The frequency of mudflow disasters induced by rainfall in the Loess Plateau is increasing with the occurrence of global warming. The initial water content is one of the basic properties of soil, which affects the initiation of loess mudflow. In this work, the field study of the debris flow gullies in Yan’an City, Shaanxi Province, China, was conducted, and the main factors that induce gully loess mudflow were summarized. Based on the investigation results, a flume model was designed to carry out flume tests with different initial soil water contents. The experimental results demonstrate the following. (1) Different initial soil water contents lead to different soil failure models. The damage of soil by water flow when the soil water content is in the range of 0−5% is mainly gully erosion; that within the range of 10−15% is mainly rill surface erosion; that within the range of 20−25% is mainly dam breach failure. (2) When the water content of loess is equal to or less than 5% or equal to or greater than 20%, soil can promote the formation of loess mudflow, and the destruction of soil is more likely to cause mudflow disasters. In contrast, when the water content is within 10−15%, loess mudflow is not easily produced. The research results of the initial water content provide not only theoretical support for the study of loess mudflow disasters, but also a reference for the prevention and control of loess mudflow disasters in the Loess Plateau.

The intricate morphology of porous media can considerably affect the progression of penetration and the diffusion of grouting slurry. In this study, a Newtonian fluid’s refined seepage motion equation was proposed to incorporate the impact of tortuosity on the grouting process into gravel soil, and the column-hemispherical penetration grouting mechanism was analyzed using the method of theoretical analysis. Utilizing secondary-development programming techniques, a numerical simulation program was developed with COMSOL Multiphysics to model the penetration grouting mechanism of a Newtonian fluid in a column-hemispherical pattern, considering a medium’s tortuosity. The penetration grouting process of Newtonian cement into gravel soils was then simulated. Finally, the theoretical analysis, experimental values, and numerically simulated values were compared.The findings suggested that incorporating the tortuosity of porous media is more efficacious in depicting the penetration and diffusion behavior for Newtonian fluid grouting in porous media, as compared to omitting the tortuosity. The findings of this study contribute to a better understanding of grouting engineering in porous media strata, guiding practical design and construction.

Debris flow, the most extensive and most severe geological hazard along the Karakoram Highway, frequently blocks the Karakoram Highway. Based on the methods of field measurement, indoor statistical analysis and theoretical research, this paper discusses the relationship between the four types of debris flow along the Karakoram Highway. The four types are the rain type, the rain glacier type, the glacier ice lake break type and the freeze–thaw type, and their particle characteristics and gully slope are also considered in the discussion. The results are as follows: (1) The provenance particle size of debris flow is controlled by the type of debris flow. Generally, the provenance average particle equivalent diameter of the debris flow induced by the glacier ice lake type is relatively small, followed by the freeze–thaw type and glacier ice lake break type, and the equivalent diameter of the debris flow induced by the rain type is relatively large; (2) The gully slope coefficient of the debris flow $C$ along the Karakoram Highway is greater than 1, and it increases with the increase in gully slope $\alpha$, that is, the larger $C$ is, the steeper the gully slope will be; (3) The gully slope coefficient $C$ and the average particle equivalent diameter $D$ of the four types of debris flow are distributed in the ellipse with them as the axis. This ellipse quantitatively describes the relationship between the gully slope of the four types of debris flow and the corresponding provenance particle characteristics. This paper analyzes the formation and causes of debris flow along the Karakoram Highway. It accurately understands the scientific connotation of debris flow formation in the surface matrix layer and improves the diversity, stability, and sustainability of the ecosystem. The paper also proposes ideas and suggestions for promoting the ecological protection and restoration of the Karakoram Highway. Therefore, the research has a certain theoretical significance and practical application value for the appropriate selection and rational design of the debris flow prevention projects along the China–Pakistan Highway.

The diffusion progress of grout is hindered by groundwater, which means the diffusion distance cannot reach the designed values required in engineering for water plugging or reinforcement. In this study, based on the generalized Darcy’s law and the continuity equation of steady column penetration, a column diffusion mechanism for Bingham fluid, considering the displacement effect of grout on groundwater, is proposed. This diffusion mechanism is then validated by the penetration grouting experiments that have been previously performed. The influences of the grouting pressure, groundwater pressure, water–cement ratio and penetration coefficient of porous media on the diffusion radius are analyzed. Based on the Comsol Multiphysics platform, a three-dimensional numerical simulation program for this mechanism is developed using computer programming technology. Numerical simulations of the penetration and diffusion morphology of Bingham cement grout in porous media are then carried out. The results show that the theoretical calculation values of diffusion radius obtained from this mechanism are closer to the experimental values than those obtained from the column penetration grouting theory of Bingham fluid, without considering the displacement effect. The results of this study can provide theoretical support for practical grouting engineering.

Taking the Niumian Gully landslide–debris-flow geohazard chain as an example, we analyze the disaster mechanism of the landslide–debris-flow geohazard chain and its evolution process through field investigation as a reference for disaster prevention and risk reduction in areas with strong earthquakes by analyzing the accumulative sliding amount and the critical rainfall for debris flow formed by loose deposits. Due to the 8.0 Ms earthquake in Wenchuan, the cumulative sliding of the slope reached 230.51 m, much greater than the critical sliding in the Longmen Mountain earthquake area. Permanent damage to the slope occurred, resulting in a landslide, which provided the material source for the occurrence of debris flows. When the study area experienced concentrated rainfall (e.g., exceeding 10.31 mm/h or 54.67 mm/d), loose deposits in the basin began to form a debris flow, causing a landslide–debris-flow geohazard chain. During the evolution process of the geohazard chain, the following stages were observed: pre-earthquake gestation, landslide starting during a strong earthquake, landslide blocking a channel and forming a dammed lake, bursting of the dammed lake flood–debris-flow, sliding of loose deposits, and reciprocating loose-deposit sliding and debris flows. Thus, the formation of the Niumian Valley geohazard chain can be attributed to the combined result of strong earthquake activities and rainfall. In addition, under the action of rainfall, the occurrence of the debris flow and unstable sliding of loose deposits also caused the reciprocating occurrence of debris flows, loose-deposit sliding, and flood-induced debris flows in the study area.

The sedimentation basin is an important part of hydraulic engineering. Because the prototype size is too large and not easy to analyze, Mike 21 has the advantages of easy input, conversion, analysis, and demonstration of data results, which are flexible and convenient; however, this method has not been used in hydraulic engineering by previous researchers. This research used the sedimentation basin of the Yellow River Diversion Project as the research object, and a simulation model of the sedimentation basin channel #1 was developed using Mike 21 software to analyze its water and sediment characteristics and conditions in different periods. Using numerical simulation methods, three types of sedimentation basin operation schemes were targeted, the sedimentation changes and sedimentation law of channel #1 were evaluated in each scheme, and the sedimentation effects were compared. The results show that in conditions of different incoming water and sediment and diversion timings during the flood and non-flood seasons, the sedimentation basin adopts an operation scheme to lower the outlet water level, and the siltation volumes are 180,000 and 150,000 m³ lower than the high-outlet water levels, respectively. Moreover, its siltation status is significantly improved, which can effectively extend the service life of the sedimentation basin, prolong the period of silting removal by about 3.5 months, and provide a scientific basis and reference for the optimization of the operation mode of the sedimentation basin in other types of hydraulic engineering.