Local Scour Hole Research Articles

Comparison of hybrid deep learning models for estimation of the time-dependent scour depth downstream of river training structures

Submerged weirs, mainly positioned downstream of bridges, play a key role in safeguarding against floods and long-term scour damage. However, the structural stability of these structures could be threatened by local scour holes. This study evaluates five deep learning algorithms—Deep Neural Networks, Convolutional Neural Networks (CNNs), Convolutional Extreme Gradient Boosting (CXGB), convolutional extremely randomized trees regression, and Self-Attention-based Convolutional Neural Network (SA-CNN) in predicting the evolution of scour depth. Using Hyperband and Bayesian optimization, the models were fine-tuned for maximum accuracy. Additionally, this study investigates the impact of two data splitting methods, including random pointwise sampling and case-wise sampling on model performance. Results indicate that the hybrid CXGB and the SA-CNN models outperform other models in terms of accuracy of the estimation of the time-dependent scour depth with R2 = 0.997 in pointwise and R2 = 0.878 in case-wise split strategies, respectively. This not only demonstrates the effectiveness of these sophisticated algorithms in time-dependent scour estimation but also clarifies the effects of various data sampling techniques on model performance. Finally, the contribution of features in provided estimations is discussed utilizing SHapley Additive exPlanations values. Results indicated that the time (T) and the ratio of the flow velocity to critical velocity U0/Uc had the greatest effect on the model outputs, while side slopes indicated a negligible effect on model output compatible with the physics of the problem.

Macro-element modelling for lateral response of monopiles with local scour hole via hyperbolic hardening relation

Monopile is a popular choice in the foundation supporting offshore wind turbines (OWTs), with local scour significantly impacting their lateral responses. Macro-element model, which encapsulates the response between the monopile and the surrounding seabed soils into a force-displacement relation, has been extensively developed to describe offshore foundations. However, such kind of models specifically targeting monopiles subjected to lateral loading in local scour remain underdeveloped. This work proposes a macro-element model with a succinct hyperbolic hardening relation for laterally loaded monopiles in local scour conditions, using the evolutionary polynomial regression (EPR) machine learning technique for easy and optimal design. First, the finite element model is verified and extended to generate force-displacement responses considering the monopile geometries, soil characteristics, and local scour geometries. These results are then utilised to determine the optimal hyperbolic hardening relation of the macro-element model. Next, the EPR technique is employed to determine the relationship between the hyperbolic hardening relation parameters and the influencing factors. Finally, the macro-element model is successfully evaluated by comparing with measurements from centrifuge tests and numerical solutions by finite element analysis, demonstrating its applicability in practical design and the ability to reproduce FEA results with a significant reduction in computational cost.

Numerical Analysis of Flow Structure Evolution during Scour Hole Development: A Case Study of a Pile-Supported Pier with Partially Buried Pile Cap

This study numerically investigates a pile-supported pier, which comprises a column with a partially buried pile cap and a group of piles, recognizing that partially buried pile caps lead to the highest scour depth. Most research has focused on equilibrium scour conditions in laboratory settings, overlooking the detailed dynamics of horseshoe vortices around pile groups. This study aims to clarify the flow structure and vortex dynamics at a pile-supported pier during local scour hole development stages using an in-house developed numerical model. The model’s accuracy is validated against flat-channel and compound pier reference cases. For the pile-supported pier, fixed bed geometry was used in flow simulations at selected scouring stages. Results show significant changes in flow structure and vortex formation with scour hole time development, particularly as the bed surface moves away from the pile cap. The study reveals variations in vortex size, number, and positioning, alongside turbulent kinetic energy and Reynolds shear stress distributions over time. High positive Reynolds shear stress near the bed during intermediate scouring stages highlights the complex interactions within the flow field. This research provides the first detailed visualization of flow structure evolution within a scour hole at a pile-supported pier.

