Scour Parameters Research Articles

Scours effects on the lateral bearing capacity of monopile-friction wheel composite foundations in sand-overlaying-clay deposit

The monopile-friction wheel composite foundation is recognized as an innovative offshore wind turbines (OWTs) foundation type, distinguished by its superior lateral bearing capacity and resistance to local scouring. In order to investigate the influence of local scour in sand-overlaying-clay deposit on the lateral bearing capacity of this new type of composite foundations, a series of numerical simulations are conducted to explore the effects of potential parameters including different scour parameters, overlying sandy layer thickness and loading point height on the lateral bearing performance. The results indicate that the greatest reduction in lateral bearing capacity of the composite foundation due to scour depth can reach approximately 35%, while the scour extent and angle have relatively small effects. Moreover, the lateral bearing capacity of the composite foundation increases with the thickness of overlying sandy layer. Local scour and the sand layer thickness also affect the lateral deformation and the soil resistance along the pile shaft. Furthermore, as the loading point height increases, the lateral resistance of the composite foundation decreases rapidly. These findings offer valuable insights for the design of monopile-friction wheel composite foundations in sand-overlying-clay deposits.

Baffle-Enhanced Scour Mitigation in Rectangular and Trapezoidal Piano Key Weirs: An Experimental and Machine Learning Investigation

The assessment of scour depth downstream of weirs holds paramount importance in ensuring the structural stability of these hydraulic structures. This study presents groundbreaking experimental investigations highlighting the innovative use of baffles to enhance energy dissipation and mitigate scour in the downstream beds of rectangular piano key weirs (RPKWs) and trapezoidal piano key weirs (TPKWs). By leveraging three state-of-the-art supervised machine learning algorithms—multi-layer perceptron (MLP), extreme gradient boosting (XGBoost), and support vector regression (SVR)—to estimate scour hole parameters, this research showcases significant advancements in predictive modeling for scour analysis. Experimental results reveal that the incorporation of baffles leads to a remarkable 18–22% increase in energy dissipation and an 11–14% reduction in scour depth for both RPKWs and TPKWs. Specifically, introducing baffles in RPKWs resulted in a noteworthy 26.7% reduction in scour hole area and a 30.3% decrease in scour volume compared to RPKWs without baffles. Moreover, novel empirical equations were developed to estimate scour parameters, achieving impressive performance metrics with an average R2 = 0.951, RMSE = 0.145, and MRPE = 4.429%. The MLP models demonstrate superior performance in predicting maximum scour depth across all scenarios with an average R2 = 0.988, RMSE = 0.035, and MRPE = 1.036%. However, the predictive capabilities varied when estimating weir toe scour depth under diverse circumstances, with the XGBoost model proving more accurate in scenarios involving baffled TPKWs with R2 = 0.965, RMSE = 0.048, and MRPE = 2.798% than the MLP and SVR models. This research underscores the significant role of baffles in minimizing scouring effects in TPKWs compared to RPKWs, showcasing the potential for improved design and efficiency in water-management systems.

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

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

Bed configurations downstream combined V-Notch-sharped edged Weir with inverted V-Shaped gate

ABSTRACT 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.

Effects of local scouring on capacities of monopile-wheel composite foundations in sand under lateral loading

This paper focuses on an innovative foundation type of monopile-friction wheel composite foundations, which aim to enhance the loading performance of offshore wind turbines (OWTs) while mitigating the negative impact of local scouring. The study utilizes numerical simulations to investigate the morphology of local scouring under unidirectional flow. Furthermore, the finite element method is employed to quantify the lateral bearing behavior, considering different scouring parameters, loading point heights, and pre-torsional loads. On this basis, the load bearing ratio of each part of the composite foundation under different scour conditions is also obtained. The results reveal that the horizontal bearing characteristics are significantly influenced by different scour parameters, loading point heights and pre-torsional loads. The local scouring can reduce the bearing capacity by about 38%, with scouring depth having the greatest effect, followed by the scouring angle and extent respectively. Moreover, as the loading point height and pre-torsional load increase, the lateral bearing behavior of composite foundations decreases. Notably, the friction wheel contributes more than 40% to the overall bearing capacity, underscoring its importance. The results provide valuable insights into further understanding the bearing behavior of the composite foundation and its potential engineering applications.

