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This paper studied the scour around bridge piers by conducting laboratory experiments and numerical simulation using Sediment Simulation In Intakes with Multiblock option (SSIIM) program. Six pier models were investigated under different flow conditions in sandy soil for two cases: piers with and without a protective plate (collar). The models were arranged as follows: one pier, two piers side by side, two piers tandem, three piers triangular (1 × 2), three piers triangular (2 × 1), and four piers square (2 × 2). It was found that the relative scour depth (ds/yt) where ds is the local scour depth and yt is water depth, increases as Froude number (Fn) increases for all models. Two Piers tandem model with a collar significantly reduced scour depth around the piers by over 80% compared to unprotected models. The collars effectively reduced the formation of vortices and minimized the detrimental impact on the sediment around the pier. The simulated results using the SIIM program are consistent with the experimental results, with an error of 10%. Scouring depth relationships were also deduced that are useful in bridge piers protection design in similar cases under the same conditions. [ABSTRACT FROM AUTHOR]

AbstractThis study presents an investigation of the impact of tidal currents on scouring beneath pipelines. To elucidate the role of parameters such as current velocity, time period of each cycle, depth of flow, and number of tidal cycles required to attain equilibrium, 38 tests were conducted in a bidirectional flume for a pipeline. The geometry of pipeline and the flow characteristics of the Persian Gulf were scaled down to a ratio of 1:30 based on the Froud law and used for this study. The tests were carried out in clear water conditions. The experimental findings reveal that a significant portion of the scour depth occurs during the mid-range of each half cycle. This is the case regardless of ebb or flood conditions, and when the current velocity is at its maximum value. Also, the scour hole resulting from bidirectional flow exhibits a symmetrical shape with two dunes on either side. Furthermore, the relative scour depths in daily and semi-daily tidal tests are greater by factors of 1.40 and 1.1, respectively, compared to unidirectional tests when the root mean square values from steady current scenarios are considered. Finally, a series of formulae have been developed based on the experimental results. [ABSTRACT FROM AUTHOR]

In this study, different geometrical configurations of T-head spur dikes, such as spur dike length (l = 6, 9, and 12 cm), wing length (λ = 0.5, 0.75 l, and l), and wing orientation (θ = 60°, 90°, and 120°) are used to investigate the local scour. The T-head spur dike with l = 9 cm, λ = l, and θ = 90° is found as the optimum configuration. The turbulent kinetic energy flux in the vertical direction is positive in the non-scour zone and negative in the scour zone with a higher magnitude, resulting in the transport of turbulent energy towards the bed that leads to scouring. The sweep events dominate against the ejection events in the scour zones, but in the non-scoured zone, it is the opposite. A regression equation was developed to estimate the scour depth around the spur dike, and satisfactory results were obtained. [ABSTRACT FROM AUTHOR]

AbstractScour occurs inevitably around monopiles of offshore wind turbines (OWTs), negatively impacting the operation of the turbines. For the purpose of ensuring the long-term safety and stability of the foundations, solidified soil which provides higher scour resistance can be used to remediate scour considering its technical convenience. In this study, flume tests were conducted under unidirectional flow conditions to investigate the dynamic remediation of the local scour hole, which was applied to different scour development processes, using solidified soil. Various remediation schemes were simulated by controlling the design elevation of the solidified soil layers to investigate their performance under different conditions. Meanwhile, the phenomenon and characteristics of edge scour during remediation were also analyzed. Results show that different remediation elevations and initiation would lead to varying degrees of edge scour. Early remediation costs less solidified soil but results in severe edge scour, while late remediation needs more materials and experiences milder edge scour. In addition, an evaluation method assessing solidified soil remediation was established. This method was utilized to evaluate the comprehensive benefit and edge scour risk for different remediation schemes. [ABSTRACT FROM AUTHOR]

Understanding the scour process around bridge piers and investigating approaches to reduce these phenomena is an important issue for engineers. Side-by-side piers cause lower scour depth compared to a single pier with the same diameter. In this study, the application of downstream bed sill and continuous footing to control the scour depth around single piers and two side-by-side piers is investigated experimentally. The results show that by using a continuous footing with a thickness equal to the pier diameter, the scour depth in front of the pier is reduced by 50% and 55% for single pier and side-by-side piers, respectively. Moreover, when the continuous footing thickness is doubled, no scour depth is observed in front of the pier. Additionally, incorporating a downstream bed sill adjusted to the pier results in a reduction of approximately 30% in scour depth in front of the piers. [ABSTRACT FROM AUTHOR]

This study examines the scouring effect downstream of a type-A trapezoidal stepped Piano key weir using experimental methods. The experiments were performed on weirs, both with and without steps at the outlet keys, while considering various discharge rates, tailwater depths, and bed material sizes. The study scrutinized three unique weir configurations, each with different dimensions and step counts at the outlet keys: the first, second, and third weirs had 5, 10, and 15 steps respectively. The findings indicate that the maximum scour depths in the Piano key weirs with 5, 10, and 15 steps were, on average, 17.5%, 31%, and 19% less than those in the non-stepped weir. It was also noted that an increase in discharge and a decrease in tailwater depth and bed material size led to an increase in the maximum scour depth. Moreover, an increase in the number of steps and a decrease in the size of the bed materials resulted in a reduction in sediment ridge height. The analysis suggests that the average scour index values in the 10-stepped weir were about 21% lower compared to the non-stepped weir. These insights contribute to the design and optimization of hydraulic structures to effectively mitigate scouring effects. [ABSTRACT FROM AUTHOR]

