Abutment Scour Research Articles

Effectiveness of Collars and Hooked-Collars in Mitigating Scour around Different Abutment Shapes

Abutment scour is a major cause of bridge failures worldwide, leading to disruptions, economic losses, and loss of life. The present experimental study examines countermeasures against abutment scour using hooked-collar protections on vertical-wall and wing-wall abutments (at 45° and 60°) under different flow conditions. All 60 experiments were performed under sub-critical flow conditions by investigating scour around an abutment 20 cm long, 20 cm wide, and 25 cm tall. Two distinct values of the Froude number, 0.154 and 0.179, and a sediment particle diameter (d50) of 0.88 mm were used throughout the experimental phase. The resulting equilibrium scour around the abutments was compared to those with collar and hooked-collar protections. It was determined that the maximum abutment scour depth reduction was 83.89% when hooked collars were placed on vertical wall abutments beneath the bed surface level, and for wing-wall abutments at 45° and 60°, it was 74.2% and 73.5%, respectively, at the bed surface level. Regression analysis was conducted to assess the non-dimensional scour depth (Ds/Yf) and scour reduction (RDs/Yf), with a high enough coefficient of determination (R2 values of 0.96 and 0.93, respectively), indicating high confidence in the analysis. The sensitivity analysis findings demonstrate that the width of the collar (Wc) and La are the most influencing factors affecting Ds/Yf and RDs/Yf.

Bankline Abutment Scour in Compound Channels

This paper presents the results of bed scouring near an abutment that spans the entire floodplain width and terminates at the edge of the main channel, termed here as the bankline abutment. The cross section can be divided into a scoured section and an un-scoured section. The scoured bed profile can be approximated using a power function. An analytical method has been suggested to predict the maximum scour depth at bankline abutment. This method is valid irrespective of whether the original bed is at or below the threshold condition of sediment motion. The proposed method is consistent with the experiments from this study and previous studies.

Location and Extents of Scour Hole around an Erodible Spill-through Abutment under Clear Water Condition and the Abutment Classification

Bridge abutment scour is a complex phenomenon, which significantly affects bridge stability and is responsible for the damage and failures of many bridges over waterways across the world. Given the widespread and devastating human and societal costs, numerous experimental studies have been conducted to find the mechanisms of bridge abutment scour, and several empirical and mathematical prediction models are available. However, the location of the scour hole and its extents have not been investigated in detail, which is one of the important parameters, not only for the bridge stability itself, but also for the safety of structures around the bridge and their design. Thus, in this study, laboratory experiments were carried out using several different lengths of erodible abutment under different flow conditions to suggest a new mathematical criterion for abutment classification with respect to the location of scour holes. Furthermore, additional analysis was conducted to locate the point of the deepest scour depth and extent of the scour hole around the abutment. Both in transverse and flow direction, the location of the scour hole and the point of the deepest scour are governed by the geometric contraction ratio. This research will be useful in analyzing the bridge safety itself as well as safety of the river training works close to the bridge with respect to the location and extents of the scour hole.

Prediction of scour depth around bridge abutments using ensemble machine learning models

Abutments are the structures that support the ends of a bridge deck. Scouring of streambed is a significant problem and ultimately results in the failure of the bridge when the abutments are exposed to flowing water over the long term. Abutment scour is influenced by the type of abutment, shape, and size of the abutments. In the current study, machine learning (ML) models have been utilized for predicting the scour depth around abutments making use of experimental data. The scour depth was modeled around three types of abutments: a vertical wall, a semicircular wall, and a 45° wing wall. Five input parameters, namely, the length of the abutment (L), breadth of the abutment (B), sediment size (d50), approaching flow depth (h) and average approaching flow velocity (U), were used in this study. For predicting the abutment scour depth, ML models such as Adaptive Neuro-Fuzzy Inference System (ANFIS), Gradient Tree Boosting (GTB), Group Method of Data Handling (GMDH), and Multivariate Adaptive Regression Splines (MARS) were applied. Statistical metrics such as Mean Absolute Error (MAE), Root Mean Square Error (RMSE), Relative RMSE (RRMSE), Normalized Nash–Sutcliffe Efficiency (NNSE), Kling-Gupta Efficiency (KGE), and Willmott Index (WI) have been employed to evaluate the performance of each model. It was found that the GTB model provided relatively accurate predictions of the scour depth around the semicircular and 45° wing wall abutments with good metrics. Similarly, the MARS model outperformed all other models in terms of predicting vertical wall abutment scour depth.