Effects of Secondary Current on the Local Erosion Induced by Circular Turbulent Wall Jets in Cross Flow

This paper presents the results of a series of laboratory experiments, by placing a turbulent wall jet in the upstream and downstream of a 90° channel bend, to investigate the effects of secondary flow on formation of local sediment erosion and deposition. The effects of jet and current flow intensities on the erosion pattern were characterized by the jet’s Reynolds number, Re, channel Froude number, Fr, and the ratio of water depth to nozzle diameter, h/do. The geometrical characteristics of local erosion such as jet trajectory, maximum scour depth, ds, and maximum mound height, hm, were measured. The area and volume of scours and mounds were calculated from measurements, and the results were correlated with the controlling parameters. Experimental observations indicated the existence of distinct scour patterns due to variations of channel Froude number. Two additional scour holes were identified due to the effect of stream interactions and formation of vortex regions immediately downstream of sediment mound. It was found that both channel and jet flows contributed to trajectory of the jet and the footprint of erosion. A threshold Froude number of Fr=0.091 was identified at which the current and jet flow were in equilibrium. The results showed that for a constant value of Fr, all scour parameters increased with increasing Reynolds number. However, Re did not have any effects on the jet’s deflection. Comparing the erosion profiles in the upstream and downstream bend indicated that the secondary current and turbulent redistribution altered the erosion and mound formation in the downstream of the bend in relatively high Reynolds (i.e., Re≥23,000), high channel Froude numbers (i.e., Fr>0.091) and high jet submergence (i.e., h/do>10.53).

Temporal evolution of scouring downstream of a trapezoidal piano key weir

ABSTRACT This study experimentally investigated the temporal evolution of the scour parameters downstream of a trapezoidal piano key weir. The densimetric Froude number (Fr d50) in the range of 0.39–0.57 and the relative vertical distance of the sediment bed level to the weir toe (Δz/P) in the range of 0.025–0.5 were taken into consideration. In general, with an increase in Fr d50, the scouring rate, maximum scour depth, scour hole area and scour hole volume enhanced over time. The increases in the scour parameters were greater at the initial stages of the tests. About 87, 80, 65 and 70% of the maximum scour depth, weir toe scour, scour hole area and scour hole volume occurred within the first 20% of the durations of the tests, respectively. Any increase in Fr d50 and Δz/P augmented the scour depth at the weir toe. The results also indicated that the distance of maximum scour depth from the weir increased for greater values of Δz/P and Fr d50. The amounts of scour downstream of the outlet keys were greater than those downstream of the inlet keys. The trend of variations of the longitudinal bed profiles remained nearly unchanged over time. New equations were developed to predict the temporal variations of scour parameters, with acceptable accuracy.

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

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

Scour morphology downstream of submerged block ramps

In this study, the effects of geometric parameters, such as the ramp roughness size and the ramp slope on the scour parameters downstream of block ramps, are experimentally investigated for different hydraulic conditions. Scour parameters, such as the maximum scour depth and length and the maximum ridge height and length, are evaluated. Experiments are conducted in clear water conditions (no sediment transport) for different gravel ramp slopes in which different critical flow depths and tailwater depths are examined. The results indicate that the maximum scour depth downstream of a block ramp for different bottom slopes is directly affected by the tailwater depth, independent of the critical flow depth; the scour depth decreases by increasing tailwater depth. A comparison of the results indicates that increasing the roughness of the block ramp leads to a reduction in the maximum scour depth.

Effect The Shape of Stilling Basin on Scour Downstream Heading-up Structures.(Dept.C)

The objective of this research is to investigate how the shape of stilling basin affects the flow and the principal dimension of local scour downstream heading up Structures. Twenty-sixth type shapes of stilling basin have been designed in conjunction with weirs. Seventy-two runs were conducted considering various stilling basin shape with different flow conditions. Relationship between the shape of the stilling basin, slow conditions and scour parameters were developed from the data obtained from experimental tests.