Recent catastrophic tsunamis, such as the 2004 Indian Ocean and 2011 Tohoku events, have underscored the need for resilient coastal infrastructure. Field investigations in the aftermath of these tsunamis have consistently identified local scour around structures as a critical factor contributing to their failure. Local scour refers to the erosion or removal of sediment in the vicinity of a structure, triggered by the unsteady water flow associated with tsunami inundation. The recognition of the significance of this phenomenon, juxtaposed with the current deficiency of detailed and systematic design guidelines that incorporate the ramification of local scour, has spurred advancements in this area of research. This study has meticulously reviewed state-of-the-art studies on tsunami-induced local scour around structures. The existing design guidelines have been critically assessed, pinpointing their limitations and areas that require further elucidation. Moreover, this critical analysis delineates the current knowledge gaps and outlines prospective directions for future research endeavors aimed at enhancing the resilience of coastal infrastructure, with a particular focus on mitigating the effects of local scour. This comprehensive review aims to deepen the understanding of tsunami-induced local scour and promote more effective, evidence-based design strategies to mitigate the risk of structural failure in high-risk coastal areas. [ABSTRACT FROM AUTHOR]

Hydraulic structures at river crossings, especially culverts in ephemeral streams, are susceptible to damage during floods due to culvert scour, caused by various factors. It is essential to implement preventive measures to ensure the longevity and safety of these structures. This paper aims to present a comprehensive review of the factors influencing local scour downstream of culverts, offering a thorough understanding of this phenomenon. Consequently, a thorough review of the experimental studies and their corresponding outcomes documented in the literature is conducted. The analysis is divided into two main sections. The first section discusses dimensional analysis, while the second section delves into the key parametric factors affecting scouring, including flow regime, scour time, and experimental studies documented in the literature. The methods used in the second section are categorized into three distinct categories: channel and culvert dimensions, flow conditions, and sediment characteristics. This article not only provides a platform for researchers to conduct laboratory research but also assists hydraulic engineers in identifying crucial factors in culvert design. [ABSTRACT FROM AUTHOR]

Inclined pile foundations are commonly adopted in the support of wharf, harbor, bridge, and wind turbine structures. In the context of offshore wind turbines, inclined piles are typically arranged symmetrically around a circle with an elevated pile cap above sea level, referred to as an elevated pile-cap foundation. However, limited research exists on the impedances of inclined pile foundations with elevated pile caps. In this study, a theoretical model was developed that incorporates a homogeneous soil half-space and an inclined pile foundation with an elevated pile cap. The pile and soil half-space were modeled as Euler-Bernoulli beams and linear-elastic continuum, respectively. The soil's contribution to the pile's dynamics was represented by the receptance matrix, established at discrete interactions points along the pile's embedded section. The effects of the rake angle and scour depth on the dynamic impedances of the inclined pile foundation with an elevated pile cap were investigated. It was observed that the peak frequency of impedance shifts to a lower value as the scour depth increases; whereas the peak frequency shifting effect is less prominent when the rake angle changes. The impedance of the elevated pile-cap foundation is more sensitive to the pile's rake angle compared to the scour depth. [ABSTRACT FROM AUTHOR]

Weirs and gates are hydraulic structures installed in canals, mainly for controlling the discharge. Because of their existence, unfavorable influences regarding the downstream bed configurations were recorded. This study experimentally explores the combined effect of simultaneous flow through a hydraulic device consisting of a V-notch sharped weir with an inverted V-shaped gate, aiming to minimize the downstream bed scour. Eighty-one runs were carried out using nine weir-gate models with three different vertex angles. The tests were executed considering three upstream and three downstream water depths. A V-notch weir with an angle of 120º was tested under similar hydraulic conditions and was used for comparison. The results revealed that the length of backflow was increased by the decrease in weir angle under a fixed 120° gate angle. The bed configurations were sensitive to gate angle. The combined device showed a significant decrease in bed disturbances regardless of the angles used compared to the traditional V-notch weir. Simple formulas were developed to predict the scour parameters. [ABSTRACT FROM AUTHOR]

This paper compares the application of two recently published guidance documents for risk-based assessment of hydraulic actions on bridges, namely the UK Design Manual for Roads and Bridges and the Italian Ministry of Infrastructure and Transport's Guidelines, to two case study bridges (Staverton Bridge, UK; Borgoforte Bridge, Italy). This work is one of the first to illustrate how to apply these guidelines. Both documents present risk-based methods for the assessment of hydraulic actions, while exhibiting fundamental differences. For example, the UK method prescribes calculations for local and constriction scour, water depth, and velocity at several cross-sections; by comparison, the Italian method does not prescribe calculations to assess the risk level. For the case studies in this paper, the hydraulic risk obtained for Staverton Bridge resulted as 'High' using both methods. The scour score for the Borgoforte Bridge resulted higher using the Italian method (Medium-High), as compared to the UK approach (Medium). This difference is due to how the guidelines assess the vulnerability associated with the minimum clearance. The comparison of these two risk-based approaches and the resulting discussion may serve as a useful resource for those wishing to develop new risk-based methods for assessing hydraulic actions on bridges. [ABSTRACT FROM AUTHOR]

Estimation of local scour depth at a bridge pier must be accurate and precise for the safety assessment of pier foundation. Many deterministic scour depth prediction models for bridge piers in sands and gravels have already been reported in the literature. However, the various types of uncertainties may be involved in the deterministic scour depth prediction models and thus affect the accuracy of the scour depth. To account for such uncertainties, a reliability analysis method is generally adopted. A sizable amount of laboratory and field data on scour has been procured in the present study to assess the performance of existing scour prediction models for gravel beds and develop a probabilistic scour prediction model using a First-Order Reliability Method (FORM) based on the object-oriented constraints optimization spreadsheet algorithm for the most appropriate selected deterministic scour prediction model. A new relationship of the silt factor has also been developed to estimate the scour depth in gravel bed as per Indian Practice. A safety factor based on the target reliability index has also been proposed in this study. [ABSTRACT FROM AUTHOR]