Numerical Simulations of Scour around Vertical Wall Abutments with Varying Aspect Ratios under Combined Waves and Current Flows

The present study employs numerical simulations to investigate vertical wall abutment scour with different aspect ratios (B/L, where B is the abutment length in the flow direction, and L is the abutment length transverse to the flow direction) under the combined effect of waves and current. The numerical model solves the Reynolds-averaged Navier–Stokes (RANS) equations and incorporates the Exner formulation to account for bed-level changes. The utilization of the Level Set Method (LSM) in the present numerical model enhances the accurate tracking of free surface and sediment bed. The numerical model validation was performed using a truncated numerical wave tank. The validated model was utilized to examine scour around vertical wall abutments with varying aspect ratios under different wave-current flows. The highest and lowest abutment scour depths were observed for aspect ratios of 0.5 and 2, respectively, in both steady current and the combined effects of waves and current. The vertical wall abutment of aspect ratio 0.5 had a maximum normalized equilibrium scour depth (S/B, where S is equilibrium scour depth), primarily attributed to a sharp edge, leading to increased turbulence and forming a strong primary vortex. The results suggest that the increase in the aspect ratio of the vertical wall abutment decreases the normalized equilibrium scour depth (S/B). According to the authors’ knowledge, this study is the first of its kind that utilizes a three-dimensional, semi-coupled model to examine combined wave- and current-flow-induced scour at vertical wall abutments with varying aspect ratios.

Experimental and numerical modelling of scour at vertical wall abutment under combined wave-current flow in low KC regime

The present study investigates the scour at vertical-wall abutments under a strong current-dominated combined wave-current and current-only environment using experiments and computational fluid dynamics (CFD) modeling. The CFD modelling is performed using an open-source three-phase numerical model (REEF3D), which solves Reynolds-Averaged Navier Stokes (RANS) equations with k-ω turbulence closure. The CFD model is first validated using the experiments and then used for further investigation. The Exner equation was used to compute alterations in bed elevation, while the Level-Set method recorded the free surface and bed topography in a realistic manner. The experimental findings demonstrate that the initial phase of scour development is more rapid under combined wave-current flow, but the equilibrium scour depth is higher in current-only conditions. The increase in Keulegan Carpenter (KC) number increases the scour depth at vertical-wall abutments for a specific relative flow velocity (Ucw). In contrast, a mild increase in vertical-wall abutment scour depth is observed with an increase in Ucw. To the best of the authors’ knowledge, the present work is the first of a kind of experimental and three-dimensional CFD study that estimates abutment scour under strong current-dominated combined wave-current flow.

A novel-tuned Custom ensemble machine learning model to predict abutment scour depth in clear water conditions

Abstract Most bridge failures occur due to the development of scour holes around the abutment and pier. Therefore, accurate prediction of abutment scour depth is critical for designing and maintaining bridges to ensure their safety and longevity. Traditional methods for predicting abutment scour depth, such as empirical formulas and physical models, have accuracy, applicability, and cost limitations. Machine learning (ML), on the other hand, has the potential to overcome these limitations by leveraging large amounts of data and identifying complex patterns and relationships that are difficult to detect using traditional methods. ML models can be trained on various data sources, including field measurements, laboratory experiments, and numerical simulations, to predict abutment scour depth accurately. Therefore, the present study aims to develop a novel-tuned Custom ensemble ML model for predicting abutment scour depth in clear-water conditions. The proposed Custom ensemble model outperforms the ML models used to predict non-dimensional scour depth at abutments with an accuracy of 95.93%.

Effects of collars on local scour around semi-circular end bridge abutments

The occurrence of scour around bridge elements due to the transportation of bed material during flood events can cause serious structural damage and loss of life. Increased uncertainties in precipitation and runoff predictions due to climate change make this phenomenon more complex and dangerous. Bridge scour countermeasures should thus be more focused on decreasing scour formation around bridge elements. In this study, abutment scour under clear-water conditions with constant flow intensity was conducted and collars were tested as scour countermeasures around semi-circular end bridge abutments. The experimental study was performed in a rectangular channel with an almost uniform cohesionless bed material for 3 h with and without collars. Collars of various lengths located at different elevations around the abutments were tested to investigate the effect of collars on scour development. The results of the study showed that the scour depth decreased with increasing collar width and when the collar was placed below the bed level for a given abutment length. The results were compared with those of similar earlier studies to show the effect of abutment shape, size of the bed sediment and test durations on the development of scour depth around abutments.