Influence of local scour on the evolution of the failure envelope for suction caisson foundation

Local scouring significantly undermines the load-bearing capacity of suction caisson foundations and poses a daunting challenge to the integrity of offshore structures. This study numerically addresses the impact that the size and shape of the local scour hole have on both the monotonic bearing capacities and failure envelopes of suction caisson embedded in sandy soil. Different loading conditions - individually and combined - by integrating local scour parameters such as scour depth (Sd), scour width (Sw) and scour angle (φ) while maintaining realistic scour proportions are carefully evaluated. The obtained results show that (1) scour depth has a stronger influence on the ultimate bearing capacity than the influences of scour width and angle; (2) the horizontal bearing capacity shows increased sensitivity to variations in scour depth; and (3) both the horizontal bearing capacity and the moment bearing capacity reach a plateau and a steady state manifest itself when the relative scour depth exceeds a threshold value of 0.9. An empirical formulation to characterize the failure envelope within the horizontal force-moment (H-M) plane is finally proposed, which properly considers the effect of scour depth. These findings provide a valuable reference for ensuring structural resilience to local scour phenomena.

The dynamical response of turbulent flow to bed deformation under submerged discharge and plane vertical impinging jets

Abstract On the conditions of discharge under sluice gate and vertical jets, the research on the dynamical response of hydraulic elements to bed deformation is much concerned in the field of high-speed flow and hydraulic dredging but not be solved yet. Research achievement from numerical simulation are drawn as follows: (1) Under sluice gate discharge condition, the response of hydraulic elements to bed deformation is that the bed is deforming in the direction of the mechanical energy loss, the rate of the bed deformation and the mechanical energy loss near the local scour hole and the horizontal distance from the reattachment point to the maximum scour depth are all continuously varying with the scouring of time and synchronously approaching to its own certain value. (2) Under vertical jets discharge condition, the response of hydraulic elements to bed deformation is that the rate of bed deformation and the pressure of the maximum scour depth is monotonous continuously decreasing with the scouring of time and synchronously approaching to its own certain value.

Spatio-temporal characterisation of local scour around a circular bridge pier in cohesive soil with different clay/silt ratio

This paper presents new data on scour around a vertical pier in cohesive soils. It specifically focuses on the temporal evolution of local scour hole around the pier with increasing the clay/silt ratio content. Series of flume tests were performed using soil mixtures made with 85% fine sand and 15% fines. The fines fraction used in the soil mixtures includes silt, kaolinite clay, and various combinations of both with different proportions. The water velocity during the tests was kept constant and slightly above the erosion critical velocity of the fine sand used in the mixtures. A 3D laser scanner was employed to continuously record the geometry of the scour hole. Results show that increasing the Kaolinite clay in the fine fraction reduces significantly the scour. The mixture with a range around 7.5–10% of kaolinite clay fines content provides the threshold composition for cohesive soil behaviour effect in scouring process, recognized through scour pattern change. As the clay content increases, notable reductions are observed in the dimensions of the scour hole. Furthermore, the temporal evolution of maximum scour depth measured in flume was in agreement with the results from SRICOS-EFA (Scour Rate in COhesive Soil - Erosion Function Apparatus) method.

An Investigation into the Lateral Bearing Performance of a Single Pile Embedded at a Three-Dimensional Asymmetric Local Scour Site Using the Modified Strain Wedge Model