Bridge scour is a leading cause of failure for bridges over waterways and is notoriously difficult to detect with accuracy. Dynamic Structural Health Monitoring (SHM) of bridges for scour has gained traction in recent years as monitoring systems have improved and the reliability of measurements increased. Due to the large number of bridges on typical networks and the limited financial resources within asset management agencies, decision-makers must prioritize certain structures when it comes to management in the event of flooding. The decision to install a dynamic SHM system on a bridge must be balanced by the financial benefit of doing so, as limited resources often need to be carefully rationed. In this paper, a methodology is proposed to evaluate such benefit based on the Value of Information (VoI) from Bayesian decision analysis. A case study is presented whereby a dynamic SHM system is considered to be installed on a typical bridge with the aim to support emergency management operations during flooding. The proposed methodology allows computation of the financial benefit of installing a dynamic SHM system over a certain reference period, thus accounting for multiple flood events and scenarios. The various elements of the procedure are discussed in detail. [ABSTRACT FROM AUTHOR]

Scour is a significant cause of bridge failure, and resulting bridge closures are likely to generate significant disruption to infrastructure networks. The management of scour-susceptible bridges is a significant challenge for improving transport resilience, but tends to be heuristic and qualitative. Such assessments often suffer from insufficient knowledge of key factors and require assumptions, which may increase their estimation and relative uncertainty. Analysis of publicly available technical documents reveals that various definitions of "risk" are adopted, as well as multiple approaches are applied. This paper has three objectives: (i) to illustrate the concept of risk in bridge scour management; (ii) to propose a simple scoring system to analyse existing risk-based approaches to manage bridge scour; and (iii) to analyse and compare such approaches on the basis of the obtained scores. A sample of nine documents containing bridge scour risk assessment practices or approaches was analysed using the developed rating system. [ABSTRACT FROM AUTHOR]

The present laboratory study is done to understand the effect of suction seepage flow on the scour geometry around an abutment placed on non-cohesive bed materials. The experimental data revealed that suction seepage through the channel side and bed affects the scour depth and deposition height. Under the present experimental conditions, it is found that the maximum reduction of scour depth under vertical suction, side suction and combined suction are 37%, 19% and 21% respectively. The results further demonstrate that the reduction of scour depth at the upstream outer nose of the abutment is more under vertical suction, whereas under side suction, the main influence area is closer to the side wall. However, under combined suction seepage, it is found that the reduction of scour depth is in between vertical suction seepage and side suction seepage. Another important finding is that scour reduction increases with increase in seepage rate. [ABSTRACT FROM AUTHOR]

The three-dimensional topography of the seabed has a significant influence on the wave field and the failure characteristics of the sloping seabed. Nevertheless, previous experimental studies were predominantly limited to two-dimensional wave conditions. In this study, a series of regular wave experiments (including a rigid-slope seabed and a sandy-slope seabed) have been done in a large-scale three-dimensional harbor basin to investigate the three-dimensional wave field in the Zhoushan sea area and the response characteristics of the sloping seabed under the wave actions, respectively. The results of the rigid-seabed tests show that the wave field has obvious three-dimensional characteristics under the influence of three-dimensional topography. During the process of propagation, wave shoaling occurs which leads to wave breaking finally. At the same time, the wave will reflect when it meets the topography, and the reflected wave will affect the wave field in turn. The pore water pressure response and three-dimensional failure modes of sandy sloping seabed under the wave actions are obtained by the sandy-seabed experiment. Three-dimensional seabed topography of typical sea area is established in the harbor basin. The characteristics of the three-dimensional wave field and the response of submarine slope under the three-dimensional wave actions were investigated. The three-dimensional topography of sandy sloping seabed after wave actions was captured. [ABSTRACT FROM AUTHOR]

Several countermeasure techniques have been presented to control bridge scour-induced failure. Air-bubble injection, a new method compatible with the environment, was introduced to combat destructive vortices that cause bridge piers to be scoured. Extensive experiments were conducted to determine the appropriate air-bubble injections for the least scours at a bridge pier. Two different clear-water flow intensities with air-bubble injections were assessed in different radial positions around and also on the upstream half of the bridge pier. The vertical position of air injections and air discharge were determined previously to be optimal. The long-term experiments revealed that the well-designed air-bubble injections reduced the local scour around the bridge pier. It was found that the complete air-bubble injection around the bridge pier is the best configuration and able to reduce the scour depth about 44% over the case with no air injection (non-protected pier). Moreover, the appropriate arrangement of bubble injections to lessen the scour depth is the nearest radial position of the injection to the bridge pier and with increasing the radial distance of injections to the pier, the bubble plumes move downstream by the main flow. The results indicate that bubble plumes would be effective in both flow intensity, u*/u*c = 0.7 and 0.9, as examined in the present study. [ABSTRACT FROM AUTHOR]

Rock weirs are low-head river restoration structures. The present study comprised two sets of flume tests (i.e. fixed bed and moveable sand bed tests) to investigate the rock dislodgement process, which is a primary cause of the failure of rock weirs. The impacts of approach flow intensity, submergence, void ratio and scour of bed sediment on rock weir dislodgement, and the responses of sediment bed scour at rock weirs to the rock weir dislodgement, are analysed and discussed. Three limits are defined to classify the amount of the rock weir dislodgement: (1) limit I indicates the incipient dislodgement of rock from downstream weir toe; (2) limit II indicates that a few rocks are dislodged from downstream weir face and weir crest; (3) limit III indicates that large numbers of rocks are dislodged from downstream weir face and weir crest, which leads to weir failure. A predictor of each limit is proposed for rock weir design. [ABSTRACT FROM AUTHOR]

