Scour Estimation Research Articles

Turbulence Characteristics before and after Scour Upstream of a Scaled-Down Bridge Pier Model

Bridge pier scour is one of the main causes of bridge failure and a major factor that contributes to the total construction and maintenance costs of bridge. Recently, because of unexpected high water during extreme hydrologic events, the resilience and security of hydraulic infrastructure with respect to the scour protection measure along a river reach has become a more immediate topic for river engineering society. Although numerous studies have been conducted to suggest pier scour estimation formulas, understanding of turbulence characteristics which is dominant driver of sediment transport around a pier foundation is still questionable. Thus, to understand near bed turbulence characteristics and resulting sediment transport around a pier, hydraulic laboratory experiments were conducted in a prismatic rectangular flume using scale-down bridge pier models. Three-dimensional velocities and turbulent intensities before and after scour were measured with Acoustic Doppler Velocimeter (ADV), and the results were compared/analyzed using the best available tools and current knowledge gained from recent studies. The results show that the mean flow variable is not enough to explain complex turbulent flow field around the pier leading to the maximum scour because of unsteady flows. Furthermore, results of quadrant analysis of velocity measurements just upstream of the pier in the horseshoe vortex region show significant differences before and after scour.

Performance of Existing Methods for Estimation and Mitigation of Local Scour around Bridges: Case Studies

AbstractBridge scour is a phenomenon that describes the loss of riverbed sediments around bridge supports because of flow, and it has been identified as one of the leading causes of bridge failures...

Meta-heuristic Optimization Algorithms for Predicting the Scouring Depth Around Bridge Piers

An accurate estimation of bridge pier scour has been considered as one of the important parameters in designing of bridges. However, due to the numerous involved parameters and convolution of this phenomenon, many existing approaches cannot predict scour depth with an acceptable accuracy. Obtained results from the empirical relationships show that these relationships have low accuracy in determining the maximum scour depth and they need a high safety factor for many cases, which leads to uneconomic designs of bridges. To cover these disadvantages, three new models are provided to estimate the bridge pier scour using an adaptive network-based fuzzy inference system. The parameters of the system are optimized by using the colliding bodies optimization, enhanced colliding bodies optimization and vibrating particles system methods. To evaluate the efficiency of the proposed methods, their results were compared with those of simple adaptive network-based fuzzy inference system and its improved versions by using the particle swarm optimization and genetic algorithm as well as the empirical equations. Comparison of results showed that the new vibrating particles system based algorithm could find better results than other two ones. In addition, comparison of the results obtained by the proposed methods with those of the empirical relations confirmed the high performance of the new methods.

Scour at bridge piers in uniform and armored beds under steady and unsteady flow conditions using ANN-APSO and ANN-GA algorithms

ABSTRACT Precise estimation of the local scour at bridge piers, considering flow unsteadiness and bed non-uniformity is crucial for economic and safe design of bridge piers. This study investigates scour at bridge piers in uniform and armored beds, under steady and unsteady flow conditions, applying feed-forward back-propagation (FFBP) artificial neural network (ANN) combined with evolutionary algorithms, using different data sets. ANN is well suited for complex pattern-sorting problems. However, their practical application is made difficult by the lack of a training algorithm, finding a global optimum weight in a relatively short time. Thus, evolutionary algorithms, including adaptive particle swarm optimization (APSO) and genetic algorithms (GA) are applied as exceptional tools for training and tuning the parameters of the proposed ANN models. Based on the available benchmark test data, the ANN-APSO model (with RMSE = 0.142 and 0.059 and R2 = 0.952 and 0.925 for steady and unsteady flow conditions, respectively) and ANN-GA model (with RMSE = 0.196 and 0.048 and R2 = 0.918 and 0.946 for steady and unsteady flow conditions, respectively) are shown to be superior to FFBP-ANN model (with RMSE = 0.214 and 0.106 and R2 = 0.891 and 0.838 for steady and unsteady flow conditions, respectively). Accordingly, the proposed ANN-APSO model is the best tool to evaluate the scour depth at bridge piers in uniform sediment beds under steady flow condition. It can be seen that the ANN-GA algorithm has the best fitness values compared to those of the ANN-APSO algorithm and the other reported approaches in uniform and armored sediment beds under unsteady flow condition. The developed models provide good approximations of the benefits of an FFBP-ANN combined with GA and APSO algorithms compared with a FFBP model, being superior in precision and time consumption.

