scholarly journals Analysis of scour depth in the case of parallel bridges using HEC-RAS

2020 ◽  
Vol 20 (8) ◽  
pp. 3419-3432
Author(s):  
Darshan J. Mehta ◽  
S. M. Yadav
Keyword(s):  
Scour Depth ◽  
River Engineering ◽  
Flood Events ◽  
Sediment Characteristics ◽  
River Bed ◽  
Scour Holes ◽  
Minimum Depth ◽  
The Stability ◽  
Bridge Foundation ◽  
Hydraulic Stability

Abstract Scour is now one of the main problems for river as well as for coastline engineering. Bridges are the vital structures which must be designed to prevent failure against the effects of scour. Scour holes can occur without warning and cause the failure of a bridge. The main significant issues in hydraulic and river engineering are to determine the connection between parameters affecting the maximum and minimum depth of scour. The scour depth in the alluvial stream below a river bed differs based on the flows, pier shape, pier size and sediment characteristics. Dual bridges of basically the same structure are placed parallel to and only a small distance away from an existing bridge, either on the upstream or downstream side. Naturally, the backwater generated by dual bridges is bigger than that of a single bridge but lower than the value resulting from separate consideration of the two bridges. In the present work, an hydraulic model is used to simulate the stability of a bridge in the study area, namely ‘Sardar Bridge’ on the Tapi river. Scour profiles for various flood events have been assessed for a particular bridge. The velocity of flow is used to estimate depths of scour at different piers and abutments. Estimating depth of the scour during the design can significantly decrease the overall cost of bridge foundation construction. Results from the present study show that construction of a new bridge should be proposed on the upstream side rather than downside side of the existing bridge. By doing so, hydraulic stability of the existing bridge is ensured.

Development of a Three-Dimensional Iterative Methodology Using a Commercial CFD Code for Flow Scouring Around Bridge Piers

2012 ◽  
Author(s):  
Phani Ganesh Elapolu ◽  
Pradip Majumdar ◽  
Steven A. Lottes ◽  
Milivoje Kostic
Keyword(s):  
Shear Stress ◽  
Three Dimensional ◽  
Critical Shear Stress ◽  
Shear Stresses ◽  
Computational Domain ◽  
Time Step ◽  
Mesh Morphing ◽  
River Bed ◽  
Scour Hole ◽  
The Stability

One of the major concerns affecting the safety of bridges with foundation supports in river-beds is the scouring of river-bed material from bridge supports during floods. Scour is the engineering term for the erosion caused by water around bridge elements such as piers, monopiles, or abutments. Scour holes around a monopile can jeopardize the stability of the whole structure and will require deeper piling or local armoring of the river-bed. About 500,000 bridges in the National Bridge Registry are over waterways. Many of these are considered as vulnerable to scour, about five percent are classified as scour critical, and over the last 30 years bridge failures caused by foundation scour have averaged about one every two weeks. Therefore it is of great importance to predict the correct scour development for a given bridge and flood conditions. Apart from saving time and money, integrity of bridges are important in ensuring public safety. Recent advances in computing boundary motion in combination with mesh morphing to maintain mesh quality in computational fluid dynamic analysis can be applied to predict the scour hole development, analyze the local scour phenomenon, and predict the scour hole shape and size around a pier. The main objective of the present study was to develop and implement a three dimensional iterative procedure to predict the scour hole formation around a cylindrical pier using the mesh morphing capabilities in the STARCCM+ commercial CFD code. A computational methodology has been developed using Python and Java Macros and implemented using a Bash script on a LINUX high performance computer cluster. An implicit unsteady approach was used to obtain the bed shear stresses. The mesh was iteratively deformed towards the equilibrium scour position based on the excess shear stress above the critical shear stress (supercritical shear stress). The model solves the flow field using Reynolds Averaged Navier-Stokes (RANS) equations, and the standard k–ε turbulence model. The iterative process involves stretching (morphing) a meshed domain after every time step, away from the bottom where scouring flow parameters are supercritical, and remeshing the relevant computational domain after a certain number of time steps when the morphed mesh compromises the stability of further simulation. The simulation model was validated by comparing results with limited experimental data available in the literature.

UAV Based Multi-Hazard Vulnerability Assessment System for Bridges Exposed to Scour

2020 ◽  
Author(s):  
Okan Özcan ◽  
Orkan Özcan
Keyword(s):  
Load Capacity ◽  
Time History ◽  
Element Model ◽  
Lateral Load ◽  
Assessment System ◽  
Bridge Piers ◽  
Scour Depth ◽  
River Bed ◽  
Principal Axes