This article proposes a seismic fragility analysis framework of bridges, which considers the freeze–thaw cycles and scour comprehensively. The time-varying seismic fragility analysis method is used to analyse the bridge system based on the degradation law of mechanical properties of concrete under the freeze–thaw cycles, combined with the uncertainty of earthquake, scour depth and freeze–thaw cycles. Under the condition of the scour, with the growth of service time, the seismic fragility of piers and bearings increased and the exceeding probability of bearing is higher than the pier, which makes the bearing more easily damaged than the pier in the case of an earthquake, thus reduces the seismic damage of the pier. The plastic hinge of the bridge pier transfers from the immersion zone to the freeze–thaw zone in freeze–thaw cycles. In this process, the curvature in the freeze–thaw zone grows up, dissipates seismic energy and leads the pier's fragility to decrease before the plastic hinge transfer. When combined with the scours and freeze–thaw cycles, the failure probability of the pier is slightly lower than that of only the scour action due to the phenomenon of plastic hinge transfer. [ABSTRACT FROM AUTHOR]

Various protective methods are incorporated in order to change the flow pattern and reduce the intensity of the vortices around the piers with the aim of reducing scour at bridge piers. One of these methods is the employment of submerged vanes at the upstream side of the bridge piers. This study investigated the effect of the submergence ratio of the submerged vanes in scour reduction around a single pier and a group of piers. The results indicated that the greatest reduction in the maximum scour depth, the scour hole volume, the maximum sedimentary bar, and the scour hole area around the piers occurred in experiments with a single pier and triad piers with a longitudinal direction in combination with 75%-submerged vanes. At this submergence ratio, the maximum scour depth and the scour hole volume decreased by nearly 30 and 59% respectively in the single pier test including the submerged vanes, and by nearly 23 and 37% respectively in the triad pier group test with a longitudinal direction including the submerged vanes in comparison to the test with no submerged vane installed. [ABSTRACT FROM AUTHOR]

The changing climate with resulting more extreme weather events will likely impact infrastructure assets and services. This phenomenon can present direct threats to the assets as well as significant indirect effects for those relying on the services those assets deliver. Such threats are path-dependent and place-specific, as they strongly depend on current and future climate variability, location, asset design life, function and condition. One key question is how climate change is likely to increase both the probability and magnitude of extreme weather events under different scenarios of climate change. To address this issue, this paper investigates selected effects of climate change and their consequences on structural performance, in the context of evolving loading scenarios in three different continental regions: Europe, North America, and Asia. The aim is to investigate some main place-specific changes of the exposure in terms of intensity/frequency of extreme events as well as the associated challenges, considering some recent activities of members of the IABSE TG6.1. Climate change can significantly affect built infrastructure and the society by increasing the occurrence and magnitude of extreme events and increasing potential losses. Therefore, specific relationships relating hazard levels and structural vulnerability to climate change effects should be determined. [ABSTRACT FROM AUTHOR]

This paper is aimed to investigate the temporal variation of scour depths and bed topography in the presence of a group of six vertical and inclined piers placed in a 180-degree bend flume. For this purpose, a series of tests were performed in a test flume provided by Hydraulics Laboratory of Persian Gulf University, Bushehr, Iran. The piers were placed at the angle of 60-degree of the bent flume. The flume was 1 m wide and the ratio of curvature to the width of 2 and has two straight sections at its upstream and downstream with 6.5 m and 5.1 m length, respectively. The results showed the temporal evolution of scour depth was decreased with the passage of time. The location of the maximum scour depth was time dependent so that as the experiment progressed, it moved from the vicinity of the inner bank to the middle of the flume and eventually to the outer bank. Also, the inception of the scour holes near the inner bank and outer bank was different. However, this difference was decreased during the test progress. [ABSTRACT FROM AUTHOR]

Reservoir sedimentation is significant for the efficiency and life of a dam. Flushing orifices have been used in many small dams and other hydraulic structures to remove deposited sediments. Temporal variations of scour hole dimensions, velocity distribution, and secondary flows in the scour hole upstream of an orifice are investigated here. The experiments were conducted under clear water conditions with three sediment sizes, and three different pressure heads upstream of the orifice. The maximum depth, length, and volume of the scour hole were measured with time. Three flow zones were observed in the scour hole, including inward, outward, and semi-spiral flow zone. Based on regression analysis, some simple equations are presented for the determination of the dimensions of the scour hole. Also, results showed that the maximum scour depth was 10% larger for smaller sizes of the sediments. [ABSTRACT FROM AUTHOR]

Hydraulic model study was conducted on the 1:60 scale using 2-D model for mitigating local scour downstream of ski-jump bucket type energy dissipater under supercritical flow conditions with initial Froude number, Fr1 from 5.50 to 6.29 for all gates vented condition. The objective of this research was to assess and quantify the scour in downstream side of channel and select the most appropriate existing formulas for predicting maximum scour depth of a local scour hole. The relative scour depth for the experimental data is compared with different empirical equations. Among these equations, a good estimate of the measured scour depth is obtained for the Novak and Indian standard equation. The developed statistical equations to predict scour depth give a good agreement with the experimental data. Each scour depth formula has limitations, therefore does not perform well with different discharges for different gate operative conditions. For depth of scour computation, the Novak method is found to provide high accurate results with Nash-Sutcliffe efficiency (NSE) of 0.91, root-mean-square error (RMSE) of 4.66 m and mean absolute percentage error (MAPE) of 15%. However, in a data-constraint situation, the development of a new formula for scour depths computation will be more feasible. [ABSTRACT FROM AUTHOR]

