the cohesion. The cohesion could be improved with less than 2% VR content. The cohesion was the largest for no D-W cycles, 10% water content, and 2% VR content. The links between mineral particles go from a stable layered structure to unsteadiness chain structure with the increase in the number of D-W cycles.

A complex interface exists between water flow and solid particles during hydraulic soil erosion. In this study, the particle discrete element method (DEM) has been used to simulate the hydraulic erosion of a granular soil under moving bed conditions and surrounding terrain changes. Moreover, the weakly compressible smoothed particle hydrodynamics (WCSPH) approach has been exploited to simulate the instability process of the free surface fluid and its propagation characteristics at the solid–liquid interface. The influence of a suspended medium on the water flow dynamics has been characterized using the mixed viscosity concept accounting for the solid–liquid mixed particle volume ratio. Numerical simulations of wall-jet scouring and reservoir sediment flushing on a mobile bed were performed and validated with experiments. The results show that the proposed WCSPH– DEM coupling model is highly suitable for determining parameters, such as the local maximum scour depth, the scour pit width, and the sand bed profile. The effects on the hydraulic erosion process of two important parameters of the mixed viscosity coefficient (initial solid volume concentration and initial viscosity coefficient) are also discussed to a certain extent in this study.

The Interface Agent for Old Wall Tiles (IAWT) is an environmentally friendly material. However, its application in engineering is limited by its tendency to lose adhesion under harsh conditions. Factors such as freeze-thaw cycles, wind vibrations, rainfall, and thermal stress negatively affect the bond strength of IAWT. This study investigated the effects of PTB emulsion on various properties of IAWT, including bond strength, freeze-thaw resistance, wind vibration resistance, compressive-flexural ratio, water absorption, and microstructure. Orthogonal experiments were conducted to examine the impact of three key factors on the macroscopic properties of IAWT. The results indicated that increasing the ratio of PTB emulsion to water (P/W) improved bond strength under normal environmental conditions and enhanced freeze-thaw and wind vibration resistance. Furthermore, a higher P/W ratio reduced both the compressive-flexural ratio and water absorption. The addition of PTB emulsion slowed the hydration reaction, increased the number of micropores, and reduced the cumulative pore volume. Furthermore, it enhances the bond strength between the coating and the base layer, thereby increasing the durability of the renovation project for old walls. These enhancements yield positive economic and environmental benefits.