The scouring effect is widely acknowledged as a primary contributor to the weakening in the bearing performance of offshore piles; it often results in asymmetric scour patterns around the pile. To meticulously examine the impact of three-dimensional asymmetric local scour on the lateral bearing performance of a single pile, the Boussinesq solution is employed to determine the effective stress within the soil encompassing the pile, considering the presence of a three-dimensional asymmetric local scour hole. Utilizing the strain wedge model, the calculation method for the lateral bearing performance of a single pile under the condition of three-dimensional asymmetric local scour is established. The validity of this approach is established, and parameter analysis unveils the effect of varying sizes of three-dimensional asymmetric scour holes on the mechanical properties and displacement performance of a single pile. The analysis reveals that, as scouring dimensions around the pile escalate, the impact of scouring on single-pile lateral displacement and internal forces intensifies, leading to a decrease in the lateral bearing performance of a single pile. At a constant scour depth, the bottom area of the upstream scour hole significantly influences the displacement performance of a single pile. When the bottom length Swb1 of the upstream scour hole grows by 1 time, 4 times, and 8 times, the lateral displacement of a single pile at a buried depth of 6 m is augmented by approximately 0.41%, 1.65%, and 2.06%, respectively. The simplified model obtained via the modified strain wedge model and Boussinesq solution can provide a theoretical basis for the preliminary design of a single pile under asymmetric scour hole conditions.

Experimental Study on Influence of Different Patterns of an Emergent Vegetation Patch on the Flow Field and Scour/Deposition Processes in the Wake Region

AbstractFlume experiments were conducted to comprehend the impact of different patterns of an emergent vegetation patch on the flow field and the scour process in natural rivers. Velocity measurements, flow visualization, and scour tests were undertaken around different vegetation patch patterns, which were simulated inspired by the expansion process of a typical instream vegetation. The patch expansion process was idealized with an initially circular patch of rigid emergent stems becoming elongated due to positive and negative feedbacks. The expansion of the vegetation patch was considered to occur in three stages, in which the density of the patch from the previous stage was increased while the patch was also elongated by connecting at its downstream side with another sparser vegetation patch. These stages were replicated succesively by increasing the density and elongating the patch. In this way, two processes (i.e., elongation and decrease in permeability), which usually have hydrodynamically opposite effects on flow fields, were simulated at the same obstruction. Despite generally elongated obstacles being streamlined bodies, the morphometric analysis obtained by laser scanner revealed that streamlined elongation of permeable patches amplifies global scour and enhances localization of the local scour hole. This situation implies that as the patch expands, in the wake region, the steady‐wake region becomes shorter, turbulence diminishes, lateral shear stress enhances, and deposition cannot occur far from the patch. Consequently, as the patch expands, the hydrodynamic consequences may restrict further patch expansion after a certain length/density.

Refined Simulation Study on the Effect of Scour Environments on Local Scour of Tandem Bridge Piers

Ice cover is a natural phenomenon unique to rivers in cold regions, and its existence is one of the reasons for the collapse of structural foundations of bridge piers across rivers. In order to understand the influence of different scouring environments on the hydrodynamics and sand bed morphology in the local scour holes around bridge pier foundations, this paper simulates the dynamic evolution process of the local scouring of tandem combination piers under open-flow and ice-cover environments, based on a turbulence model using the Reynolds-averaged Navier Stokes (RANS) method and a sediment transport model considering the slope collapse effect, respectively. This study also takes the vortex flow and shear stress distribution at different characteristic moments of the pier perimeter section as the penetration point to analyze the effect of the influence law of the scouring environment on the morphology and relative time scale of the scour hole, and makes a detailed comparison with the results of the indoor flume test. The results of this study show that: for local scouring in open-flow conditions, sediment initiation is doubly inhibited and the hydrodynamic forces in the scouring hole are weakened; the local scouring caused by ice cover contributes to the total scouring of the submerged pier within its coverage area, which significantly increases the depth and range of the local scouring hole; and, although the interaction of turbulent eddies and shear stress on the pier side is the main dynamic mechanism of the scouring generated around the pier, the two have a strong correlation. The results of this study, obtained by accurately quantifying the amount of eddies and shear stress around the pier, are the basis for the reasonable estimation of the maximum local scouring depth, which can provide a reference for the study of the evolution of the riverbed around submerged structures in cold areas and is essential to avoid structural damage to the piers and reduce the economic loss of traffic..