Under a flow in supercritical regime, depending on the pier width to water depth ratio, the flow pattern around a bridge pier can take the form of a wall-jet-like bow wave or a detached hydraulic jump. The present work aims at analysing the maximum scour depth at piers in both flow patterns. A dedicated experimental set-up was used to produce the live-bed scour experiments, varying the inflow velocity and pier diameter. During the experiments, scour developed very rapidly, achieving equilibrium conditions after few minutes. No major differences between the maximum scour depth in the wall-jet-like bow wave and detached hydraulic jump cases were observed. Measured scour depths were of comparable magnitude and followed similar tendencies with controlling parameters as in subcritical flows. Scour formulas for piers in subcritical flow thus achieve a good accuracy in prediction of maximum scour depth at piers in supercritical flows. [ABSTRACT FROM AUTHOR]

This study proposes a scour equation for abutments that is based on a combination of Newton's second law and a turbulence model comprised of a pair of isotropic vortices. A control volume of the scour hole is considered on which the sum of forces equals nil. The effect of abutments on local scour is usually modelled by an empirical K-factor for which there is no physical description available. Here, we deduce a relation between abutment shape and the maximum scour depth by using engineering tools from turbulence science. We pay attention to the scour effects of several types of abutments, such as submerged, non-submerged, permeable and impermeable and the impact of bed protection. We consider the highly nonlinear combination of constriction and local scour. The unknowns in the proposed scour equation are calibrated and validated with several scour tests. [ABSTRACT FROM AUTHOR]

In the present study, experiments were carried out on circular model bridge piers individually as well as with two-piers-in-tandem arrangement under clear water scour conditions predominantly caused by formation of horseshoe vortex. Independent collar plates around bridge piers and a continuous collar plate covering both the piers were installed as countermeasures against scouring. In case of two piers, efficacy of scour-protection devices for front and rear piers was checked for the overall stability. Performance potential was noted to be about 67% and 100% for continuous collar plates of sizes 2.5D and 3.0D around two piers at average bed level with spacing of 2.0D; where D is the diameter of the pier. During degradation of general bed level, a group of three continuous collar plates was employed around both the piers to ensure considerable reduction of scour. A group of three collar plates of sizes 2.5D and 3.0D having an inter-plate spacing Cs equal to D/4 with the middle plate placed at the average bed level reduced scour by 79 and 82%, respectively, in comparison to the scour depth for an unprotected pier. A mathematical model was developed by multivariate regression analysis to prediction the scour depth for both the pier arrangements. [ABSTRACT FROM AUTHOR]

This study was conducted to assess scour problems at three selected bridge sites in the Tigray region, northern Ethiopia, namely the Ilala, upper Geba, and Tankwa bridges. Smart-GIS, ArcGIS, Hydrologic Engineering Centre Hydrologic Modeling System (HEC-HMS), and Hydrologic Engineering Centre River Analysis System (HEC-RAS) were used for the river morphology, hydrologic, and hydraulic analysis. The riverbanks were subjected to higher degradation and instability problems. The estimated 100-year flows were 272.5, 940.4, and 249.9 m3/s for Ilala, upper Geba, and Tankwa bridges, respectively. Flow depth calibration were resulted in model performance with Nash Sutcliffe Efficiencies of 0.90, 0.88, and 0.87 for Ilala, upper Geba, and Tankwa bridge sites, respectively. Scour depths were 1.3, 1.6, and 0.8 m at contracted sections; 3.2, 3.0, and 2.2 m at the piers; 2.6, 3.6, and 2.2 m at the left abutment; and 1.6, 3.0, and 2.1 m at the right abutment of Ilala, upper Geba, and Tankwa bridges, respectively. The use of riprap at the bridges resulted in the reduction of scour depths by 60–100%. Overall, the hydrologic and hydraulic models performed well. [ABSTRACT FROM AUTHOR]

Scour has been recognized as one of the leading causes of bridge collapse in the United States. Therefore, it is essential to be able to build models that accurately capture the response of bridges vulnerable to scour, including those located in layered rather than homogeneous soil deposits. Simple removal of soil springs due to scour ignores the effect of stress history for layered soils, which can lead to unconservative designs of foundations. This article proposes a methodology called the equivalent stress history and layered effects (ESHaLE) approach to capture the impact of soil stress history of layered soils on vulnerability assessment of scoured bridges. It utilises conservation of strength and mass to derive corresponding soil and depth parameters. Results show that neglecting to include stress history impacts in layered soils can lead to an underestimation of the single pile axial displacements by up to 35% in static analysis, and underestimation of the probability of exceeding bridge deck deflection thresholds by up to 25% in seismic fragility assessment. The study presents a method to include both soil stress history and layered effects in soil modeling and shows the importance of including these soil effects in the assessment of bridges vulnerable to scour. [ABSTRACT FROM AUTHOR]

The accurate estimation of scour is essential for the safe design of bridge crossing river. Scour is a complex phenomenon; developing a generalized scour model is a big challenge to the hydraulic community. An artificial intelligence (AI) based Gene Expression Programming (GEP) technique was employed to develop a unique and universal (applicable to laboratory and field conditions) scour model. Model parameters were selected after model-independent sensitivity analysis. The model developed in the present study was compared with the five most widely used empirical scour models. Jain and Fischer model found to have good correlation (0.94 and 0.76 for field and laboratory data, respectively) under classical methods of model development, but an error in the prediction was most (RMSE = 0.06 and 2.08 m for field and laboratory data, respectively) amongst other scour models. The GEP model developed in the present study has good correlation (0.93 and 0.76 for laboratory and field data, respectively) and the least error (RMSE = 0.042 m & 0.78 m for laboratory and field data, respectively) amongst all the models considered in the present study. It is concluded that the AI-based GEP scour model performed better and recommended for its use in the laboratory and the field conditions. [ABSTRACT FROM AUTHOR]

