Scour Hole Dimensions Research Articles

Investigation of dredging pattern due to changes in jet cross-section

Sediment management is a significant part of the decision-making process that hydraulic engineers need to undertake as it has a direct bearing on the environment. Sediment dredging from around intake structures and reservoirs impose a high operating cost. Jets can efficiently remove large quantities of sediment at low operational costs. This study assesses the scouring pattern development by changing nozzle parameters to achieve maximum scouring conditions. Toward this end, scour holes induced by jets generated using the nozzles with four inner angles (30°, 45°, 60°, and 90°) are tested on a cohesionless sediment bed. The experimental results show that the inner nozzle angle, α, and the densimetric Froude number, F0, affect the scour pattern. This work illustrates that the scour hole dimensions grow with increasing α and F0. Based on the velocity measurements, for the range of jet discharges considered herein, the relative velocity Um/ U0 is increased by 20%–25% for the nozzle with α = 90° compared to the nozzle with α = 30°.

Effect of rasp heads with an equivalent height of end sill on scour hole dimensions downstream weirs

Effect of rasp heads with an equivalent height of end sill on scour hole dimensions downstream weirs

Reducing Scour Hole Dimensions around Bridge Circular Piers Using Hexagonal Collars

Reducing Scour Hole Dimensions around Bridge Circular Piers Using Hexagonal Collars

Scoured failure wedge model for analysis of scoured pile-soil interaction in sand

Comprehensive assessment of scour effects is an important consideration in the design of pile foundations in water bodies because they can have a significant impact on the performance and bearing capacity of piles and the integrity of the supported structure. This study presents a scoured failure wedge (SFW) model to simulate the interaction between the laterally loaded pile and sand with local scouring. The developed model is incorporated into an efficient theoretical method to analyze the nonlinear behavior of laterally loaded piles under scour conditions accounting for the scour-hole dimensions and soil stress history. The developed SFW model is validated by comparing its predictions with experimental observations from relevant literature. Subsequently, the validated solutions are utilized to investigate the lateral performance characteristics of the pile under scour conditions. The findings reveal several important insights: (1) the impact of scour on soil properties is primarily confined to the shallow zone, approximately four times the scour depth (4 Hs) below the mudline after scouring; (2) the scour hole dimension has a more pronounced influence on the behavior of laterally loaded piles compared to the soil stress history; and (3) the pile response under lateral loading is positively related to the depth and width of the scour hole and negatively related to the slope angle of the scour hole.

Effect of wave motion on the scouring caused by a marine propeller jet: An experimental and numerical study

Bathymetry changes induced by marine propeller jets on movable beds are a crucial issue in harbors, especially in the maneuvering zone. The knowledge of the scour hole and deposition mound dimensions, due to propeller jets, is important in the context of sediment management.Although the presence of waves is well known in harbor environments, propeller jet scours are usually investigated under still water conditions neglecting the effect of wave interaction. Moreover, the interaction between waves and propeller jets can also occur in mooring out of harbors. For these cases, the interaction of wave induced hydrodynamics and propeller jets is a crucial issue that is still an open and challenging problem. This paper aims to address, for the first time, the knowledge gap by investigating the influence of waves on propeller jets in unconfined conditions, which in turn can lead to alterations in scour and deposition patterns. The study relies on a specific experimental investigation. The selection of the parameters of the experimental tests is based on the results of prior analyses aimed to investigate the propeller jets induced scour and deposition in still water conditions and in the presence of a current. Hence, regular waves with different parameters (i.e. wave height and wave period) have been then reproduced in a wave flume where a propeller jet has been installed. The experimental tests aimed to get insight on the scour profiles as well as scour hole bathymetry induced by propeller jets under the influence of regular wave propagation. Numerical simulations have been also performed to investigate the effects of the wave-induced velocity acting on the propeller jets hydrodynamics. Spectral analysis has been then applied to characterize the complex scoured form and bedforms on the bathymetry configuration induced by the tested propeller jet and waves.