A Comprehensive Method of Calculating Maximum Bridge Scour Depth

Recently, the issues of scour around a bridge have become prominent because of the recurrent occurrence of extreme weather events. Thus, a bridge must be designed with the appropriate protection measures to prevent failure due to scour for the high flows to which it may be subjected during such extreme weather events. However, the current scour depth estimation by several recommended equations shows inaccurate results in high flow. One possible reason is that the current scour equations are based on experiments using free-surface flow even though extreme flood events can cause bridge overtopping flow in combination with submerged orifice flow. Another possible reason is that the current practice for the maximum scour depth ignores the interaction between different types of scour, local and contraction scour, when in fact these processes occur simultaneously. In this paper, laboratory experiments were carried out in a compound shape channel using a scaled down bridge model under different flow conditions (free, submerged orifice, and overtopping flow). Based on the findings from laboratory experiments coupled with widely used empirical scour estimation methods, a comprehensive way of predicting maximum scour depth is suggested which overcomes the problem regarding separate estimation of different scour depths and the interaction of different scour components. Furthermore, the effect of the existence of a pier bent (located close to the abutment) on the maximum scour depth was also investigated during the analysis. The results show that the location of maximum scour depth is independent of the presence of the pier bent but the amount of the maximum scour depth is relatively higher due to the discharge redistribution when the pier bent is absent rather than present.

Experimental and numerical investigation of bridge pier scour estimation using ANFIS and teaching–learning-based optimization methods

Studies have shown that the major cause of the bridge failures is the local scour around the pier foundations or their abutments. The local scour around the bridge pier is occurred by changing the flow pattern and creating secondary vortices in the front and rear of the bridge piers. Until now, many researchers have proposed empirical equations to estimate the bridge pier scour based on laboratory and field datasets. However, scale impact, laboratory simplification, natural complexity of rivers and the personal judgement are among the main causes of inaccuracy in the empirical equations. Therefore, due to the deficiencies and disadvantages of existing equations and the complex nature of the local scour phenomenon, in this study, the adaptive network-based fuzzy inference system (ANFIS) and teaching–learning-based optimization (TLBO) method were combined and used. The parameters of the ANFIS were optimized by using TLBO optimization method. To develop the model and validate its performance, two datasets were used including laboratory dataset that consisted of experimental results from the current study and previous ones and the field dataset. In total, 27 scaled experiments of different types of pier groups with different cross sections and side slopes were carried out. To evaluate the model ability in prediction of scour depth, results were compared to the standard ANFIS and empirical equations using evaluation functions including Hec-18, Froehlich and Laursen and Toch equations. The results showed that adding TLBO to the standard ANFIS was efficient and can increase the model capability and reliability. Proposed model achieved better results than Laursen and Toch equation which had the best results among empirical relationships. For instance, proposed model in comparison with the Laursen and Toch equation, based on the RMSE function, yielded 50.4% and 71.8% better results in laboratory and field datasets, respectively.

Estimation of Clear-Water Local Scour at Pile Groups Using Genetic Expression Programming and Multivariate Adaptive Regression Splines

The physical process of scour around pile groups is complex. Due to economical and geotechnical considerations, multiple pile bridge piers have become more common in bridge designs. Various empirical models have been developed to estimate scour depth at pile groups. However, these models are mostly based on the conventional statistical regression approaches and are not able to adequately capture the highly nonlinear and complex relationship between scour depth and its influential factors. In this study, genetic expression programming (GEP) and multivariate adaptive regression splines (MARS) were utilized to estimate clear-water local scour depth at pile groups using the flow, sediment, and pile characteristics. Two combinations of data were used to train the GEP and MARS models. The first combination included dimensional variables (e.g., mean flow velocity and depth, mean grain diameter, pile diameter). The second combination contained nondimensional parameters. Results indicated that GEP and MARS can accurately estimate scour depth. Both models yielded better results when the dimensional data were used. In addition, the MARS model with a root mean square error (RMSE) of 0.0220 m and correlation coefficient (R2) of 0.902 outperformed the GEP model with an RMSE of 0.0285 m and R2 of 0.834. Performance of the GEP and MARS models was compared with that of the existing equations. The comparison showed that both models perform better than the regression-based empirical equations. Finally, a sensitivity analysis showed that pile diameter has the most significant impact on equilibrium scour depth.