Hydraulic Modelling of Riverbed Embankment Under the Hričov Weir

The weir of the Hričov water structure has an untypical shortened stilling basin, which affects significant scour development in the downstream riverbed. A rockfill embankment structure adjacent to the stilling basin was constructed to prevent the formation of scours in the riverbed. However, increased flows at the weir erode this fortification and it is necessary to replenish the material back to the embankment after the flow situations. A 2D hydraulic model constructed in a flume of the Hydraulic laboratory was used for the research of new downstream fortification, which would be better resist the scouring effects. The model was created according to Froude’s modelling similarity as a 2D model of the weir structure with control gates and part the downstream riverbed consisting of gravel. Different designs of the embankment were not allowed to interfere with the existing construction of the water structure. The construction of the embankment was designed as a concrete “secondary” stilling basin adjacent to the existing one. Tested variants of the embankment were of different length and depth of the stilling basin. The length varied from 11 to 24 m and the depths varied from 0 to 1,8 m. Overall 11 different design of the embankment were investigated. Each design was tested for three different flow rates on the model simulating common and extreme flow situations at the weir. The flows were selected to simulate also different hydraulic phenomena at the weir – overflow, outflow, and free overflow. After each flow simulation the scour in the riverbed was measured. The measured scour parameters were depth of the scour, the distance of the deepest point from the existing water structure and the amount of the material carried away. The resulting parameters were assessed with respect to each other for the corresponding flow rates. The best results in scour reduction were achieved for horizontal embankment with the depth of 0 m. The designs with increased depth were causing secondary hydraulic jump in the riverbed which increased the scours. The tested designs of the embankments were able to reduce scour size by up to 45% for the outflow, by less than 20% for free overflow and by more than 80% at the overflow.

Hydraulics and bridges: A French case study of monitoring of a bridge affected by scour

Bridges are one of the oldest types of civil engineering structures and the interaction between the transport and hydrographic networks represents a significant issue in a country such as France. Recently, various cases highlight the importance and vulnerability of civil transport works in relation to their environmental hazards, e.g. floods, and therefore the need to develop integrated observation tools and warning systems in the aim both of optimizing the management system and of increasing the knowledge on real scour processes. This paper reports on the “field approach” task of a research project aiming at improving continuous monitoring in order to follow the evolution of the scour processes of a given bridge or abutment. The first step has been to identify a pilot site, representative of scour vulnerability. After a report of the scour parameters to be monitored, the benchmark study and the choice of monitoring devices available on the market are detailed. Instrumentation, sensor adaptability, limitations (actual measurement ranges, ergonomics, energy supply limits …) and in situ implementation are then presented and discussed. Finally, preliminary measurements, post-treatments and interpretation are detailed.

Prediction of scour downstream of triangular labyrinth weirs

Estimation and control of local scouring downstream hydraulic structures is an important aspect for designing hydraulic structures. Lack predicting of local scouring can cause endangered hydraulic structures. This study performed aseries of laboratory experiments in order to look for the scouring at the downstream of triangular labyrinth weir. The effects of four different weir apex angles on the local scour were tested. The tested angles were 90°, 75°, 60°, and 45° under varied rates of flow. A wier of linear crest ‘180°’ was also included in the test program to distinguish the rendition of the triangular labyrinth weir and to benchmark some existing formulas of local scouring downstream weirs. Consequently, a great reduction of the scour parameters was obtained. Results referred to that the best weir apex angle was found to be 60°, which produced minimum values of scour parameters downstream the triangular labyrinth weir. The formulas of others performed well compared to experimental results. Moreover linear regression formulae were also proposed.

The Science behind Scour at Bridge Foundations: A Review

Foundation scour is among the main causes of bridge collapse worldwide, resulting in significant direct and indirect losses. A vast amount of research has been carried out during the last decades on the physics and modelling of this phenomenon. The purpose of this paper is, therefore, to provide an up-to-date, comprehensive, and holistic literature review of the problem of scour at bridge foundations, with a focus on the following topics: (i) sediment particle motion; (ii) physical modelling and controlling dimensionless scour parameters; (iii) scour estimates encompassing empirical models, numerical frameworks, data-driven methods, and non-deterministic approaches; (iv) bridge scour monitoring including successful examples of case studies; (v) current approach for assessment and design of bridges against scour; and, (vi) research needs and future avenues.

A reliability-based assessment of live bed scour at bridge piers

ABSTRACT 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.

Impact of Upstream Bridge Pier on the Scouring Around Adjacent Downstream Bridge Pier

The study aspires to investigate a relative scour condition around three-pier group. It identifies the upstream downstream scour geometries when two tandem piers are placed inline and third pier is placed eccentrically in middle of tandem piers. Laboratory scale experiments were physically performed by gradually varying the intermediate longitudinal spacing in between tandem piers. After each experimental run, the scour formation around the pier group and the dune formation downstream of the pier group are investigated. The main aim here is to experimentally identify and highlight the nature and location of scour formed around and also to identify the location of the dune formed downstream of this pier group due to combined interference of flow. The spacing between the inline piers were varied to identify which relative spacing produces the maximum scour. A detailed investigation shows significant effect of inline pier spacing on scour parameters. It was observed that for such three pier combinations, the scour so formed near staggered piers was found maximum and around tandem downstream pier was found minimum. It confirms the shifting of sediment load away from this pier group and is deposited downstream, drifting more towards the staggered pier that is towards channel sidewall. Equations are proposed with respect to the pier spacing between tandem piers to evaluate the scour depth around individual pier of the pier group combination.