Geometry of Local Scour Holes at Boulder-like Obstacles during Unsteady Flow Conditions and Varying Submergence

Local scour holes are erosional bed structures that are related to different scientific disciplines in Earth science and hydraulic engineering. Local scouring at naturally placed boulders is ubiquitous, but many competing factors make it difficult to isolate the effects of a given variable. This is especially true for local scouring at natural instream obstacles that are exposed to unsteady flow conditions in the course of flood hydrograph experiments. Experimental investigations in laboratory flumes offer the advantage that boundary conditions can be systematically varied. We present novel experimental data on the impact of the submergence ratio, hydrograph skewness, and flow intensity on local scouring at boulder-like obstacles during unsteady flow and evaluate the effect of discharge chronologies. In total, 48 flume experiments on subcritical clear-water conditions and channel degradation were performed. The experimental results reveal that local scouring dominantly occurred at the rising limb when flow depth was comparable to the obstacle size, so the obstacle was unsubmerged. The steeper the rising limb, the quicker the local scour hole matured. The experimental results are relevant for the hydraulic interpretation of local scour holes found at boulders in the field. They may be utilized as a proxy for the minimum duration of the beginning stage of a flood.

Numerical investigation on horizontal deformation of large diameter monopile under cyclic wave loading with local scour holes

Seabed liquefaction and local scour around the offshore wind turbine (OWT) monopile have significant effects on the horizontal bearing capacity of the foundation. The horizontal displacement of the monopile at the seabed mudline is one of important factors considered in the foundation design. In this study, the effects of local scour and soil liquefaction on the monopile horizontal displacement were investigated. The dynamic response of sandy seabed with various densities under wave loading was simulated by adopting the Cyclic Mobility (CM) model. The numerical model was compared with previous experimental results. Then, the effects of local scour and soil liquefaction on the monopile horizontal bearing capacity were discussed. The differences in the effects of local scour and liquefaction on the horizontal displacement of monopile in the case of sandy seabed with different densities were compared. Numerical results shown that the effect of soil liquefaction caused by the vertical cyclic wave loading on the monopile horizontal bearing capacity is more significant than that of local scouring and horizontal cyclic loading, especially in loose sandy seabed. For dense sandy seabed, the local scour of the seabed has a more significant impact on the horizontal bearing capacity of the foundation.

Local Scour of Highway Cross Drainage Structures

In this paper methods for determination of maximum local scour depth and eroded material volume downstream of highway drainage structures were developed. Severe local scour leads to undermining followed by collapsing of the drainage structure. The analysis method is based on integrating a new technique of improved drainage structure outlet geometry, jet hydraulic characteristics and soil properties. The jet velocity, induced shear stress, critical shear resistance to erosion and particle size are the main factors that control the erosion process downstream of a drainage structure. The study is of experimental and theoretical nature. The developed mathematical model was calibrated using collected field data in addition to laboratory tests. The produced scour holes were plotted for each laboratory run and the scour hole depth, width and length were measured. A semi- empirical relation has been developed for predicting the depth of local scour hole. It is based on Densimetric Froude number. It is found that the semicircular apron gives less scour depth and width when compared to the linear front apron. The comparison of the model outputs and field study is found of a good agreement. The model is recommended for engineering design of highway drainage structures located on streams of sandy bed.

A comparison between artificial neural network algorithms and empirical equations applied to submerged weir scour evolution prediction

Estimating the time evolution of a local scour hole downstream of submerged weirs can help determine the maximum scour depth and length and is essential to designing submerged weir foundations. In the current study, artificial neural networks with a backpropagation learning algorithm were used to estimate the temporal variation of scour profiles downstream of submerged weirs under clear water conditions. Physical factors, such as the flow condition, weir size, and sediment characteristics, are general scour considerations. Two sets of data combinations, namely original and non-dimensional data, were utilized in developing the backpropagation network (BPN) model. Using the data combinations and a trial-and-error method, the appropriate number of hidden neurons in the model architecture was determined. The results indicated that using non-dimensional variables as inputs in estimating the time evolution of scour holes downstream of a submerged weir is more suitable for the BPN model. Comparisons of the prediction results of the BPN model and an empirical regression formula revealed that the BPN model was more accurate and more direct in predicting the temporal variation of the local scour hole profile. In addition, sensitivity analysis showed that the dimensionless time exerted the most significant impact on the time evolution of the non-dimensional scour hole profile.