Local scour around bridge abutments: Assessment of accuracy and conservatism

More than 80 percent of the bridges in the United States are built over waterways. The support systems of the structures crossing waterways are subjected to scour during their service life owing to the flowing water-induced bed shear stresses, resulting in scour. Work herein is focused on characterizing the error associated with three abutment scour prediction models included in the Hydraulic Engineering Circular No. 18. An abutment scour database is utilized to quantify the predicted versus the measured scour depth relationship. Abutment scour prediction models are assessed in terms of two statistical parameters, termed herein Mean Absolute Percentage Error (MAPE, as a measure of accuracy of the prediction), and Level of conservatism, (defined as percentage of cases for which the predicted scour exceeded the measured scour.) For scour associated with vertical wall and spill through abutments, responses to long abutment, and intermediate abutment are examined separately. For vertical wall abutments, conservatism ranged from 4.76% to 100%, and MAPE ranged from 44% to 201%. For spill through abutments, conservatism ranged from 0% to 100%, and MAPE ranged from 10.3% to 347%. Comprehension of the accuracy and conservatism of the deterministic models considered herein contributes to understanding the limitation of the scour depth prediction models.

Combination of Riprap and Submerged Vane as an Abutment Scour Countermeasure

Scour is one of the main causes of hydraulic structural failures. The present experimental study examines the use of riprap, submerged vanes, and a combination of these for scour reduction around vertical walls and spill-through abutments under clear-water conditions. Specifically, the influence of placing riprap stones with different apron shapes (geometry) and/or a group of submerged vanes of constant height and length on abutment scour was examined. The main aim is to propose the optimum apron geometry and placement of submerged vanes to (1) reduce edge failure at vertical walls and spill-through abutments; and (2) prevent shear failure at the spill-through abutment (no shear failure is observed around the vertical wall abutment). The results show that using ripraps for scour protection is more effective than submerged vanes. However, the highest reduction in scour depth was achieved when a combination of riprap and submerged vanes was used together. This arrangement can reduce the maximum clear-water scour depth by up to 54% and 39% with vertical walls and spill-through abutments, respectively. Furthermore, selecting appropriate apron scale ratios reduces the required riprap volume by up to 46% and 31% for the vertical wall and spill-through abutment, respectively. In addition, the installation of vanes increased the riprap stability and reduced edge failure in both abutments tested. Finally, using riprap aprons with proper scales ratios at the downstream side of the spill-through abutment also prevents shear failure in this zone.

The study of the local scour behaviour due to interference between abutment and two shapes of a bridge pier

Although the complexities and irrevocable consequences associated with bridge scour have attracted researchers interest, their studies scarcely indicated the effect of a bridge pier proximity to an abutment. This research aims to measure maximum scour depth and exhibit the impact of pier-abutment scour interference based on laboratory experiments where vertical-wall abutment and two shapes of a pier (oblong and lenticular) were used at three different spacings (23.5, 16.0, 9.0 cm). The results showed an obvious increase in the scour depth ratio when increasing flow intensity, Froude number, and a decreasing flow depth. They also showed that reduced pier-abutment spacing was accompanied by increase in pier scour for both shapes while decrease in abutment scour. The maximum scour depth that caused by an oblong shape was more than a lenticular shape by about 10.8%. Furthermore, new empirical equations were derived using IBM SPSS Statistics 21 with determination coefficients of 0.969, 0.974, and 0.978 for oblong, lenticular and abutment, respectively. They showed the correlation between predicted and observed data.