Local scour is an important design factor for submerged weirs. This study conducted a clear-water scour experiment at a submerged weir, using the particle tracking velocimetry technique to measure the flow field in the developing scour hole. The mean flow patterns, turbulence intensities and near-bed Reynolds shear stresses in the scour hole at different scour stages are presented and discussed. The submerged weir alters the mean flow significantly, forming a high-velocity zone above the weir and a vortex system near the scoured bed. As the scour develops, the high turbulence intensity zone and the high near-bed Reynolds shear stress zone both get closer to the upstream slope, and further away from the downstream slope of the scour hole. At the equilibrium stage, although the near-bed Reynolds shear stress near the upstream slope of the scour hole exceeds the critical shear stress of sediment entrainment, sediment moves in a recirculating form such that the scour hole does not further enlarge. [ABSTRACT FROM AUTHOR]

Suction caisson is one of the important forms of marine foundation. It is worthwhile to study scour effects on the vertical bearing capacity of suction caissons, which can provide a reference for the design of multi-caisson foundations. This paper investigated the influence of scour depth, stress history, and aspect ratio on the vertical bearing capacity of suction caissons. The capacity decreases with increasing scour depth, and its scour sensitivity is lower compared with the pull-out response. The capacity after scour is larger when the stress history is considered, so ignoring the stress history leads to a conservative design. The greater the aspect ratio, the greater the scour effect on the capacity. Based on these, an empirical formula for evaluating the vertical bearing capacity of suction caissons after scour is established, which reveals the relationship between the capacity and the scour depth and aspect ratio. [ABSTRACT FROM AUTHOR]

An experimental analysis of the dynamics of avalanches for different stages of development and turbulent flow conditions is introduced. Experiments were conducted in a laboratory flume using clear-water conditions and a video camera placed within an acrylic cylinder. The results of a proper orthogonal decomposition of the pre-processed image sequences highlighted the existence of two types of sand avalanches: Type I corresponding to a narrow and vertically long-advancing slide, and Type II characterized by an elongated and short-advancing pattern. Temporally speaking, sand avalanches were triggered aperiodically, resembling the behaviour of the horseshoe vortex system. The frequency of occurrence of avalanches decreased with time, while the estimated volume of mobilized sand increased in the same period. The sand slide magnitudes and associated inter-avalanche time were Log-Pearson 3 distributed. Sand avalanches are an important scour mechanism, which depending on the flow intensity contribute to about 40% to 60% of the scoured volume. [ABSTRACT FROM AUTHOR]

Computational Fluid Dynamics (CFD) represents a useful tool to study natural currents in the rivers and estuaries with erosive materials; therefore, it is always in the keen interest for scientists to further study and advance it, especially when numerical model has the advantages compared to actual laboratory experiment in terms of cost, time, and restrictions on conditions of the physical models and field collections. The present study deals with the hydro-morphological investigation and numerical modeling of a group of vertically stationed parallel groynes using FLOW-3D commercial software. To validate the results of the FLOW-3D simulation, it has been compared to the experiments from literature. Besides, a SSIIM 2.0 software has also been employed to compare with some of the FLOW-3D results. It was found that the accuracy of the FLOW-3D model influenced by the approach Froude number and the critical velocity ratio (Uavg/Ucr). Even though it underestimated the measured scour depth (due to complex and intense vortices, which reduce the accuracy of the numerical models), but general results from the model have reproduced the measured data well. [ABSTRACT FROM AUTHOR]

The large-diameter monopile, as one of the most used foundations of offshore wind turbines, is subjected to severe sea conditions, such as the cyclic lateral loads induced by wind and waves, as well as the scour induced by the flushing currents. The combined cyclic lateral loads and scour introduces additional complexity and is encountered in offshore wind turbines as well as other offshore structures. In this study, the experimental tests and numerical simulation methods are adopted to investigate the behavior of monopile subjected to the combined cyclic lateral loads and scour. Firstly, the static and one-way cyclic lateral load tests are conducted to investigate the influence of scour conditions and the characteristics of cyclic lateral loads on the lateral displacement and bending moment of monopile. Subsequently, the three-dimensional numerical model is established by employing the stiffness degradation material model, reasonable comparisons between the numerical results and the experimental results suggest that the numerical model can be used as a reliable complement of the model tests. Finally, a series of parametric studies are carried out to investigate the effect of cycle numbers, scour conditions and cyclic load ratio on the accumulated deformation and lateral bearing capacity of monopile. It is found that the accumulated deformations are dependent on the cyclic load characteristics and scour depth, the one-way cyclic load and scour have opposite effects to the lateral capacity of monopile. A framework to predict the accumulated deformation of monopile subjected to the combined scour and long-term cyclic lateral load is developed, which can be served as a basis for the practical design of monopile. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Bridge pier scour is an important issue for safety evaluation of bridges. The existing scour depth prediction equations for bridge piers are mostly deterministic in nature, which do not incorporate the uncertainties due to scour parameters, selection of model and limited information about data. To incorporate these uncertainties, a reliability-based assessment of bridge pier scour is required. An attempt has been made herein to develop a reliability-based scour depth prediction model for live bed scour at bridge piers. An object-oriented constrained optimization technique of the first-order reliability method has been used for the reliability analysis. The influence of uncertainties, type of probability distribution and correlation among the basic input parameters on the failure probability have been studied in detail. To achieve the desired safety level in the design of pier foundation for the live bed scour, the reliability-based safety factor is proposed. A sensitivity analysis has also been carried out to obtain the effect of the individual random variables on the reliability of pier scour. [ABSTRACT FROM AUTHOR]