Influence of collar's shape on scour hole geometry at circular pier

Bridge collapses, which are frequently caused by scouring or other hydraulic complexities, have disastrous socioeconomically consequences. Accordingly, this paper offers clear water scour experimental investigation that assesses the impacts of circular and novel hexagonal collar shapes on scouring around circular piers which embedded in a uniform sand bed. Scour geometry was analyzed for both protected and unprotected piers, along with evaluating the percentage reductions of the scour hole dimensions and volume. The results demonstrate that the suggested collars have a considerable effect on separation, stagnation, and dissipation of the impinging downflow and vortices, resulting in a substantial impact on the scour geometry and significantly mitigates local scour. In conjunction with the laboratory data, empirical predicting formulas for scour dimensions and novel coefficients for the effect of collar shape are proposed. To incorporate a novel consideration of estimating scour depth at collared piers, the common prediction equations were updated by adding the newly developed collar shape coefficient. The proposed and upgraded formulas are compared and validated, and the findings demonstrate robust consistency.

Effect of geometry and hydraulic parameters on the bed morphology in a confluence using numerical approach

The confluence of rivers is an important phenomenon that is really vital for irrigation and water transmission networks. Investigation on bed morphology at the junction of two streams is of great importance. Flow complexity at confluences, as well as being at risks of rising water levels and flooding, interfering with the use of bridges, filling the inlets of the ponds and reducing the efficiency of water transport are resulted by this phenomenon. The purpose of this research is to investigate the effect of geometric and hydraulic parameters, such as junction angle, width ratio of two intersected canals, and Froude number on the bed morphology at intersection, using SSIIM2. Validation of the results of numerical model in terms of hydraulic and morphology parameters indicated good correlations coefficients of 0.9 and 0.68, respectively. In the next step, the effect of intersection angle (45, 60, 75, 90 and 105 degrees) on the scour depth was investigated. By decreasing the junction angle from 105° to 45°, the maximum scour depth reduced to about 96% and the scour hole dimensions were smaller and moved toward the confluence shore. Furthermore, the results showed that by increasing the width ratio from 0.5 to 1, and also, decreasing the Froude number ratio of tributary to main channel from 3 to 0.68, maximum scour depth decreased by 25% and 30%, respectively.

Seismic analysis of a monopile-supported offshore wind turbine considering the effect of scour-hole dimensions: Insights from centrifuge testing and numerical modelling

Monopile-supported offshore wind turbines (OWTs) deployed in seismic-active regions are inevitably threatened by the combined effect of earthquake and scour. However, current codes and research fail to adequately address the seismic response of OWTs under different scour conditions. In this study, a series of centrifuge shaking table tests were conducted on a monopile-supported OWT model subjected to both local scour and general scour. The test results show that the amplification effect of general scour site is more pronounced than that of local scour site. Moreover, the maximum bending moment from the general scour cases are mostly larger than those from the local scour cases under relatively large scour depth. This indicates the possibility of an over-conservative design when simply reducing the local scour condition to general scour condition. Then, based on the centrifuge tests, a practical 2D finite element model is proposed, in which not only the inertial and kinematic effects but also the effect of scour-hole dimensions on the ground motion input pattern and the vertical effective stress along the pile are incorporated. Further parametric study shows that the kinematic effect plays a significant role in the pile response and cannot be simply neglected even under scoured conditions.

Influence on the lateral response of offshore pile foundations of an asymmetric heart-shaped scour hole

The presence of local scour seriously jeopardizes the safe operation of offshore wind power systems, as local scour leads to the formation of scour holes, which will decrease the bearing capacity of the foundations of these structures. Due to the directionality of waves and currents, scour holes typically have an asymmetric plane shape that creates unequal soil pressure on each side of the pile, and this pressure difference will have a more unfavorable impact on the pile lateral response than that of a scour hole with a symmetric geometry. In this study, an asymmetric heart-shaped scour hole is defined, and parametric analyses are performed to determine the pile lateral response using a three-dimensional (3D) finite element (FE) method in which the scour hole dimensions and the loading directions were varied. As the scour depth increased from 1.0D to 5.0D, the difference in the reduction ratio between the pile lateral capacities for the two scour hole shapes increased from 0.2% to 7.0%, while the gap in the pile bending moments decreased. Moreover, the results indicated that a heart-shaped scour hole was not sensitive to changes in the side slope angle. The pile lateral capacity was found to be lowest when the lateral load was applied negatively along the y axis; the gap in the pile maximum bending moments for the three loading directions was 90 kN·m, and the gap reduced as the scour depth increased.

