Pier Scour Research Articles

Numerical Investigation of Flow and Scour around Complex Bridge Piers in Wind–Wave–Current Conditions

A sea-crossing bridge is typically constructed in a marine environment with complex piers, and is susceptible to severe scour at the foundation. This study presents a numerical investigation on flow and scour around a complex pier, specifically focusing on a real-world sea-crossing bridge in China. A comprehensive CFD model incorporating hydrodynamic, free surface, sediment transport, and morphological models is employed for numerical modeling. Additionally, a wind shear stress model is considered to accurately simulate wind generation. The validation of the CFD model is achieved through comparison with experimental data of scour around a cylinder, demonstrating its capability to accurately replicate scour morphology and the temporal evolution of scour depth. Subsequently, the validated model is utilized for full-scale simulation of scour around the complex bridge pier under different wind, wave, and current conditions. The results indicate that compared to single piers with uniform cross-sectional shapes, flow patterns around complex piers are much more complicated. Scour predominantly occurs around the first row of group piles, while downstream piles experience less scour due to the sheltering effect from upstream piles. Furthermore, it becomes evident that the current exerts greater influence on pier scour than waves and wind, while the latter two factors primarily influence the superstructure of the bridge.

Probabilistic seismic safety assessment of bridges with random pier scouring

Foundation scour has been a reason for several cases of river-bridge earthquake-induced failure during recent decades. However, practising engineers often do not consider its direct effect on the seismic design procedure of such structures. The cavity around a bridge foundation is a random phenomenon depending on several uncertain parameters. This study provides a probabilistic platform to investigate the effect of random scouring on the seismic performance of a particular bridge. The procedure is implemented on an existing multi-span reinforced concrete bridge. To this end, the Monte Carlo simulation technique is utilised to generate samples of the random variables of the scour model to develop the scour hazard curve. A common type of reinforced concrete multi-span bridge is considered as a model. The Latin hypercube sampling method is employed to generate random scouring scenarios in the finite-element model, including uniform and non-uniform scour. Then, fragility curves are developed utilising cloud dynamic analysis. The results reveal that the scouring pattern is one of the most crucial sources of uncertainty. In most circumstances, uniform scour scenarios are more effective than the average of non-uniform cases. However, in some specific patterns, the effect of non-uniform scouring is dominant.

Channel Bed Deformation around Double Piers in Tandem Arrangement in an S-Shaped Channel under Ice Cover

Flow structure and channel bed deformation caused by double piers in a tandem arrangement under ice-covered flow conditions in a bent channel is more complicated than those around a single pier in a straight channel. Based on experiments in an S-shaped flume, the scouring phenomenon at double piers in a tandem arrangement under an ice cover has been conducted by varying pier spacing distance, bend apex cross section (BACS), and hydraulic parameters. Results show that, under identical hydraulic conditions, the variation trend of the scour depth in the vicinity of double piers in a tandem arrangement in a bent channel is similar to that in a straight channel. The deepest depth of scour holes at the upstream BACS is more than that at piers at the downstream BACS. At each BACS, the effect resulting from the interaction of double piers gradually decreases with the pier spacing distance. Different from the characteristics of local scour at double piers in a tandem arrangement in the straight flume, when the ratio of pier spacing distance to pier diameter (L/D) is more than 15, the horseshoe vortex generated by the front pier has negligible impact on the rear pier, and the maximum depth of scour hole at the rear pier scour hole is about 90% that of the front pier. Also, when L/D is higher than 15, the influence of the rear pier on the front one is negligible, and the scour hole depth at the front pier remains the same. However, this phenomenon occurs when the straight flume’s L/D is greater than 17.

Monitoring Scour at Bridge Piers in Rivers with Supercritical Flows

Bridges crossing rivers wider than 50 m are typically supported by piers. In a mobile riverbed, scour occurs around bridge piers, and it is the main cause of bridge collapses worldwide, especially during floods. While bridge pier scour has been extensively studied, there is still a lack of measuring systems for scour monitoring in the field. In this paper, we present existing devices for scour measurement and analyze their comparative advantages and disadvantages. A study case with a scoured bridge pier in supercritical flow is presented. Results show that supercritical flow patterns previously reported at the laboratory scale also occur in the field. The measured scour supports the hypothesis that supercritical flows, even when having high flow speeds, do not produce higher scour than subcritical flows. A possible explanation linked with the sediment sizes of rivers with supercritical flows is discussed. Further, field measurements of scour around bridge piers are needed to enhance our understanding of this complex and nearly unexplored situation.