Empirical equations for predicting local scour depth around bridge piers only consider the effects of hydraulic parameters and do not take into account the uncertainties involved in them. Empirical equations also assume steady-state condition which means the flood peak flows for a long time. In the present study, a methodology is presented for the reliability assessment of bridge piers against scouring considering the uncertainties involved in effective parameters and duration of the flood. Additional necessary experimental studies were also carried out to develop an equation for time development of scouring around a protected pier by a collar. Monte Carlo simulation technique was used for estimating the probability of bridge failure. In addition, Fault Tree analysis was employed for combining the interactions of various parameters and calculating the overall probability of failure. For unprotected piers, results showed that at lower flow intensities, flood time has a lower influence on probability of bridge failure. It was also concluded that the collar protection increases the reliability of bridge piers significantly, especially at lower flow intensities. Furthermore, the model was applied to find a relationship between the reliability index and safety factors under various flow conditions. [ABSTRACT FROM AUTHOR]

Bridges situated close to each other show interference effect on scour depth around bridge elements as compared to the scour depth around isolated bridge elements. A number of investigations have been made in case of a single isolated pier having different shapes and flow conditions. But the investigations on bridges likely to interfere are relatively much lesser. Addressing the issue, an experimental study was conducted with circular and oblong piers of size, D = 6.2 cm forming tandem, side by side and staggered patterns. A recirculating flume 12 m long, 0.6 m wide and 0.7 m high with uniform sized sediment of average size, d50 = 0.23 mm was used for the experimental work. Experiments were run at a velocity equal to 0.93 times the critical velocity, uc. Piers when spaced from each other by a distance of one pier diameter showed maximum scour depths of 1.06, 1.51 and 1.53, respectively, for the tandem, side by side and staggered arrangements as compared to that of a single pier. However, when the inter- pier spacing was 16 times for tandem, two times for side by side and five times for staggered arrangements, the piers behaved independent of each other's presence. [ABSTRACT FROM AUTHOR]

The present laboratory study used particle image velocimetry (PIV) to measure transitional flow regimes during the jet-flipping process, which is cyclical in the scour hole downstream of a sluice gate with an apron. The transitional vortical structures during jet flipping (both upward and downward) are clearly captured and discussed. Various vortices are formed in the scour hole by two pairs of component jets resulting from the impingements of jet on the bed and on the water surface, respectively. Jet-flipping always involves opposite developments of the major vortex and the bed vortex with the two impingement points moving in opposite directions along the bed and the water surface cyclically. Also, the kinetic energy of the issuing jet is dynamically distributed across the vortices which transform interactively in terms of their location, size and magnitude during jet-flipping, as indicated by the distributions of average kinetic energy (AKE) and spanwise vorticity. [ABSTRACT FROM AUTHOR]

The use of complex piers to build bridges has become widespread. In this study the experimental data was obtained to determine scour hole's dimension and its changes versus pile cap elevation. Five models with different geometry were used in experiments under clear water condition and thresholds velocity. The models were made with an appropriate scale from real piers of bridges. A 3D illustration of the model for each experiment was drawn. The length, width and depth of the scour hole coordinates were measured in three directions. The results showed that similar to the scour depth, the scour length and width, apart from pier geometry, are significantly depended on the pile cap elevation. It was found that the variation in scour hole dimensions can be categorized into two cases as before and after pile cap undercutting. Moreover, the maximum length and width of the scour hole at each model were derived. [ABSTRACT FROM AUTHOR]

Multi-temporal repeat monitoring of flood-vulnerable rivers is crucial due to rapid alteration of morphological properties of in-channel landforms. Besides, the characteristics of the river crossing bridges may deteriorate due to flood induced scouring around bridge piles or due to flood loads. Thus, in this study high-resolution topography of the study region was acquired during two consecutive years by unmanned aerial vehicle (UAV) based surveys using Structure-from-Motion (SfM) processing. Following the extraction of digital elevation models (DEM), repeat data that were obtained at each UAV survey were compared using Geomorphic Change Detection (GCD) to calculate volumes of deposition and erosion via DEM of difference (DoD) algorithm. Thus, detailed high-resolution maps of the river channels can be rapidly and efficiently generated by low cost UAV based measurement methods in order for continuous tracking of stream channel morphology for the rivers sensitive to floods. [ABSTRACT FROM AUTHOR]

The scour observed at the landside ground behind coastal protection facilities, such as seawalls and coastal dikes, due to tsunami overflows is the main reason for failures in such constructions. In this study, we focused on sheet-like (two-dimensional) scour countermeasures, which do not require large-scale excavation of the ground, and experimentally verified the effects of geonet and mesh sheets. By applying a vertical jet directly on the ground and increasing the external force, a situation close to the real scale conditions was reproduced. The experimental results show that the geonet material is able to significantly reduce the scour depth on both non-liquefied and liquefied grounds. We show that in the most effective case, the maximum pore-water pressure and the scour depth are reduced by about 91% and 86%, respectively, by the mesh sheet on the sand-bed surface. [ABSTRACT FROM AUTHOR]

In this study, scour-based vibrations of bridge piers are investigated using a bridge model in a water flume. First, the eigenmode corresponding to the measured frequencies of pier-like structures is identified. Second, the effect of the pier–deck interaction is studied. Finally, a theoretical model is proposed to characterize the pier vibration and identify its input parameters. To this end, experiments were conducted and a laboratory-scale model pier was tested in two configurations: single piers and two piers in a bridge configuration. The experimental results enable the identification of the modal shape and indicate that the deck decreases significantly the pier's frequency. In parallel, a theoretical model was proposed to model the pier, where the soil was modeled with both lateral springs along the pier and a rotational spring at the base. The spring stiffnesses were then identified using a three-dimensional finite element model. The results obtained from the theoretical and numerical models are in good agreement with the experimental results with the bridge pier in the two tested configurations. The obtained theoretical, numerical and experimental results were compared to experimental data found in the literature for further validation. [ABSTRACT FROM AUTHOR]