Experimental study of scour characteristics and scour hole dimensions in consolidated silt sediment under a current

Field observations show that silt is not always loose and that silt consolidation is common. In the study reported here, the characteristics of pile scour in consolidated silt (CS) under clear-water conditions were investigated and compared with those in loose silt. Experiments were performed to study the dimensions of equilibrium scour holes in CS, and the results show that the scour depth and radius in CS are smaller than those in loose silt, but the slope angle in CS is larger and the scour depth is inversely proportional to the dry density. It is found that the scour characteristics in CS differ from those in commonly used fine sand and silt, and most of the existing scour equations cannot predict the scour depth in CS. A mathematical relationship between the scour hole dimensions and the maximum scour depth applicable to CS is established, and a new equation is proposed for computing the maximum scour depth in CS with an error of less than 25%. The present work offers theoretical guidance for the design of scour prevention of piles and scour hole repair in CS.

Unconfined propeller scour in waterways: The role of flow intensity

Flow intensity represents an important input to be investigated in the ship propeller jet scouring process in ship maneuvering areas, waterways path, and mooring in navigation channels. Although the still water condition is not realistic, since it induces modifications in the canonical propeller jet scouring process in waterways, several studies were based on this assumption and only a few papers focused on the influence of the flow intensity are present in the technical literature. In this work, an experimental campaign aimed at exploring the flow intensity effects on the propeller jet and related scour was carried out. In particular, three flow intensities combined with different propeller submergence depths were tested. The experimental results are shown in terms of longitudinal and cross-sectional scoured bed profiles, and empirical equations to compute the main scour hole dimensions are proposed. Moreover, scour hole bathymetries were analyzed by spectral analysis to estimate characteristics length scales. In order to increase the detail on the fluid mechanics analysis to explain the influence of the flow intensity on the evolution of the scour hole and obtain an insight into the influence of the boundary effect on the flow field, Reynolds-Averaged Navier–Stokes simulations were performed over the three-dimensional scoured bathymetry, acquired at the equilibrium stage, and over the horizontal boundary, representing the earliest stages of the scouring process. The good agreement between the numerical results and the measured velocities at the equilibrium stage allowed also the simulations over a flat bed in the same hydraulic conditions. These represent the beginning of the scour process in the case in which the propeller blades are close to the bottom. As to the authors' knowledge, the last configurations were never simulated before, owing to the difficulties in managing the computation of a moving mesh close to a solid boundary. The results show, for the first time numerically, the plane boundary effects on the characteristics of propeller jets with and without an incoming flow.

Relationship between eroded volume and main scour hole dimensions near quay walls caused by internal counter-rotating twin-propellers

The present study aims at computing and analysing the eroded sediment volumes induced by twin-propeller jets near a vertical quay wall from the main geometric characteristics of the scour hole. Two different scouring mechanisms govern the scouring process: i) the down-flow due to the interaction between the propellers jet and the wall, and ii) the direct impact of the propellers jet flow on the seabed. For this reason, the whole study area is divided into two subzones: 1) 'near the wall' field; 2) 'far from the wall' field. Both forward and backward rotation of the propellers during manoeuvring are analysed. The results show that, for the two manoeuvring states, the relationship between the eroded volume and the geometric characteristics of the scour hole in the near-wall subzone does not change, meaning that the backward rotation does not affect the morphology of the scour hole near the wall. Moreover, the eroded volume can be determined as a function of the maximum depth near the wall and, with higher accuracy, as a product of the three main geometric characteristics of the scour hole at any time-stage during the scour hole development.

Scour effects on lateral responses of pile groups in clays

In contrast to single piles, pile groups experience more capacity loss by scour due to not only geotechnical group effect but also hydraulic group effect. However, existing standards only include design considerations for scoured single piles, and scour effects on lateral responses of pile groups are not fully appreciated. This study proposes a practical method to analyze lateral responses of pile groups in soft clays affected by local scour. The proposed method was verified against the results of 3D continuum finite element (FE) models, in which the baseline no-scour 3D FE model was established based on a reported full-scale load test. Parametric analyses were conducted to investigate the effects of scour-hole dimensions and pile group configurations on the lateral responses of pile groups in soft clays. The suitability of applying the methods specified in the various standards for a scoured single isolated pile to a scoured pile group was assessed by comparing them with the proposed method and 3D FE analyses. The results also highlighted the importance of the hydraulic group effect in the evaluation of lateral behavior of scoured pile groups. This research recommends a rectangular pile group shape with greater pile spacing in the foundation design against scour.

