This study investigated how soil properties affect levee erosion and foundation scouring by evaluating the behavior of loose and cohesive (mixed) soils beneath a rigid crest under overflow conditions and analyzing flow dynamics within the scoured hole to understand the scouring mechanism. Four cases were examined with varying overtopping depths (Od): LS-FS, LS-FM, and LM-FS, at Od = 2 cm, and LS-FM at Od = 3 cm, where 'L' stands for levee, 'F' for foundation, 'S' for sand (#8), and 'M' for mixed soil (20% silt + 80% sand #8). The results revealed distinct differences among the cases. Notably, erosion of the back slope in the LM-FS case was delayed fourfold compared to LS-FS. In the LS-FM case, breaching of the levee body was delayed by 1.6 times compared to the LS-FS case with a 2 cm overtopping depth. Moreover, different scour hole geometries with complex flow patterns occurred in different timespans. Particle image velocimetry (PIV) was utilized on two physical scoured hole models to analyze the flow behavior within these scoured holes. The PIV analysis revealed the formation of twin eddies, moving in opposite directions and shaped by the nappe flow jet, which was instrumental in the development of the scour holes. This study found that foundation cohesion is more essential than the levee body in delaying levee breaches under rigid crest. Additionally, it revealed the role of twin eddies, especially the levee-side eddy, in increasing the size of the scoured hole upstream and causing levee breaches.

Wall piers are widely used to enhance lateral stability in bridges with tall piers and relatively narrow decks. For this type of structure, the longitudinal direction of the bridge is commonly acknowledged as the governing direction for seismic performance, with wall piers serving as the seismic critical members. However, progressive scouring reduces foundation strength and stiffness, leading to increased transverse seismic deformation. This deformation amplifies the risk of pile damage and may shift the seismic critical member to the foundation. This study investigates the seismic performance of wall pier bents in bridges, explicitly focusing on the effects of riverbed scouring. Through a Taiwan-based case study, seismic performance is evaluated at various scour depths, identifying the seismic critical member through capacity spectrum analysis and the peak ground acceleration corresponding to the performance limit of the wall pier bent. The findings highlight that seismic performance is frequently controlled by the transverse direction, emphasizing the foundation as the seismic critical member. The effect of employing foundation strengthening as a retrofit strategy is also assessed, revealing that it provides only limited improvement in seismic performance. Even after retrofit, the seismic performance of wall pier bents remains primarily governed by the pile foundation.

Due to the insufficient burial depth of shallow-buried foundation bridges, foundation voiding easily occurs during floods or rapid water flows. When heavy vehicles pass over these partially voided bridges, the stress state of the foundation deteriorates instantaneously, causing critical components to exceed their load-bearing capacity in a short period, leading to a chain reaction that results in the rapid collapse and overall failure of the bridge structure. Previous numerical simulations of bridge water damage often neglected the strong coupling between water flow, soil, and structure during the scouring process. This paper applies a fluid-solid coupling simulation modeling method for bridge damage behavior under scouring action to study the structural damage behavior of shallow-buried foundation bridges under the combined effects of flood scouring and heavy vehicle load. This method employs point cloud reverse engineering technology to solve the difficult problem of converting the complex scour morphology around the foundation under flood scouring into a structural model, and investigates the multi-hazard damage behavior of shallow-buried foundations by coupling extreme hydraulic effects on the pier surface and placing the most unfavorable heavy vehicle loads on the bridge deck.

The increasing frequency of geotechnical disasters and climate-related land degradation underscores the need of resilient soil erosion mitigation. This study investigates the effectiveness of Cr3+-crosslinked xanthan gum (CrXG), a cation-crosslinked gelation biopolymer with time-dependent gelation and water-resistant properties, in mitigating hydraulic soil erosion. Through the erosion function apparatus test, rheological analysis, and microscopic observations, results indicate notable improvements in soil erosion resistance with CrXG treatment, elucidating distinct reinforcing mechanisms attributable to the gel state of the biopolymer hydrogel. The addition of 0.25% CrXG to the soil mass significantly improves critical shear stress and critical velocity, reducing the erodibility coefficient by four order magnitudes compared to untreated sand. Within 48 h, the transition from a viscous to rigid gel state in CrXG, driven by cation crosslinking, transforms the soil from high (II) to low (IV) erodibility class. Scour predictions using the program, based on river hydrograph conditions, indicate a substantial delay in reaching a 1-m scour depth. This study highlights CrXG-soil composite's potential as an advanced geomaterial for mitigating geohazards such as floods and stream scouring, while offering insights into its competitiveness with conventional soil stabilization techniques.

Oil pipelines are susceptible to significant hydraulic erosion from mountain torrents during the flood season when passing through the mountain valley area, which can lead to soil erosion on the pipe surface and expose the pipeline. Accordingly, this study centers on investigating the critical issue of the failure mechanism caused by flash flood erosion in the exposed of oil pipelines. Both indoor testing and numerical simulation research methods are employed to analyze the flow field distribution characteristics of flash floods in proximity to an exposed pipeline. This study explores the patterns of soil loss around pipelines of varying pipe diameters, levels of exposure, and pipe flow angles. In addition, the spatial and temporal evolution mechanism of pipelines overhang development under the action of flash floods was elucidated. The experimental observations indicate that as the pipe diameter increases, the failure rate of the soil surrounding the pipe accelerates, while the erosion effect on the soil around the executives becomes more pronounced. Additionally, a larger pipe flow angle leads to a reduced soil loss in the downstream direction of the pipe. During flash flood events, the scouring action on the soil surrounding the pipe leads to rapid compression of the flow field around the pipe, while the vortex at the pipe's bottom exacerbates soil corrosion. Additionally, the maximum pressure exerted on pipeline surfaces at pipeline flow angles of 30 degrees, 60 degrees, and 90 degrees is 14,382 Pa, 16,146 Pa, and 17,974 Pa, respectively. The research results offer valuable insights into pipeline, soil, and water conservation projects in mountain valley regions.

Scouring of roadbeds along river highways poses a significant threat to the safety of mountain roads. Relying on the Karakorum Highway (KKH) water damage disaster remediation project, using the erosion function apparatus and theoretical analysis, we studied the scour rate, starting shear stress, and the variation of theoretical model parameters in clay-coarse sand mixed soil samples with different clay contents. We also explored the scour characteristics and damage modes of mixed soils based on the soil skeleton theory. The following conclusions were drawn. As the clay content increases, the starting shear stress of the soil sample rises, scour resistance is strengthened, and the scour characteristics transition from non-cohesive to cohesive soil scour characteristics. The distribution of cohesive fine particles varies from filling the voids between coarse particles to bonding with them, and ultimately separating the coarse particles. The damage mode of the mixed soil samples under scouring water flow varies depending on the filling pattern of coarse particles and clays. The Wilson model exhibits a good fit with the experimental data and can be applied to predict large shear stresses, compensating for the limitations of the over-shear stress model.