PREDICTION OF SCOUR AROUND HYDRAULIC STRUCTURE USING SOFT COMPUTING TECHNIQUES

The problem of accurate prediction of the depth of scour around hydraulic structure (trajectory spillways) has been based on the experimental studies and the equations developed were mainly empirical in nature. This paper evaluates the performance of the soft computing techiques, Adaptive Neuro-Fuzzy System (ANFIS), for the prediction of scour around hydraulic structure. The results are very promising (AE = -0.09882 %, = 12.509 % and RMSE = 0.56921) and demonstrate the strength of these intelligent techniques in predicting highly nonlinear scour parameters.

Simulative modeling of the soil erosion processes

Abstract In order to visualize the negative consequences of soil erosion processes running in Georgia, namely in the Gldaniskhevi ravine within the territory of Tbilisi, research field integrated polygon has been arranged on the eroded slope chosen beforehand. At the control area of polygon 24 field experiments have been carried out to study the dynamics of the formed erosion processes under the different intensity precipitation conditions, whereby scour parameters were being measured (average depth – h, average width – b, B). For estimating the exactness of calculations done on the results of measurings accomplished with the purpose to definite the intensity of soil erosion processes, the method of least squares have been used, on the base of which contour dependence between investigated parameters and therefore validity of the accomplished researches have been ascertained. Simulative modeling of the soil erosion processes has been accomplished by means of special computer programs, which has shown, that during 167 days at the control area of the field polygon the eroded slope gulleying processes have been significantly strengthened, that nowadays can be also noticed on the slopes outside the polygon, on account of which can be concluded, that in order, to prevent expected landslide and debris flow phenomena in the river Gldaniskhevi ravine, implementation of urgent effective anti-erosive measures is needed.

Comparing the Scour Upstream of Circular and Square Orifices

Scour pattern upstream of square and circular orifices with equal opening areas of 38.45 cm2 are compared experimentally. A total of 16 tests for four constant heads, two initial conditions of fixed bed versus mobile bed and two non-cohesive sediments used as the bed layer are performed. The bed profile is surveyed by an acoustic bed profiler and the velocity distribution is measured using an ADV instrument. In the fixed-bed tests the thickness of sediment layer below the orifices’ invert is 2 mm and the observations show that the influence zone, which is the zone exposed to excess shear stress in which particles are removed, is elliptically shaped in both orifices with larger ellipse radius in transverse direction. The influence zone area upstream of square orifice is 1.46 times larger than the circular orifice. Observations of the mobile-bed tests indicate that the geometrical scour parameters, namely maximum depth of scour, length and width of the scour hole increase with the head of water upstream of both orifices. It is also found that the maximum scour depth upstream of square orifice is approximately two times deeper than that of circular orifice. Meanwhile, scour length and width, upstream of square orifice are, respectively, 10–15 and 20–33% larger than those of circular orifice. Finally, the measurements of the longitudinal velocity profiles along the centrelines of the orifices for both orifices are performed. The results indicate the existence of three separate zones of velocity distribution upstream of the orifices.

Granular Computing for Prediction of Scour Below Spillways

Effective estimation of scour parameters downstream ski-jump buckets is very important for risk management plan. This paper presents a new method for prediction of the depth, length, and width of the scour hole downstream ski-jump buckets based on granular computing (GrC) technique. This method employs various independent hydraulic, morphologic, and geotechnical factors to predict dependent scour parameters. Evaluation of the results indicated that the dependent scour parameters are affected more by the discharge, falling height, and mean sediment size and less by the lip angle of the bucket. Analyses of the obtained results demonstrated the high accuracy of the GrC, as the predicted values were in good agreement with the observations. Furthermore, statistical equations were derived based on the multiple linear regressions (MLR) to model the relationship between the scour parameters. Despite our expectations, the results of MLR, as a simple model, were excellent as compared to GrC. MLR results were also superior to those of well-known empirical equations presented to date. The GrC gives the best performance for the prediction of scour parameters; however, MLR model is also suggested for any real cases because it can be more applicable by practical engineers than GrC as a black box model.