Combined Effects of Soil Stress History and Scour Hole Dimensions on Laterally and Axially Loaded Piles in Sand and Clay under Scour Conditions

Removal of soil around a bridge foundation due to scour results in a reduction of the lateral and vertical foundation capacity due to the loss of soil support. The common approach in modeling the scour phenomenon of removal of soil springs without modifying the parameters of the remaining soil fails to consider the change of stress state of the remaining soil and the formation of scour hole geometry around the pile foundation. In practice, both of these factors impact the mechanical properties of the remaining soil and the resulting expected structural response of the pile under loadings. This paper proposed a methodology to comprehensively evaluate the combined effects of stress history and scour hole dimensions on piles under scour conditions in uniform soil. It enabled the examination of the lateral and axial behaviors of a loaded pile subject to scour and is applicable for both cohesive and cohesionless soils. The methodology was validated with results from field tests for no-scour scenarios and verified with existing numerical models for scour scenarios. Quantification of the soil effects was investigated through lateral pile deflection and load-settlement curves for lateral and axial behaviors, respectively. Load-settlement curves demonstrated that including the effect of stress history results in increases of up to 34.1% and 61.1% in estimated pile settlement for sand and clay, respectively, leading to potential unconservative designs if soil effects are not properly included in the analysis.

Equilibrium scour hole size at setback abutments with varied aspect ratios in floodplains

The key features of the equilibrium scour depth dse, width Wse, length Lse and the volume Vse with large abutment aspect ratios (i.e., abutment width Lc divided by its length L) in floodplain are different compared to narrow abutments. Seven models with Lc/L ranging from 0.125 (narrow abutment) to 4 (very wide abutment) were tested. The results show that the combined effect in terms of the abutment aspect ratio Lc/L is a key parameter with wide abutments. Furthermore, the average equilibrium scour width observed was much larger than previous studies and extends up to 3.5 times the floodplain water depth. This implies the current guideline by FHWA (Federal Highway Administration), (2009) to provide a riprap countermeasure apron width for 2 times the floodplain water depth may be insufficient. The much wider scour formation is caused by the migration of the maximum scour location around wide abutments. The results show generally the scour hole dimensions for setback abutments in compound channel are less than that abutments in rectangular channel under the same flow conditions. To this end, empirical equations, which agree well with the data from the present and previous studies are proposed to predict these characteristics at the equilibrium state.

Lateral responses of monopile-supported offshore wind turbines in sands under combined effects of scour and earthquakes

Offshore wind turbines (OWTs) supported by monopiles can be vulnerable to scour and liquefaction triggered by waves and earthquakes. However, the combined effects of scour and earthquakes on the monopile-supported OWTs in sands are not fully appreciated. This study proposes a practical method to evaluate the post-scour seismic responses of piles in sands and applies it to analyze the monopile-supported OWTs. This method introduces a new concept that relates scour-hole geometric conditions to soil liquefaction potential. Using the proposed method, a parametric study was conducted to evaluate the effects of scour-hole dimensions, sand relative densities, and input ground motions on the lateral responses of OWTs. The results showed that scour shifted the fundamental frequency of the OWT system into the rotor frequency range, causing resonance. An increase in scour depth increased the dynamic responses of the monopile and tower, which was less significant in liquefied than in non-liquefied condition. • A practical method is proposed to simulate dynamic soil-pile interactions in sands under scoured conditions. • Computer scripts are developed to analyze post-scour seismic responses of monopile-supported offshore wind turbines (OWTs). • A parametric study was conducted in time domain to investigate lateral responses of a selected monopile-supported OWT. • Contributions of inertial and kinematic interactions to dynamic responses of OWT were assessed by cross-correlation analyses. • The scour effect on the dynamic responses of OWT was more remarkable in the non-liquefied case than in the liquefied case.