Significance of Shape Factor of Obstacle on Local Scour

The main goal of this research was to determine the effect of shape factor of obstacle on local scour. The research aimed at better quantification of local scour depth with respect to obstacle shape and bed material variations. The shape factor has been defined as a ratio of scour of any shape to the scour of circular shape under similar conditions. Four different shapes and five different bed materials were used in the study. The shape factors were computed for all the shapes in each bed material used, and the shape factor for a particular shape was found to remain almost unaffected for different bed materials and the flow parameters. On the basis of this research work, a relation was developed for the estimation of local scour, taking into account the effect of shape factor along with other factors responsible for the scour phenomenon. The model so developed was validated for different bed materials and different obstacle shapes with the help of Breusers model.

PHYSICAL MODELLING OF LOCAL SCOUR AROUND BRIDGE PIER

Accurate estimation of local scour around bridge pier is important for economic and safe design of bridges. Due to the complexity of the phenomenon and weak relationship between laboratory and field data, the conventional method such as laboratory-derived equations may fail in determining the accurate scour depth. In the present study, a new method was developed to determine the temporal variation of scour depth and final scour extension around bridge pier. Accordingly, using the rules of physical modelling for rivers, a simple method was established for physical modelling of local scour around bridge pier. To demonstrate the accuracy of the method, a typical prototype was chosen and the method was applied for determining different dimensions of the model. Based on the sediment density scale, low density sediment with ρs=1.05 kg/m3 was considered in the model for scour experiment. The results of the experiment including temporal variation of scour depth, equilibrium time and scour depth and final extension of scour hole were then scaled up to the prototype. Finally, empirical equations were utilized to predict maximum scour depth for the typical prototype. Results showed that the value of equilibrium scour depth from the present method was in the range of empirical equations prediction.

Blockage correction for pier scour experiments

Commonly used bridge pier scour prediction equations have often employed the quantities of relative coarseness, flow shallowness, and flow intensity to yield a design value for maximum relative scour depth at equilibrium conditions. Predictive methods based on these quantities tend to over-predict scour. Moreover, these equations tend to yield different scour estimates for the same flow conditions. The equations, mostly derived from laboratory estimates of scour, have not considered the influence of the flume sidewall proximity. New experiments are conducted to specifically identify the role of channel blockage on scour. Evaluation of results indicates that the influence of blockage ratio on scour can be described using the value of mean flow velocity along the separating streamline and the ratio of the separation velocity to the critical velocity in the form of new parameter kc. A new scour prediction method is developed and presented.

Potential scour evaluation around piers of historical masonry arch bridges: a case study

Bridge scour could be blamed as one of the main causes of failures in masonry arch bridges. Consequently, foundation settlements due to scour are the most threatening cause of damage for historical bridges because of their hidden nature, the capacity to affect the integrity of the whole bridge and the sensitivity of the arches to displacements. Pier settlements produce the development of cracking mechanisms in the arch barrels which affect the global stability of the bridge and lead to irreversible failures and full collapse. Scour estimation in these bridges is a difficult task because of the geometric complexities and existing different shapes of footings. Many empirical equations as well as laboratory data are presented for prediction of the maximum scour depth in bridge piers; however, an equation that especially describes the scour depth in piers with footings has not yet been presented. The scope of this study is to evaluate the scour in the historical Sio-Se-Pol Bridge in Isfahan, Iran. Constriction scour and local scour are computed and their sum is considered as the total scour in the bridge. Comparison of the computations and laboratory results shows an acceptable correlation. Consequently, the existing equations are precise to estimate such scour depths.

A Simplified Simulation Method for Flood-Induced Bend Scour—A Case Study Near the Shuideliaw Embankment on the Cho-Shui River

The modeling of flood-induced bend scour near embankment toes can provide important information for river engineering, embankment safety warnings, and emergency action management. During the rainy seasons, short-term general scour and bend scour are the most common causes for the failure of reinforced concrete embankments in Taiwan. To gain a deeper understanding of the scouring process near embankment foundations, this study proposed a straightforward and practical method for bend scour simulation. The proposed simulation method is subdivided into three stages: two-dimensional flow simulation, general scour estimation, and bend scour estimation. A new bend scour computation equation is proposed and incorporated into a two-dimensional hydraulic finite-volume model for simulating the evolution of bend scour depth around embankment toes. The proposed method is applied to simulate the temporal evolution of bend scouring near the Shuideliaw Embankment on the Cho-Shui River in Taiwan, where serious failure occurred during the June 2012 monsoon. Field data were gathered using the numbered-brick technique at the Shuideliaw Embankment to demonstrate the accuracy of the proposed method. The results of the bend scour simulations compared reasonably well with field measurements, indicating close agreement in terms of water levels and bend scour depths near the Shuideliaw Embankment. The proposed method was found to quickly estimate the maximum short-term general scour and bend scour depths for further enhancement of the safety of the embankment toe.