Use of spur dikes with different permeability levels for protecting bridge abutment against local scour under unsteady flow conditions

Local scour around abutments is one of the most important reasons for a bridge collapse, making it a major concern for hydraulic and river engineers. Available studies on scour control around abutments have been limited to steady flow conditions. In this light, the present experimental study investigates using a single spur dike with different levels of permeability (0%, 35%, 50%, and 65%) to reduce scour around a short vertical-wall abutment (abutment length/flow depth ≤ 1) under unsteady flow conditions. The hydrographs with Gaussian distribution and different base flow times (i.e., duration of 15, 30, 60, and 90 min) were used to simulate the unsteady flow. Abutment scour depth variations with time showed that the final scour depth always appeared after the peak discharge of the hydrograph regardless of whether a spur dike was used. It was shown that the spur dike has successfully reduced local scour around the abutment. The maximum depth of scour hole around abutment was reduced by 47%, 32%, and 11%, when spur dikes with 35%, 50%, and 65% permeability were, respectively, used. Using an impermeable spur dike not only prevented the scour upstream nose of the abutment but also led to some deposition that raised the bed level by nearly 0.47 La (where La is the abutment's length) in that area. However, the maximum depth of scour hole around the impermeable spur dike was nearly identical to that occurred around the abutment for the experiments without a spur dike, making it necessary to arrange for scour protection around the spur dike.

Investigation on vertical wall abutment scour under steady and unsteady flow in compound channels

Investigation on vertical wall abutment scour under steady and unsteady flow in compound channels

Experimental study: scour interference between vertical-wall abutment and two shape of bridge piers

Local scour considered as one of the main hazard factors that damaging bridges and in order to understand and controlling this problem, numerous researchers investigated its impact around pier or abutment in isolation but few take into account the consequences of pier proximity to abutment. This study aims to show the effect of pier-abutment scour interference. Under clear-water conditions, laboratory experiments were conducted utilizing vertical-wall abutment and two shape of pier (rectangular and ogival) at three different spacing (23.75, 16 and 9cm), and the influence of other parameters on reducing scouring process were also investigated. Approximately all results showed the increasing in pier scour depth with decreasing in abutment scour depth when reducing the spacing between them, where the maximum pier readings of scour depth was recorded at the smallest spacing. Also, scour increased with increasing flow intensity, Froude number and decreasing flow depth. Moreover, the maximum scour depth caused by rectangular shape was more than ogival shape by percentage about 11%.

A comparison between advanced hybrid machine learning algorithms and empirical equations applied to abutment scour depth prediction

Complex vortex flow patterns around bridge piers, especially during floods, cause scour process that can result in the failure of foundations. Abutment scour is a complex three-dimensional phenomenon that is difficult to predict especially with traditional formulas obtained using empirical approaches such as regressions. This paper presents a test of a standalone Kstar model with five novel hybrid algorithm of bagging (BA-Kstar), dagging (DA-Kstar), random committee (RC-Kstar), random subspace (RS-Kstar), and weighted instance handler wrapper (WIHW-Kstar) to predict scour depth (ds) for clear water condition. The dataset consists of 99 scour depth data from flume experiments (Dey and Barbhuiya, 2005) using abutment shapes such as vertical, semicircular and 45° wing. Four dimensionless parameter of relative flow depth (h/l), excess abutment Froude number (Fe), relative sediment size (d50/l) and relative submergence (d50/h) were considered for the prediction of relative scour depth (ds/l). A portion of the dataset was used for the calibration (70%), and the remaining used for model validation. Pearson correlation coefficients helped deciding relevance of the input parameters combination and finally four different combinations of input parameters were used. The performance of the models was assessed visually and with quantitative metrics. Overall, the best input combination for vertical abutment shape is the combination of Fe, d50/l and h/l, while for semicircular and 45° wing the combination of the Fe and d50/l is the most effective input parameter combination. Our results show that incorporating Fe, d50/l and h/l lead to higher performance while involving d50/h reduced the models prediction power for vertical abutment shape and for semicircular and 45° wing involving h/l and d50/h lead to more error. The WIHW-Kstar provided the highest performance in scour depth prediction around vertical abutment shape while RC-Kstar model outperform of other models for scour depth prediction around semicircular and 45° wing.