Effect of synthetic fibers on resisting scour caused by horizontal jet

Given that the development of scour downstream of hydraulic structures increases the risk of structural damage, it is important to find cost-effective and environmental approaches to reduce this risk. This study aimed to experimentally evaluate the effect of synthetic fibers on the scour profile downstream of a sluice gate with a rigid apron. Experiments were performed with the same Froude number and with different weight percentages of synthetic fibers on both non-cohesive and cohesive sediments. One uniform sand was used as the non-cohesive sediment, and three different cohesive sediments were prepared by mixing different percentages of kaolinite soil with the used sand. The scouring experiments showed that the presence of synthetic fibers did not considerably affect the scour hole dimension in non-cohesive sediments. Evaluation of the scour in the cohesive sediments in silty sand (SM) texture found that an increase in the percentage of silt reduced the scour hole dimensions. The effect of synthetic fibers on scour of SM-texture-based sediments was also investigated, and the results showed that increasing the percentage of synthetic fibers decreased the scour hole dimensions. In addition, the cohesive sediments in SM texture did not have a similar non-dimensional scour profile, and the presence of synthetic fibers did not significantly affect the scour hole.

Prediction of temporal variation of scour hole dimensions due to plane wall jets: Application of new soft computing techniques

Scour due to wall jet is one of the important problems in hydraulic engineering field. Prediction of the scour hole dimensions with acceptable accuracy is necessary for the structures around the jets. In this issue, use of soft computing (SC) methods is unavoidable due to the complex process of jet scour. In this research, SC techniques such as random forests (RF), particle swarm optimization based fuzzy inference system (PSOFIS), slime mould algorithm based fuzzy inference system (SMAFIS) and adaptive neuro fuzzy inference system (ANFIS) were implemented for predicting temporal variation of the scour hole dimensions due to plane wall jets for the first time. The performance indices and the data distribution showed that among the above-mentioned methods, the RF could predict the scour hole dimensions with the highest accuracy. This is attributed to this fact that RF which is a substantial modification of Bootstrap averaging, increases the precision of estimated prediction by a collection of de-correlated regression trees. The hybrid methods, PSOFIS, SMAFIS and ANFIS were ranked from the best to the worst based on the performance indices of the test data. The sensitivity analysis showed that among the effective parameters, the scouring time and sediment standard deviation had the most and the least effects on the temporal variation of scour hole dimensions, respectively. Use of channel width ratio and jet Reynolds number along with other effective parameters such as densimetric Froude number, tailwater depth ratio, sediment size ratio in the models are recommended to reach appropriate accuracies. Comparison with the existing literature indicated that the accuracy of the proposed methods is considerably better than the previous researches.

Investigation of Local Scour Hole Dimensions around Circular Bridge Piers under Steady State Conditions

The local scour around bridge piers is one of the main causes of bridge failures. In this study, scour hole dimensions around circular bridge piers were investigated under clear water scour conditions for various steady flow rates. The experiments were performed with four different bridge pier diameters and seven different flow rates by using uniform sediment with a median diameter of 1.63 mm and geometric standard deviation of 1.3. After each experiments the bathymetry of scour hole was determined. New empirical equations to estimate scour hole length, scour hole width and scour hole volume (V) are proposed by using experimental findings and experimental data available in the literature. The experimental results were also compared with those calculated using several empirical equations given by previous studies. Since there is a lack of data about scour hole dimensions, the experimental findings presented in this study are useful for the researchers investigating the local scour process, and have contributed to the few experimental data in the literature.

Effects of local scour on failure envelopes of offshore monopiles and caissons

Local scour may induce bearing capacity loss of the foundation significantly by removing soil around the foundation and it has become one of the pivotal factors causing the failure of structures in offshore engineering. Therefore, it is indispensable to investigate the effect of local scour on bearing capacity behaviour of foundations. This paper focuses on the effects of dimensions of local scour hole on both ultimate bearing capacities and failure envelopes of the monopile and the caisson in undrained soil with different soil strength heterogeneity ratios using three-dimensional finite element method. The results show that the scour depth has a more significant effect on the ultimate bearing capacity than the scour hole angle. Meanwhile, the scour depth has a more significant effect on the lateral bearing capacity (i.e., horizontal bearing capacity and moment) than on the vertical bearing capacity. For given dimensions of local scour hole, the effect of local scour on the bearing capacity decreases as soil strength heterogeneity ratio increases. Moreover, local scour affects not only the size of the failure envelopes of the monopile and the caisson, but also their shape. Based on the above findings, a procedure of designing the monopile and the caisson to consider local scour effect is proposed, which could be helpful to the design of the foundations in practical engineering.