Local Scour around Side-by-Side Double Piers in Channel Bends under Ice-Covered Conditions—An Experimental Study

The pier scour process is normally intensified in the presence of an ice cover, which poses risks to the longevity and safety of bridges. In the present study, the impact of the densimetric Froude number, locations, and pier spacing of side-by-side piers on the local scour depth under ice-covered flow conditions were investigated based on clear water scour experiments in an S-shaped laboratory flume. The results demonstrated that the local scour at piers along the convex bank was more substantial than that along the concave bank when other factors stayed identical. The densimetric Froude number clearly has more impact on local scour at piers along the convex bank than that along the concave bank. Different from the mechanism of the pier scour in a straight channel, the scour depth around a pier along the convex bank in the S-shaped flume increases as the distance between two piers (or pier spacing) increases, while it decreases around the piers along the concave bank. Similar scour patterns were observed when the side-by-side piers were installed at different bend apex cross-sections. The maximum local scour depths at piers along the convex bank measured at different bend apex cross-sections were relatively unchanged when other influencing factors were held constant. However, the maximum scour depth around piers along the concave bank decreased as the bends increased toward downstream.

Investigation approaching flow to bridge and prediction of bridge pier scour with floodplain vegetation in compound channels under pressurized flow conditions

The local scouring around the pier, is one of major cause of the bridges failure worldwide. Compared to the flow hydraulics in single channels, the flow pattern in compound channels is completely different with flood plains covered with vegetation and this issue can affect the amount of scouring in the area of bridge piers. However, the combined effect of these factors has not been systematically investigated. Therefore, due to the complex nature of the local scouring phenomenon and the absence one of an accurate prediction model, in this research, an experimental study on the hydraulic characteristics of the flow approaching the bridge deck in compound channels with floodplain vegetation in pressurized flow conditions, has been done. It was found that increasing vegetation density on average will reduce scour depth by 15% for the same floodplain width and relative depth. In free-flow conditions, increasing the vegetation density on average will increase the scour depth. The aim is to develop an optimized model to estimate the bridge pier scour in consideration of the combined effect. The newly developed relationship shows a good correlation coefficient of more than 92% with the experimental data and yielded better results than the previous equations. The finding of this study will have potential applications for the prediction of the bridge pier scour in clear water conditions.

Discrete Analysis of Local Scour Morphology of Bridge Piers Affected by Sediment Storage Dam

In order to solve the prediction and protection problems of local pier scour with a downstream sediment storage dam on non-uniform sand riverbeds in mountainous areas, the Xi’an Chanhe Bridge in China was taken as the research object. Through comprehensive physical model experiments, the influence of sediment storage dam layout on the surrounding water flow and local scour morphology around bridge piers was studied. The relationship between boundary conditions and local scour pit morphology was studied using a discrete analysis model. The research results showed that the inflow rate Q was the most significant factor affecting local scour, and local scour generally developed rapidly within 0.5–1.0 h and then gradually reached a dynamic equilibrium. The maximum depth was located within 0.25B in front of the pier relative to the pier width , and the impact range of local scour behind the pier was [5B, 10B] . The recommended layout of a sediment storage dam has a distance between pier and dam L of [8B,11B] and a dam crest elevation Z higher than that of the original riverbed elevation at the bridge pier, which is [0.4B, 0.5B]. An improved calculation formula for the local scour depth of bridge piers is proposed and verified through experimental measurements to provide a reference for the design and protection of bridge piers with a downstream sediment storage dam.Q

Estimating pier scour depth under combined waves and current using boosting machine-learning models

Estimating pier scour depth under combined waves and current using boosting machine-learning models

Effect of bridge design parameters on multi-hazard performance of river-crossing bridges

River-crossing bridges in seismically active regions are typically susceptible to two natural hazards – earthquakes and floods. For such bridges, design parameters related to piers may play major roles in bridge multi-hazard performance. In this study, the same was explored for key bridge design parameters – the aspect ratio and longitudinal reinforcement ratio of piers and the differential ground elevation between multiple bents. The multi-hazard condition in the southeast of Nepal was considered as the test-bed hazard condition. The regional seismic hazard was represented using a suite of earthquakes generated based on regional seismic design spectra. Due to the flood hazard in the region, expected pier scour of investigated bridges was estimated from 100-year flood discharge (including climate change projection) in the Koshi River, Nepal. Three-dimensional finite-element models of the chosen bridges, with and without scour and with ±10% variations in the stated design parameters, were developed. Fragility and risk curves of the bridges were developed and compared in order to assess the relative influence of the design parameters on bridge performance. It was found that the aspect ratio and longitudinal reinforcement ratio of piers can significantly influence the multi-hazard performance of riverine bridges. The findings also demonstrate how design parameters may be revised to perform risk-targeted multi-hazard design of bridges.