Investigation on vertical wall abutment scour under steady and unsteady flow in compound channels

Investigation on vertical wall abutment scour under steady and unsteady flow in compound channels

An Experimental Study on the Effects of Debris Accumulation at the Culvert Inlet on Downstream Scour

The major damage of hydraulic structures at river crossing occurs during floods and culverts is the structure which use as a part of drainage system in ephemeral streams. Failure in structures is caused for different reasons but pier and abutment scour is the main reason. The presence of debris causes larger scours and sediment removal compared to the absence of debris accumulation. In this study, the common problem of the flow blockage at culvert inlets is investigated applying a hydraulic model set in laboratory. Experiments were performed to understand the changes and interaction of scour depth over a range of downstream flow depths, ht and densimetric Froude number, Fo. The debris accumulation is modelled by rectangular plates of constant width (30 cm) and various heights (4, 8, 12, 16 cm) set at the culvert entrance. When culvert inlet area decreased by the smallest solid debris accumulation - which covered 20% of inlet area-, the upstream water level raised up to 12% and by the biggest solid debris size- which covered 80% of inlet area- water level increased up to 60%. Debris accumulation causes larger scours and sediment removal, so the scour hole area extended extremely in flow direction. A new maximum scour depth predictor equation has been proposed to predict the effects of debris accumulation at culvert inlet on downstream scour. This equation is well fitted with the experimental results of the current study and the results of experiments from the previous studies used to analyze presented formula.

Computational fluid dynamics modeling of abutment scour under steady current using the level set method

The scour and deposition pattern around an abutment under constant discharge condition is calculated using a three dimensional (3D) Computational Fluid Dynamics (CFD) model. The Reynolds-Averaged Navier Stokes (RANS) equations are solved in three dimensions using a CFD model. The Level Set Method (LSM) is used for calculation of both free surface and bed topography. The two-equation turbulence model (k-ε and k-ω) is used to calculate the eddy viscosity in the RANS equations. The pressure term in the RANS equations on a staggered grid is modeled using the Chorin's projection method. The 5th order Weighted Essentially Non-Oscillatory (WENO) scheme discretizes the convective term of the RANS equations. The Kovacs and Parker and Dey formulations are used for the reduction in bed shear stress on the sloping bed. The model also used the sandslide algorithm which limits bed shear stress reduction during the erosion process. The numerical model solution is validated against experimental results collected at the Politecnico di Milano, Milan, Italy. Further, the numerical model is tested for performance by varying the grid sizes and key parameters like the space and time discretization schemes. The effect of varying bed porosity has been evaluated. Overall, the free surface is well represented in a realistic manner and bed topography is well predicted using the Level Set Method (LSM).

Six legged concrete (SLC) elements as scour countermeasures at wing wall bridge abutments

ABSTRACT Previous research studies have shown that abutment scour makes a major contribution to bridge failures. Protecting bridges against scour is, therefore, a priority need. For existing bridges, armouring methods, such as riprap, have a wide application. In the areas where providing stones is expensive, concrete blocks or similar techniques are often used. In the present study, the application of the Six Legged Concrete (SLC) elements was experimentally investigated. The SLC elements were placed in three different densities (open, medium and dense) at three different placement depths (h/l = 0, 0.5 and 1; where h is the element installation height above the bed and l is element height). Each alternative was tested under different flow conditions for a wing-wall abutment. In general, the results showed that the SLC elements can considerably reduce the scour under different flow conditions. In an optimal arrangement, the elements reduced the scour depth at abutment nose up to 100%. The maximum reduction of scour depth was obtained when the SLC elements were placed densely on the bed (h/l = 1).

Scour at side by side pier and abutment with debris accumulation

This is the first attempt to study the effect of debris on the scour at side by side pier and abutment. A large set of experimental tests was carried out at the hydraulic laboratory of Shahid Bahonar University of Kerman, in a tilting flume with 10 m length, 0.8 m width and 0.5 m depth. Effect of debris shape, thickness, position, length, and the distance between abutment and pier was investigated. Results revealed that the main factor in deepening and developing of scour hole is the distance between pier and abutment, lp, by increasing the distance, the scour depth primarily increases and then decreases to eventually reach the scour depth at single pier. The observations indicated the significant effect of debris on dimensions of scour hole, for example, increasing the debris thickness and length increased the maximum scour depth up to 30 and 8%, respectively. Based on the measured data, some improvements were made on the existing equations and a set of new relations was presented to estimate the side by side pier and abutment scour depth.HighlightsFlow and scour pattern at side by side pier and abutment were investigated.Effect of debris accumulation on the scour processes was studied.Based on the measured data, improvements were made on the previous equations.New relations were proposed to predict side by side pier-abutment scour depth.