Experimental Study on the Accumulation Characteristics and Submergence Degree of Three-Dimensional Granular Rock Landslides in Shallow-Water Areas
Compared with landslides in deep-water areas, landslide masses sliding into shallow water can instantly cause significant changes in the local terrain in the near field, causing river blockages and even forming landslide dams, inducing strong disturbances to the surrounding water bodies. The resulting swells exhibit strong nonlinearity. It is necessary to analyze the water motion characteristics of loose rock landslides from a shallow water perspective and the inundation situation after water entry stops to study the near-field wave characteristics of landslide surges in shallow-water areas. Based on previous research on landslides and waves under static water conditions, this study considered the influence of hydrodynamic factors and combined the development characteristics of rock fractures in the Three Gorges Reservoir area to establish a three-dimensional model of scattered rock landslide surges. By analyzing the image sequence extracted using high-speed cameras, the evolution law of rock landslides during the sliding process is obtained based on the morphology and inundation situation of the accumulation body after a landslide body stops moving. Through experimental data and theoretical analysis, a method for determining the landslide inundation rate and the width of the accumulation body was developed. The research results can provide a theoretical basis and technical support for ensuring the safety of water conservancy and water transport projects in mountainous areas and preventing landslide hazards.
2. Simulation Methods of the Model Test
3. Results and Discussion
3.1. Division of the Landslide Movement Process
The movement of landslide masses is the most critical factor in generating swells, and its movement characteristics determine the final characteristics and degree of harm of the swells. Due to unfavorable topographical and geological conditions, mountains may be affected by a series of external environmental factors, such as rainfall, river erosion, reservoir water level fluctuations, and geological vibration, resulting in collapses and landslides. From mechanics and strain perspectives, the sliding mechanisms and motion characteristics of landslide masses under different types and environments are extremely complex and difficult to study; they remain the focus of contemporary research.
Current research methods on the movement characteristics of large and medium-sized rock landslides mainly include field surveys and measurements, physical model testing, theoretical analysis, and numerical simulation calculations. Due to the strong suddenness, short movement time, and a high degree of hazards of large and medium-sized landslides, existing research techniques still experience difficulty monitoring natural landslide movement processes. The landslide movement process can only be judged, speculated, and inverted based on on-site investigations of the geometric form and material composition of landslide deposits, residual traces, and other information after the landslide has occurred. Therefore, physical model tests have high practical value and important research significance for simulating the rock landslide movement process.
Starting stage of the landslide mass
Accelerated sliding stage of the landslide mass
Slow acceleration or deceleration stage of the landslide mass
Rapid deceleration stage of landslide mass
3.2. Experimental Simulation of the Movement Process of Loose Rock Landslides
In response to the four stages of landslide movement detailed above, model tests of a loose rock landslide were conducted and simulated with similarity to the landslide movement process in this study. The experiment used high-definition cameras to record the landslide movement process fully. It used a total video converter to convert the video collected during this process into images in order to clearly observe the changes in the shape of the landslide during the movement process.
Due to the small height difference between the simulated loose rock landslide and the water surface, the completion time of the above four processes was very short: approximately 1–3 s. This is in line with the strong suddenness and short movement time characteristics of actual large and medium-sized rock landslides. In fact, the movement patterns of the four stages of loose landslide particles are similar to the characteristics of layer moving, contact moving, and jump moving in river sediment movement. The movement of landslide particles after entering water is similar to the sedimentation, diffusion, and movement of sediment particles along slopes and riverbeds. At the same time, the movement of loose landslide particles is similar to the movement of debris flow and can thus be regarded as a type of debris flow or particle flow movement. Therefore, research can be conducted based on relevant theories in sediment motion mechanics.
3.3. Shape and Submergence Rate of Landslide Deposits
3.4. Identification of the Degree of River Blockage Caused by Scattered Landslides
In Equation (2), represents the blockage discrimination coefficient, also known as the blockage degree coefficient; represents the maximum bottom width of the underwater accumulation body (m); and represents the bottom width of the river channel (m).
The greater the value of , the greater the possibility of blocking the river and the more severe the potential blockage. If , it indicates the formation of landslide dams that block rivers, causing the most severe disasters.
Based on the structural characteristics of rock mass in the Three Gorges Reservoir area, the characteristics of main and tributary river channels, and the flow conditions, a three-dimensional granular rock landslide surge model test underwater flow dynamics was designed and conducted in this paper. The experimental simulation of the four stages: starting, accelerating, slowly accelerating or decelerating, and rapidly decelerating of the movement process of the landslide body was conducted, and the variation process of the movement speed with time was given. The morphological changes of the landslide during its movement were analyzed, and it was concluded that the submerged accumulation body partially presented the characteristics of an elliptical truncated cone. The submergence rate of the landslide body under various test conditions was calculated statistically, and the relationship between the dimensionless accumulation width, , and dimensionless landslide submerged accumulation volume, , was obtained using dimensionless fitting analysis. The results showed that the volume of the landslide body entering the water was directly proportional to the degree of river channel blocking. The research results in this article are only applicable to landslides in shallow waters; there may be deviations in deep waters. This experiment mainly studied the movement and accumulation characteristics of granular rock landslides; further research is needed on the movement and accumulation characteristics of steep rock and soil landslides.
Disasters Expo USA, is proud to be supported by Inergency for their next upcoming edition on March 6th & 7th 2024!
The leading event mitigating the world’s most costly disasters is returning to the Miami Beach
And in case you missed it, here is our ultimate road trip playlist is the perfect mix of podcasts, and hidden gems that will keep you energized for the entire journey-