<p>Evaluating the multi-hazard performance of river crossing bridges under probable earthquake, flood, and scouring scenarios is a cumbersome task in performance-based engineering. The loss of lateral load capacity at bridge foundations may induce bridges to become highly vulnerable to failure when the effects of scour and floods are combined. Besides, the assessment of local scouring mechanism around bridge piers provides information for decision‐making regarding the pile footing design and for predicting the safety of bridges under critical scoured conditions. Thereby, accurate high-resolution Digital Elevation Models (DEMs) are critical for many hydraulic applications such as erosion, hydraulic modelling, sediment transport, and morphodynamics. In the present study, an automated unmanned aerial vehicle (UAV) based multi-hazard performance assessment system was developed to respond to rapid performance evaluation and performance prediction needs for river crossing reinforced concrete (RC) bridges. The Bogacay Bridge constructed over Bogacay in Antalya, Turkey was selected as the case study. In the developed system, firstly the seasonally acquired UAV measurements were used to obtain the DEMs of the river bed from 2016 to 2019. The transverse cross sections of the river bed that were taken close to the inspected bridge were used to measure the depth of the scoured regions along the bridge piles under the present conditions. Separately, in conjunction with the flood simulation and validation with 2003 flood event (corresponds to Q<sub>50</sub>=1940 m<sup>3</sup>/s), the scour depth after maximum probable flood load according to the return period of 500 years (Q<sub>500</sub>=2560 m<sup>3</sup>/s) were predicted by HEC-RAS software. Afterwards, the 3D finite element model (FEM) of the bridge was constituted automatically with the developed code considering the scoured piles. The flood loads were exerted on the modeled bridge with regard to the HEC-RAS flood inundation map and relevant water depth estimations around the bridge piers. For the seismic evaluation, nonlinear time history analyses (THA) were conducted by using scaled eleven scaled earthquake acceleration records that were acting in both principal axes of the bridge simultaneously by considering maximum direction spectra (SaRotD100) as compatible with the region seismicity. In the analyses; as the scour depth increased, the fundamental periods, shear forces and the bending moments were observed to increase while the pile lateral load capacities diminished. Therefore, the applicability of the proposed system was verified using the case study bridge.</p>

Study of Bridge Foundation Performance Under Dynamic Loading

1974 ◽  
Vol 11 (3) ◽  
pp. 409-419
Author(s):  
Robert B. Dodds ◽  
G. V. Ganapathy
Keyword(s):  
Bridge Piers ◽  
Bridge Structure ◽  
Railway Bridge ◽  
River Bed ◽  
Bridge Responses ◽  
Remedial Work ◽  
Bridge Foundation ◽  
Drill Holes ◽  
Work Done ◽  
Train Loading

Seismographic equipment was used to study the response of a railway bridge under dynamic train loading and thereby to determine the performance of the foundations of the bridge. The same methods were used to determine the effectiveness of remedial work done on the bridge piers and on the subsoil beneath the piers.The bridge was constructed in 1898 and is a three-span, masonry and stone arch bridge, 273 ft (83.2 m) in length. The east abutment is founded on bedrock, however, the west abutment and two piers in the river bed are founded on deep alluvial deposits.Seismographic studies indicated relatively large movements of one pier which were attributed to foundation scouring. A program of grouting the pier subgrade confirmed this assessment. Subsequent seismographic studies confirmed the effectiveness of the remedial works undertaken. The studies of the bridge responses under dynamic train loading provided sufficient data that scour areas beneath a pier could be pinpointed.The technique applied on this project determined bridge pier foundation conditions much more quickly and economically than a normal program of exploratory drill holes. The same technique could be used to assess the behavior of individual components of a bridge structure.

scholarly journals Estimation of maximum scour depth near a spur dike

2016 ◽  
Vol 43 (3) ◽  
pp. 270-278 ◽  
Author(s):  
Manish Pandey ◽  
Z. Ahmad ◽  
P.K. Sharma
Keyword(s):  
Natural Phenomenon ◽  
Scour Depth ◽  
Flowing Water ◽  
Performance Indices ◽  
Spur Dike ◽  
Bed Erosion ◽  
River Bed ◽  
Spur Dikes ◽  
Dike Failure ◽  
Better Than

Scour is a natural phenomenon in rivers caused by the erosive action of the flowing water on the bed and banks. Spur dikes are constructed across the flow to protect the bank from erosion by shifting of the river away from the bank. The spur dike undermines due to river-bed erosion and scouring, which is generally recognized as the main cause of spur dike failure. In this study, accuracy of existing equations for the computation of maximum scour depth has been checked with available data in the literature and data collected in the present study using graphical and statistical performance indices. Three new relationships are also proposed to estimate the maximum scour depth and maximum scour length upstream and downstream of spur dike. This new relationship for maximum scour depth is shown to perform better than other existing equations.

Soil failure in shallow covers above flexible conduits

1983 ◽  
Vol 10 (4) ◽  
pp. 654-661 ◽  
Author(s):  
Hisham Hafez ◽  
George Abdel-Sayed
Keyword(s):  
Soil Cover ◽  
Stress Transfer ◽  
Critical Limit ◽  
Element Analysis ◽  
Soil Failure ◽  
Failure Propagation ◽  
Live Loads ◽  
Minimum Depth ◽  
The Stability ◽  
Good Agreement

