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.

This study presents experimental results from scale model tests on laterally loaded bridge pile foundations in soils subjected to seasonal freezing. A refined finite-element model (FEM) was established and calibrated based on data obtained from the experiments. Furthermore, the model was utilized to investigate the impact of soil scouring depth on the lateral behavior of bridge pile foundations embedded in seasonally frozen soils. The findings indicate that soil freezing significantly enhances the lateral bearing capacity of the pile-soil interaction (PSI) system while reducing lateral deflection of the pile foundation. However, soil freezing results in increased damage to the pile foundation and upward movement of the plastic zone toward the ground surface. Under unfrozen conditions, significant plastic deformations occur on the ground surface and even inside the piles due to the extrusion effect. Additionally, increasing soil scouring depth significantly reduces the lateral bearing capacity of the PSI system while also increasing lateral deflection of the pile foundation for a given load level. Notably, when the scouring depth exceeds 2 m in unfrozen soils, the entire pile experiences obvious deformation and inclination, exhibiting a short-pile behavior that negatively affects the lateral stability of the pile under lateral loads.

To address scour hazards surrounding offshore foundations, a new method employing novel alkali-activated cementitious grout (AACG) has been proposed for improvement of seabed soil. Ground granulated blastfurnace slag (GGBFS) was replaced by fly ash (FA), steel slag (SS) or FA + SS to prepare precursors, the replacement amounts were 10 %, 20 %, 30 % and 40 %. Fresh-state and mechanical properties, minerals and microstructures were investigated. A novel scour simulation test device was developed to simulate engineering conditions of scour and remediation. Flow-soil coupled scour resistance tests were conducted, shear tests and SEM measurements of solidified soil were carried out. The results showed that the optimal ratio of GGBFS:FA:SS was 6:2:2 for AACG. The optimized AACG has better fluidity and lower brittleness, and its 28 d unconfined compressive strength (UCS) achieves 13.5 MPa. For AACG solidified soil, the maximum scour depth was reduced by 33.3 % and the maximum sediment transport amount was decreased by 53.2 %, which were compared to those of cement - sodium silicate (C-S) double slurry. Moreover, the increase degrees of internal friction angle, cohesion and critical shear stress were 700 %, 7.9 % and 786 %, respectively. The scour resistance of AACG solidified soil was superior. The inherent relationship between UCS and critical shear stress was discussed. UCS can be used to rapidly assess the scour resistance of consolidated soil. This study introduced an eco-friendly AACG as an innovative stabilizer for soil reinforcement around offshore structural foundations, offering significant application and environmental values for scour control.

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.

The response of the bridge to the assessment of flood damage is constrained by a restricted examination of soilspecific vulnerabilities and the hydrodynamic forces linked to local scour. The research study will, consequently, aim to address these knowledge gaps in assessing the structural susceptibility of bridges to flooding in very stiff clay (type B) and medium dense sand (type C) soil. This research aims to analyse the behaviour and response of the bridge model when subjected to varying depths of local scour across different soil types. To accomplish this objective, a three-dimensional numerical model is employed for a standard three-span reinforced concrete bridge. In the conducted experiment, a total of 192 scenarios were simulated, considering four distinct levels of local scour depth across two different soil types. The analytical results indicated a notable increase in pier displacement because of the augmented scour depth. The recorded displacement in medium dense sand exhibited a 42 percent increase because of the rise in scour depth. Consequently, it was determined that the impact of erosion caused by flooding on bridges spanning rivers must be accounted for when designing the bridges' 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.

This study explores the transverse response of bridge piers in riverbeds under a multi-hazard scenario, involving seismic actions and scoured foundations. The combined impact of scour on foundations' stability and on the dynamic stiffness of soil-foundation systems makes bridges more susceptible to earthquake damage. While previous research has extensively investigated this issue for bridges founded on piles, this work addresses the less explored but critical scenario of bridges on shallow foundations, typical of existing bridges. A comprehensive soil-foundation structure model is developed to be representative of the transverse response of multi-span and continuous girder bridges, and the effects of different scour scenarios and foundation embedment on the dynamic stiffness of the soil-foundation sub-systems are investigated through refined finite element models. Then, a parametric investigation is conducted to assess the effects of scour on the dynamic properties of the systems and, for some representative bridge prototypes, the seismic response at scoured and non-scoured conditions are compared considering real earthquakes. The research results demonstrate the significance of scour effects on the dynamic properties of the soil-foundation structure system and on the displacement demand of the bridge decks.

High-rise pile cap structures, such as sea-crossing bridges, suffer from long-term degradation due to continuous corrosion and scour, which seriously endangers structural safety. However, there is a lack of research on this topic. This study focused on the long-term performance and dynamic response of bridge pile foundations, considering scour and corrosion effects. A refined modeling method for bridge pile foundations, considering scour-induced damage and corrosion-induced degradation, was developed by adjusting nonlinear soil springs and material properties. Furthermore, hydrodynamic characteristics and long-term performance, including hydrodynamic phenomena, wave force, energy, displacement, stress, and acceleration responses, were investigated through fluid-structure coupling analysis and pile-soil interactions. The results show that the horizontal wave forces acting on the high-rise pile cap are greater than the vertical wave forces, with the most severe wave-induced damage occurring in the wave splash zone. Steel and concrete degradation in the wave splash zone typically occurs sooner than in the atmospheric zone. The total energy of the structure at each moment under load is equal to the sum of internal energy and kinetic energy. Increased corrosion time and scour depth result in increased displacement and stress at the pile cap connection. The long-term dynamic response is mainly influenced by the second-order frequency (62 Hz).

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.

Bridge piers embedded in a riverain region are commonly supported by pile foundations. This provides a flexible restraint to the bridge pier instead of a theoretical rigid foundation type. In this work, a cylindrical bridge pier with a monopile foundation is introduced as an example. A modeling framework is proposed to investigate the dynamic response of bridge piers to the impact of flash flooding. The fluid-structure interaction is directly investigated via a two-way fluid-structure coupling approach and the p-y springs distributed over the interface between the soil and pile are adopted to model the lateral restraints from the soil. The effect of the soil-structure interaction (SSI) on the structural dynamic response is investigated on the basis of 3D numerical models with and without a pile foundation. Moreover, the soil around the pile foundation is vulnerable to erosion by flood flow. This continuous exposure of the pile foundation reduces the lateral load bearing capacity and consequently increases the dynamic responses of bridge structures to flash flooding. To demonstrate the effects of increased exposure of bridge pile foundations on structural dynamic responses, several different scour depths with scour ratios ranging from 0 to 0.5 are included in the numerical analysis. Two different considerations of the pile bottom are included in this study: completely fixed and only vertically fixed. The behavior of bridge piers subjected to flash flooding is thoroughly analyzed, and the damage mechanisms for these two foundation types are investigated. The relationships between peak responses and fundamental periods are determined via regression analysis.