Dynamic pressure fields in a local scour hole formed by a submerged wall jet

Previous studies investigated the flow in a local scour hole mainly from two perspectives, i.e. mean velocity and turbulence, but there is no literature exploring it from the perspective of pressure. This study investigates the dynamic pressure fields in a local scour hole formed by a wall jet using PIV (particle image velocimetry) data to solve the Navier–Stokes (N-S) and Reynolds-averaged Navier–Stokes (RANS) equations, respectively. A comparison between the two cases with the effect of turbulence (solved by RANS equations) and without the effect (by N-S equations) reveals that turbulence reinforces pressure in the local sour hole. The wall jet experiences cyclical energy transitions in the forms between kinetic energy and pressure energy over its interactions with the sediment bed and the water surface. It is revealed that pressure energy is predominant by examining the ratios of the pressure energy to the average kinetic energy in the scour hole.

Temporal variations of sediment and morphological characteristics at a large confluence accounting for the effects of floodplain submergence

The large confluence between the Yangtze River and the outflow channel of Poyang Lake is receiving attention due to its importance in flood control and ecological protection in the Yangtze River basin. There is a large floodplain along the outflow channel of Poyang Lake, which is submerged during high flow and dry during low flow. The effects of the submergence of this floodplain on sediment and morphological characteristics at this large confluence have not been known. Hence, a field investigation was done in March 2019 (relatively high flow, Survey 3) to complement the previous field studies done in August (high flow, Survey 1) and December 2018 (low flow, Survey 2) to identify the temporal variations of sediment and morphological characteristics considering the submergence of this large floodplain. The predominant sediment transport modes were wash load for Poyang Lake and confluence particles and mixed bedload/suspended load for the Yangtze River particles. The sediment transport processes were largely affected by both the secondary flows and the water density contrast between the tributaries with a lock-exchange sediment rich, denser flow moving across the inclined mixing interface in Surveys 1 and 2. The sediment flux across the mixing interface was weakened in Survey 3 when the density contrast was very small. The stagnation zone near the confluence apex had a low sediment concentration and played a role in preventing the sediment flux exchange between the two flows, and its size, and, thus, its importance as a barrier to sediment mixing were related to the submergence of the floodplain. The bed morphology with the local scour holes at the confluence was largely affected by the large-size helical cells, and this kind of effect was weakened as the secondary flows got restricted in Survey 3. The current results expand the database and knowledge on the sediment transport and morphological features of large river confluences.

Modeling of Progressive Scouring of a Pier-on-Bank

Scour, caused by swiftly moving water, can remove alluvial sediment and soil, creating holes surrounding a bridge component and compromising the integrity of the bridge structure. Such problems can be equally critical for bridges with piers-on-bank bridges subjected to severe storm and flooding issues. In this paper, the Phillips Road Bridge over Toby Creek (35°18′28.2″ N 80°44′16.6″ W, Charlotte, NC, USA), a pier-on-bank bridge with critical/significant local scour holes and deep riverbank erosion cuts was selected as case study bridge. To investigate the scour effect on the bridge with pier-on-bank performance, the scoured area around a single pier is first quantified using a terrestrial laser and then modeled using nonlinear finite element (FE) analysis, where the local scour is modeled as progressive mass losses using the Element Removal (ER) technique. The FE results are compared to the design loading scenario and the results substantiated that the local scouring could cause large deflection and increased bending moment on the bridge pier.