Prediction of Maximum Scour Depth Using Scaled Down Bridge Model in Laboratory

Recently, United States faced catastrophic flooding in West Virginia, Texas, Louisiana, Oklahoma, Arkansas, and the flooding resulted in several bridge failures. Among them, bridge scour is one of the main causes behind many bridge failures and financial losses as well as loss of life. Since 1960, a lot of scour research have been done and the several estimation methods were already in the hand of hydraulic engineers. Currently, the issues of scour are once again rising topic because the occurrence of extreme weather events are expected to worsen in frequency. Furthermore, current practice of scour estimation shows over-prediction and sometimes, under-prediction. One possible reason is adding separate estimates of contraction and local scour when in fact these processes occur simultaneously. Another possible reason is these equations are based on the experiments using free-surface flow in idealized-rectangular flumes even though extreme flood event can cause bridge overtopping flow in combination with submerged orifice flow. In this study, experiments were carried out in a compound shape channel using scaled down bridge model in different flow conditions (free, submerged orifice and overtopping flow). Based on the findings from laboratory experiments coupled with widely used empirical scour estimation methods, such as CSU pier scour equation, Melville-Sheppard equation and Ambient pier scour method, we will present a comprehensive way of predicting design scour depth which overcomes problem regarding separate estimation of different scour depths. In addition to develop a procedure for estimating of design scour depth, the mechanism and characteristics of scour process will be investigated and a comparison of these equations will be presented.

A review of bridge scour: mechanism, estimation, monitoring and countermeasures

Scour of sediments around bridge foundations by the stream is the most significant contributing factor for bridge failures. The scour failures tend to occur without prior warning and have led to fatalities and economic loss every year. A significant amount of work has been conducted on bridge scour. Such efforts can be broadly classified into two major categories, namely science driven and engineering driven. The science-driven research focuses on understanding the scour mechanism and aims to explain the cause of scour due to different factors. Meanwhile, engineering-driven research focuses on the estimation, monitoring and countermeasures of bridge scour. This paper presents a comprehensive and up-to-date literature review of bridge scour research and practice. Firstly, a brief introduction is given which includes recent cases of failures caused by bridge scour. Then, both scientific and technical research on bridge scour is reviewed, which are categorized into four aspects: macroscopic and microscopic mechanism, scour depth prediction carried out by experimental and field data, direct and remote monitoring methods and active and passive countermeasures. Finally, a summary is provided covering both experimental and computational methods for scour research. Discussion is also provided on emerging ideas to investigate bridge scour from both science and engineering perspectives.

Evaluation of governing parameters on pier scour geometry

Current scour estimation methods typically over-predict scour, resulting in uneconomical design. This tendency is partly due to the complexity of the scouring process, which indicates that some of its aspects are still not well understood, and can also be attributed to scale effects. Here, experiments are conducted to isolate the influence of relative coarseness (D/d50) and flow shallowness (h/D) on scour depth. For the range of D/d50 in the present study, equilibrium scour depth (dse/D) decreases with increasing D/d50 until a limiting value of D/d50 = 175, after which dse/D ≈ 0.75. Furthermore, dse/D is found to depend on h/D when all other scour influencing parameters are held constant. A revised definition of the densimetric Froude number using the velocity along the separating streamline is shown to have an influential role in scour. An improved scour estimation method employing these parameters is presented and compared with current methods.

Improving the prediction of scour around submarine pipelines

Local scour around seabed oil, gas or water pipelines can critically affect their stability. Accurate estimation of scour around pipelines is therefore a key topic of research for marine engineers. This paper presents results from a numerical study of clear-water scour depth below a submarine pipeline for a range of steady flow conditions. The flow field around a pipeline under scour equilibrium conditions was numerically simulated by solving the Reynolds-averaged Navier–Stokes equations with the standard k–ε turbulence closure. The flow discharge through the scour hole for various flow conditions was then investigated, and the results were used to establish the relationship between the flow discharge and the maximum scour depth. By incorporating the Colebrook–White equation, the bed shear stress was obtained and an iterative method was developed to predict the scour depth around the pipeline. The calculated scour depths using the proposed method agreed well with laboratory measurements, with the average absolute relative error being smaller than that obtained by using previous methods. Therefore, this proposed method can be used to predict the clear-water scour around submarine pipelines with improved accuracy.