A new model developed by multigene genetic programming for the temporal evolution of bridge pier scour

Forecasting the time development of scour depth at bridge pier foundations is of great significance to mitigate or avoid the potential failure of bridges. Presently, several models have been developed to predict the scour depth at the base of bridge piers in the case of flood events. This study summarizes existing models for the temporal evolution of bridge pier scour and divides these studies into semiempirical models and empirical models, as well as artificial intelligence models. Several experimental data sets collected from previous studies, 665 points in total, are used to develop a new multigene genetic programming (MGGP) model for temporal scour depth at a circular bridge pier. In addition, independent data, 899 points in total, from previous studies and new physical modeling tests are applied to evaluate the behaviours of existing models, as well as the newly developed MGGP model. It is shown that the MGGP model has good prediction capability when compared with existing empirical and mathematical models.

Field Measurements of Bridge Pier Scour in a Curved Channel

Pier scour is the most common cause of bridge failures, so the problem for the erosion of soil surrounding a bridge foundation has attracted extensive attention. The Jiaxing-Shaoxing Bridge (JSB) is located in Jianshan bend of the Qiantang River Estuary (QRE). The special flow structure and bed morphology of the bend makes the scouring characteristics of the piers particularly complex. Based on the results of Multibeam Echosounders for topographic surveying in recent six years, the scouring characteristics of pier foundation of a main navigation channel of the JSB are analysed in this paper. The results show that with the implementation of the reclamation project in the QRE area, the river channel has been gradually narrowed, coupled with the sharp reduction of the sediment entering the sea of the Yangtze River, the river regime swing in the QRE has changed significantly compared with that in the original design stage of the JSB. Under adverse river regime hydrological conditions, the riverbed erosional depth near the bridge is remarkable, and the local scouring depth of the pier is superimposed, which significantly will reduce the minimum elevation of the bed around the pier.

Bridge Pier Scour in Complex Environments: The Case of Chacao Channel in Chile

Chacao channel bridge is located in a tidal channel with highly-energetic hydrodynamics conditions and significant erodibility potential. Once finished, this 2.5 km long cable-stayed bridge will be the largest in South-America. Here we report an integrated procedure to estimate scour around two of its three towers, both located on a relatively complex but different soil matrices. A high-resolution hydrodynamic model based on the Reynolds-averaged Navier–Stokes equations (RANS), physical tests of in situ soil samples in a Rotating Erosion Testing Apparatus (RETA) and empirical formulas for scour estimation are combined to provide a reliable estimation of scour depth under a periodic tidal ebb-flow regime. The relatively homogeneous soil material at the North Tower shows a high susceptibility to hydrodynamic erosion, which is estimated with SRICOS methodology. The Central Tower, in contrast, needs a combined approach based on the current state of the rock, information collected from underwater explorations and theoretical progress made about rock scour in order to reduce the uncertainty of the soils’ substrate. This study reveals that scour estimation for engineering design purposes in complex soils can be achieved with a joined vision of different disciplines and modelling tools for minimizing the uncertainty.

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.

Local Scour Patterns around a Bridge Pier with Cable-Wrapping

The performance of cable flow-altering bed scour countermeasures was experimentally evaluated based on the scour reduction, bed morphology, and the effects on the flow field. An unprotected 40 mm diameter pier was compared to piers protected with spiral cables (2, 4, 6, 8 and 10 mm diameters) wrapped at a 15-degree angle for two-bed sediment sizes with median grain sizes of 0.86 and 1.83 mm, for a cylinder Reynolds number of 7120. The scour depth was reduced by the cables by up to 52 percent compared to the unprotected pier case, a reduction that increased with increasing cable diameter for both sediment beds. Scour depth and sediment deposition varied by sediment size, where the scour hole was up to 45 percent deeper for the finer sediment bed than that of the coarser bed. Velocity and turbulence statistics showed that cables attenuated the flow within the scour hole by diminishing the downflow and horseshoe vortex, whereas in the case of finer sediment, spatially averaged turbulent kinetic energy and Reynolds shear stresses were respectively up to 1.4 and 1.8 times higher for the unprotected pier than the protected pier, resulting in scour depth reduction. The presence of the cable also reduced the vortex shedding frequency in the pier wake as indicated by a Strouhal number of around 0.175. The results demonstrate the potential of cable threading as a flow-altering scour countermeasure to reduce bridge pier scour.

A review of the state of research on bridge pier scour under combined action of waves and current

A review of the state of research on bridge pier scour under combined action of waves and current

Framework for a reliability-based analysis of local scour and its effect on pile response in clay

The analyses of axial and lateral capacity of a pile are significantly dependent on the appropriate estimation of scour depth, while the scour depth estimation procedure is uncertain due to the hydraulic, hydrologic, and geotechnical parameters uncertainty. Work herein is focused on developing a framework for reliability-based pier scour assessment methodology and demonstrate its integration with the concept of Load and Resistance Factor Design (LRFD) approach. Scour factors are proposed based on reliability level (β) and the associated probability of deceedance (POD). Three example applications of axially and laterally loaded pile design approach while including scour factor in the LRFD framework are demonstrated. Based on axial pile capacity analysis, the increase of pile length when the β-based scour assessment is used with the soil resistance factors, was estimated to be 26.5–29.6 % higher compared to using the deterministic scour with soil resistance factor. In the case of lateral pile response analysis, as β is increased from 2.0 to 3.0, the lateral pile head deflection increased by 46–132 % compared to the deterministically-estimated scour depth case. To obtain β= 3.0 for the considered example while maintaining the pile length unchanged, the pile diameter needed to be increased by 35.7 % compared to the base case pile’s diameter.