Regulators are commonly used to control and measure flows in streams and irrigation canals. Inadequate operation of regulator gates may lead to scour downstream, possibly leading to structural failure. An experimental work was conducted to study the effect of different regulator gate operation schemes on scour hole formation downstream under free-flow conditions. The experimental model consisted of five sluice gates, a solid apron, and a mobile bed (sand). One hundred and thirty-five different gate operation schemes were studied by changing the number of opened gates and the gate arrangement with different hydraulic conditions. The parameters considered in this study were the downstream Froude number, tail water depth, upstream water head, and the number of opened gates and their arrangements. A dimensional analysis was applied to obtain non-dimensional quantities that describe the different variables affecting scour downstream the gates. The obtained results of the experimental tests were analysed and graphically represented. It was observed that the number of opened gates and their arrangements had significant effects on the scour hole pattern under different hydraulic conditions. The most favourable operation case was with all five open gates opened, while the least favourable operation case was with only the side gate opened. [ABSTRACT FROM AUTHOR]

The scour phenomena around vertical piles in oceans and under waves may influence the structure stability. Therefore, accurately predicting the scour depth is an important task in the design of piles. Empirical approaches often do not provide the required accuracy compared with data mining methods for modeling such complex processes. The main objective of this study is to develop three data-driven methods, locally weighted linear regression (LWLR), support vector machine (SVR), and multivariate linear regression (MLR) to predict the scour depth around vertical piles due to waves in a sand bed. It is the first effort to develop the LWLR to predict scour depth around vertical piles. The models simulate the scour depth mainly based on Shields parameter, pile Reynolds number, grain Reynolds number, Keulegan–Carpenter number, and sediment number. 111 laboratory datasets, derived from several experimental studies, were used for the modeling. The results indicated that the LWLR provided highly accurate predictions of the scour depths around piles (R = 0.939 and RMSE = 0.075). Overall, this study demonstrated that the LWLR can be used as a valuable tool to predict the wave-induced scour around piles. [ABSTRACT FROM AUTHOR]

Coastal finite structures, bridge piers, and bank protection structures may become submerged during storm surges. In the present study, a turbulent flow field around a submerged pile within a scour hole is numerically simulated considering a very fine mesh in the order of 50 million cells distributed within a relatively small computational domain. Necklace vortices, including two horseshoe vortices (HVs) and a junction vortex (JV), are detected upstream from the cylinder. In many snapshots, the tails of the HVs stretch in the flow direction, while their size and length change considerably over time. Downstream of the cylinder, the influence of the trailing vortex from the cylinder roof is mainly limited to a zone near the cylinder top, whereas the effect of the separated shear layers (SSLs) from the cylinder sides is dominant within a larger region. The strength of vorticity associated with the trailing vortex is mainly notable within the "very near wake" area, where the strength of the upward velocity component of the wake vortices generated from the cylinder sides mitigates. This paper describes the distribution and origin of streaks and rollers on the scoured bed, i.e. the main cause of sediment transported downstream of the cylinder. [ABSTRACT FROM AUTHOR]

A simplified method for predicting the nonlinear dynamic response of composite caisson-piles foundation (CCPF) under scour conditions is proposed. The Hardin-Drnevich model is employed to represent the nonlinear soil reactions. Stress history is also considered to study the scour effect on the dynamic impedance of foundation. Then, harmonic vibration tests considering scour are conducted on a CCPF. It can be observed that the predicted trends of the CCPFs response agree with the experimental data, which verifies the reliability of the method. Then, a case study is investigated to evaluate the effects of stress history, scour depth and soil nonlinearity on the dynamic response of the foundation. The results show that soil nonlinearity has a close relationship with the lateral dynamic displacement of foundation, and it will result in a slight reduction in the resonant dimensionless frequency of the CCPFs. Additionally, with increasing scour depth, a remarkable decrease in the dynamic impedances is produced when soil nonlinearity is considered. Compared with soil nonlinearity, stress history is found to have greater influence on the displacement of the CCPFs, especially in the low frequency range. Finally, a discussion is conducted on the relationships between the resonant frequency of the CCPFs and the scour depth. [ABSTRACT FROM AUTHOR]

Sediment has a severe effect on bridge stability, and time-domain reflectometry (TDR) is a suitable method for assessing scour depth. This paper presents a fundamental study to demonstrate the suitability of a circular TDR system to enhance the resolution when monitoring scour depth with consideration of detailed local changes over a wide area around piers. A total of 32 electrodes are vertically installed on a cylinder pier around the circumference at ∼7.36 mm intervals. Scour depth is investigated through small-scale laboratory experiments, where a measured waveform reflects the artificially constructed scour depth with high resolution (≈5 mm). Different scour types including circular, mushroom, elliptical, and irregular shapes are developed to verify the application of circular TDR, and shapes are predicted through the detailed local distribution. The influences of the reflected waveform according to water level change, temperature variation, and salinity effect are investigated as additional considerations, and the relative deviation of scour depth is analyzed. This study demonstrates that the proposed circular TDR system achieves better resolution than existing single TDR systems and may provide a better alternative technique for monitoring scour depth. [ABSTRACT FROM AUTHOR]

Following the Great East Japan Earthquake, a massive tsunami caused serious damage to coastal dikes. Local scour at the ground behind these dikes reportedly causes dike failures. It is important to reveal the scour process to establish methods for effective scour countermeasures. Herein, we focus on geogrids. To verify this proposal and examine its design, flume-model experiments were performed for non-liquefied and liquefied grounds behind coastal dikes. The results showed that the scour amount and area were reduced drastically when geogrids were present. Geogrids on the sand-bed surface changed the direction of overflow water. Thus, a scour hole developed away from a coastal dike model. Furthermore, geogrids exerted a scour-reduction effect even during liquefaction. [ABSTRACT FROM AUTHOR]