Scour in bridge piers on non-cohesive fine and coarse soil

Estimation of scour in bridge piers is necessary for economic and safe design of bridges. Although a large number of mathematical models are available, scour estimation in Indian bridges is done by empirical equation like Lacey in both fine and coarse soil. Total scour depths in piers, founded on fine soil, are estimated in five bridges in India using different mathematical models and are compared with those found by IRC method based on Lacey’s theory. IRC method is found to overestimate scour in all the cases and the error is found to vary between 5 and 275%. Local scour depths in bridge piers founded on coarse soil are observed at five bridge sites in Mississippi river basin in U.S.A. Scour depths observed are compared with those predicted by different mathematical models and also by IRC method. Compared to IRC method, scour in piers founded on coarse soil, governed both by size and gradation of sediments, is found to be significantly less than that in fine uniform soil under all velocity of flow. It is observed that the scour depths predicted by mathematical models are quite conservative and closer to the observed ones.

Mobile Riverbed Scour Downstream of a Piano Key Weir

AbstractIn parallel to their most frequent application as an auxiliary dam spillway, piano key weirs (PKWs) are also installed on low-head barrages in combination with run-off-the-river power plants. Their efficient rating curve, advantageous behavior under driftwood blockage, and the absence of mechanical elements are optimal for the hydraulic conditions associated with these run-off-the-river projects. However, in the absence of technical protection measures, scouring of the riverbed can occur at the downstream foundation. The unhindered scour formation and corresponding ridge generation caused by a PKW are investigated in this paper. Physical model tests were conducted under various conditions, providing a general estimation of the equilibrium scour and ridge dimensions. The maximum scour-hole depth dominates the shape of the hole and of the ridge. It was further shown that the maximum scour slope corresponds to the angle of repose of the sediments on the riverbed. Finally, a comparison of the present ...

A screening method for bridge scour estimation and flood adaptation planning utilizing HAZUS-MH 2.1 and HEC-18

The American Society of Civil Engineers’ 2013 Report Card for the Nation’s Infrastructure indicated that over 10 % of the roughly 670,000 bridges in the USA are structurally deficient with a $120 billion investment over the next 15 years required for mitigation. In addition, the Intergovernmental Panel on Climate Change indicates that the frequency of severe precipitation events is increasing as well as associated flooding. These factors coupled with scour as a leading cause of bridge degradation demonstrate a need to develop screening methods for assessing and prioritizing bridges most deserving of adaptation measures. This paper proposes a method for utilizing FEMA’s HAZUS-MH software along with the United States Department of Transportation’s Hydraulic Engineering Circular 18 scour equations to predict the relative scour impact for a bridge to assist in adaptation prioritization. The estimation method develops a scour factor for a bridge using contraction, pier and abutment scour estimates for a base-year and future-year flood event. The scour factor is then used in conjunction with estimated bridge replacement cost to predict monetary damages for a future flood event. The method was validated using repair cost data for eight bridges located in Davidson County (Nashville), Tennessee, from a severe flooding event in May 2010. An extended case study application was also conducted by applying the methodology to a set of flood-prone bridges in the Little Rock, Arkansas area. The results of this research suggest that the proposed methodology may offer municipalities a useful screening tool for prioritizing bridges for adaptation planning.

Ultrasonic P-Wave Reflection Monitoring of Soil Erosion for Erosion Function Apparatus

Abstract Erosion of soils in river, lake, and seabeds is an important component for scour estimation and design of underwater structures. This is because the scour can cause severe structural damage to underwater foundations or embankments. The erosion function apparatus (EFA) method is widely used to estimate the erosion rate of soils in the laboratory, where a soil protrusion of 1 mm thick is exposed to water flow and the time taken to erode this protrusion is measured. However, determining this erosion time is a difficult task because it is only visually inspected, and this can cause considerable measurement errors. Therefore, this study explored the feasibility of using an ultrasonic P-wave reflection monitoring method to more quantitatively assess the erosion rate that otherwise has been measured by visual inspection. The erosion rates were monitored using ultrasonic transducers mounted above a soil surface during the EFA testing on the prepared soil samples containing different clay fractions. Via the P-wave monitoring results, several important semi-quantitative observations were made: an increase in erosion resistance with an increase in the clay fraction, a discontinuous erosion behavior of fine-grained soils with sudden removal of soil lumps by water flows, a continuous erosive action of coarse-grained soils, and inherent heterogeneous erosion even at a specimen scale (i.e., the scale of milli-to-centimeter). While both the P-wave monitoring method and the visual inspection showed similar estimation on the erosion rate, the former was found to provide overall better quantitative assessment, particularly in conditions of very slow or rapid erosion and in the conditions with high turbidity water, unevenly eroded sample surfaces, or limited control on the soil protruding thickness.