Investigation of Local Scour Hole Dimensions around Circular Bridge Piers under Steady State Conditions

The local scour around bridge piers is one of the main causes of bridge failures. In this study, scour hole dimensions around circular bridge piers were investigated under clear water scour conditions for various steady flow rates. The experiments were performed with four different bridge pier diameters and seven different flow rates by using uniform sediment with a median diameter of 1.63 mm and geometric standard deviation of 1.3. After each experiments the bathymetry of scour hole was determined. New empirical equations to estimate scour hole length, scour hole width and scour hole volume (V) are proposed by using experimental findings and experimental data available in the literature. The experimental results were also compared with those calculated using several empirical equations given by previous studies. Since there is a lack of data about scour hole dimensions, the experimental findings presented in this study are useful for the researchers investigating the local scour process, and have contributed to the few experimental data in the literature.

Effects of local scour on failure envelopes of offshore monopiles and caissons

Local scour may induce bearing capacity loss of the foundation significantly by removing soil around the foundation and it has become one of the pivotal factors causing the failure of structures in offshore engineering. Therefore, it is indispensable to investigate the effect of local scour on bearing capacity behaviour of foundations. This paper focuses on the effects of dimensions of local scour hole on both ultimate bearing capacities and failure envelopes of the monopile and the caisson in undrained soil with different soil strength heterogeneity ratios using three-dimensional finite element method. The results show that the scour depth has a more significant effect on the ultimate bearing capacity than the scour hole angle. Meanwhile, the scour depth has a more significant effect on the lateral bearing capacity (i.e., horizontal bearing capacity and moment) than on the vertical bearing capacity. For given dimensions of local scour hole, the effect of local scour on the bearing capacity decreases as soil strength heterogeneity ratio increases. Moreover, local scour affects not only the size of the failure envelopes of the monopile and the caisson, but also their shape. Based on the above findings, a procedure of designing the monopile and the caisson to consider local scour effect is proposed, which could be helpful to the design of the foundations in practical engineering.

Using side flow jets as a scour countermeasure downstream of a sluice gate

BackgroundLocal scour is one of the main problems affecting the stability and operation of control hydraulic structures. Many techniques were used to control the resulting scour. In the recent study, a new technique was used to control local scour downstream single-gate hydraulic regulator by using side flow jets. This study aimed to demonstrate the effect of side jets at different angles on the local scour parameters (depth, length, and volume) and energy dissipation in the downstream hydraulic regulator.ResultsA physical model was used to represent the open channel, regulator, and the side jets with different angles. Five flow discharges, four jet angles, and three gate openings were applied through the experiment. The experiment results showed that the presence of side jets had a remarkable effect on the parameters of the local scour hole and energy dissipation. They dissipated more energy of hydraulic jump than in the absence of jets, and consequently, scour hole dimensions were significantly reduced. Regression analysis was used to deduce equations that can predict the development of local scour downstream sluice gate considering the inclination angle of side flow jets under different flow conditions.ConclusionsSide flow jets can be used as scour reducer techniques with the advantages of eliminating the jet clog produced from sediments and suspended solids.

Predicting the scour depth downstream single step broad crested weirs

The main purpose of broad crested weir used in open channels is to raise and control upstream (U/S) water level. The most important problems for downstream of hydraulic structures are the local scour formed at the downstream of hydraulic structures. Scour control process considered as the main objective to ensure safety and economical design of hydraulic structures to prevent any serious failure in the future. In this study, four models of Single-Step-Broad-Crested weirs with different angles were tested under different flow intensity for duration of 6 hours. Acoustic Doppler Velocimeter (ADV) was used to investigate the velocity field. The results showed that, the model C reduces local scour hole volume was about 87.6%, 55.58% and 44.8% and the maximum depth of scour reduced 73.43%, 32.56% and 24.22% as compared with model D at each discharge.