Influence of Dynamic Woody Debris Jam on Single Bridge Pier Scour and Induced Hydraulic Head

A woody debris jam around a bridge pier causes a change in flow structure and results in additional scour and an increase in the hydraulic head upstream of the pier, threatening its stability and safety. In the present paper, the spatio-temporal formation of a dynamic woody debris jam formed piece by piece of debris wood was used to investigate the influence of woody debris jams from a life-cycle perspective which included the processes of its formation, growth, failure, and rebirth. Several debris jams were formed in sequence during each experimental test. The results showed that the additional scour generated by the first woody debris jam compared with the scour depth without debris was a function of blockage ratio of the first debris jam, while the influence of the subsequent woody debris jams depended on their dimensions compared with the previous jam. When the subsequent debris jam’s dimensions were larger than the previous one, the scour further increased; otherwise, the scour remained constant and equal to the previous one. In addition, the debris-induced hydraulic head was analyzed and found to be correlated with the Froude number and the debris jam dimensions.

A Fluid-Structure Interaction Model for Bridge Safety Assessment under Scour Conditions

Bridge pier scour engendered by typhoons or flooding poses a threat to the stability, bearing capacity, and other performance parameters of bridge foundations. In traditional static evaluation procedures, linear force distributions are used to express the fluid behavior under current forces, which results in overestimation of stability. A finite element simulation was conducted in this study to correctly evaluate the effect of fluid by developing a fluid-solid interaction (FSI) system. In the FSI system, simulation results for both the fluid and solid systems were exchanged. Thus, the force generated by the fluid system could be incorporated into the solid system to estimate the dynamic response of a pier. A scaled single-pier scour test was first conducted numerically and experimentally. The results showed that the established FSI system can consider the fluid-solid interaction and reflect pier scour behavior accurately. To test the validity of the proposed system, the scour process was numerically conducted on an engineering bridge. Two safety factors were proposed to evaluate the stability of the bridge structure under extreme events such as rainfall or typhoon. The result has proven that the scour stability of the bridge pier can be appropriately evaluated by the proposed system.

Impact of Local Scour around a Bridge Pier on Migration of Waved-Shape Accumulation of Ice Particles under an Ice Cover

The migration of a waved-shape accumulation of ice particles under an ice cover (referred to as “ice wave” in this study) is a phenomenon of transport of ice particles during an ice accumulation process in rivers. The migration of an ice wave will affect the pier scour. On the other hand, the local scour at the pier will affect the migration of ice waves. The interaction between the migration of ice waves and local scour around a pier is a very complicated process since not only the channel bed deforms, but also the ice jam develops simultaneously. By conducting a series of flume experiments, the interaction between the local scour around bridge piers and the migration of ice waves was studied. By applying both continuity and momentum equations, an empirical equation has been derived for predicting the thickness of ice waves around the pier. The impacts of the scour hole on the thickness of ice waves around the pier have been studied. The thickness of the wave crest and the migration speed of ice waves have been investigated. Similar to a scour hole in a sand bed, an “ice scour hole” appeared at the bottom of the ice jam around the pier. The existence of the “ice scour hole” affects the development of ice waves. A formula for calculating ice transport capacity has been obtained. Results calculated using the derived formula are in good agreement with those of laboratory experiments.

Near-Nature Ecological Technique for Pier Scour Countermeasure in a Submerged Overfall

This paper proposes a near-nature ecological technique, which can consist of a wide range of materials, to protect against pier scouring. The proposed technique can involve the use of many long strips that behave like water weeds. This paper studied a protection method against pier scour by using long strips in a submerged overfall, particularly for a pier located at the maximum depth area of overfall scour. The length and size of the strips were chosen as factors to study their protective effect. Our results showed that this approach slowed the flow velocity between the installed strips and bed. The sediment in flow might accordingly move slowly or even settle down. Thus, the pier could be kept stable and safe by the installation of those strips. Experimental results show that the protective effect is more efficient when the strip length is closer to the pier and has a small diameter. Moreover, the maximum protective effect reached 45.5% scour reduction. Varied lengths provided different protective effects against overfall scour. These findings show that this near-nature ecological technique could be a good and economical solution for pier protection in submerged overfalls.