Field experience has shown that shallow soil covers above large flexible conduits may fail under concentrated live loads. To avoid such failure, an empirical minimum depth of cover of one-sixth of the span of the conduit is required by the design codes, irrespective of the shape of the conduit.The present paper examines the stability of the soil cover using a finite-element analysis in which the soil stresses are calculated in the upper zone of the mesh. Failure in a soil element is determined using Mohr–Coulomb criteria. A stress transfer technique is used to distribute the stresses exceeding the failure limit between neighbouring elements. Failure propagation is detected when the live load reaches a critical limit. Analytical results are in good agreement with laboratory test results.A parametric study shows that the stability of soil cover is governed by height of cover, conduit shape and size, and the eccentricity of the live axle loads. It also shows that the present code requirements are not adequate for horizontal ellipses, and are too conservative for vertical ellipses.

scholarly journals Causes and mechanisms of the destruction of the red river banks in Hanoi

2020 ◽  
pp. 88-93
Author(s):  
T. H. Dinh ◽  
O. E. Vyazkova ◽  
I. K. Fomenko ◽  
S. V. Kozlovskiy
Keyword(s):  
Friction Angle ◽  
Red River ◽  
Economic Activities ◽  
River Bed ◽  
Landslide Processes ◽  
Dry Seasons ◽  
Lateral Erosion ◽  
The Stability ◽  
The City ◽  
River Banks

The coastal territories of the Red River, passing through the city of Hanoi (the capital of Vietnam), are developed very dynamically by different types of construction, sand extraction from the river bed and its banks, pumping of water, creation of ponds and agriculture. But these activities are only possible in areas protected against annual floods with a dam. However, in recent years, the intensity of lateral erosion of the river and associated suffocation and landslide processes has become rapidly increasing in both flood and dry seasons. Deformations capture natural river banks and the dam body. The authors analysed the causes and identified mechanisms of these processes taking into account variable climatic, tectonic, hydrological, geological and hydrogeological conditions complicated by economic activities in the coastal zone. The article provides calculations of the stability of banks in different conditions (during and after the flood), which confirms theoretical ideas about the mechanism of the process and coincide with the observations. The greatest contribution to the banks destruction is the variability of the internal friction angle of the sands entering the section of the coastal territory.

scholarly journals Experimental Scours by Impinging Twin-Propeller Jets at Quay Wall

2020 ◽  
Vol 8 (11) ◽  
pp. 872
Author(s):  
Yonggang Cui ◽  
Wei Haur Lam ◽  
Zhi Chao Ong ◽  
Lloyd Ling ◽  
Chee Loon Siow ◽  
...  
Keyword(s):  
Scour Depth ◽  
Water Tank ◽  
Quay Wall ◽  
Depth Position ◽  
Scour Hole ◽  
Scour Holes ◽  
Horseshoe Vortices ◽  
Three Stages ◽  
Deposition Height ◽  
The Relationship

Experiments were conducted to investigate the seabed scour holes due to the interaction between the twin-propeller jet and quay wall. Vertical quay wall was modelled by using a polyvinyl chloride (PVC) plastic plate in a water tank. The relationship between the positions of the propeller and the vertical quay wall was designed according to the actual working conditions of a ship entering and leaving a port. Propeller-to-wall distance and rotational speed were changed to observe the various scour conditions. The scour depth was measured by using an Acoustic Doppler Velocimeter (ADV). Primary scour hole was found within the jet downstream and secondary scour hole occurred beneath of the propeller. Third scour hole was found close to the quay wall due to horseshoe vortices. The maximum scour position of this third scour hole was found at the jet centre near the quay wall. Temporal formation of scour holes can be divided into three stages: axial scour formation, obstructed scour expansion and equilibrium stages. The quantitative relationships for six characteristic parameters of the scour pit were established including the maximum scour depth (εmax,q), maximum scour depth position (Xm,q), maximum scour width (Wm,q), length of main scour pit (XS,q), maximum deposition height (ZD,q), and location of maximum deposition height (XD,q).

Spatiotemporal response of an Alpine braided river reach to snow melt and flood events

2020 ◽  
Author(s):  
Maarten Bakker ◽  
Florent Gimbert ◽  
Clément Misset ◽  
Laurent Borgniet ◽  
Alain Recking
Keyword(s):  
Morphological Change ◽  
Return Period ◽  
Temporal Dynamics ◽  
Bedload Transport ◽  
Snow Melt ◽  
Braided River ◽  
Flood Events ◽  
River Bed ◽  
Extreme Flood ◽  
Braided Reach

<p>Alpine environments are responding to accelerated climate warming through the release and mobilization of large amounts of unconsolidated sediment. Sediment fluxes delivered to Alpine streams may be buffered, filtered and/or modulated as they pass through braided river reaches, which play a key role in the downstream transfer and dynamics of bed material. The functioning of these braided reaches is however still poorly understood, particularly during high magnitude events whose effects are very difficult to monitor but play an ever more prominent role in river system evolution.</p><p>In this study, we investigate the transfer of bedload material and river bed morphological change in a braided reach of the Séveraisse River (France), over the course of the melt season and two large flood events with an estimated return period of 5 and 50 years. To quantify braided reach dynamics, a multi-physical approach is employed that combines both temporally and spatially resolved techniques. We use bank-side geophones and locally derived parameters that describe seismic wave propagation in the subsurface to accurately quantify bedload transport and gain a unique insight in its temporal dynamics, particularly during the flood events. River bed elevation changes are determined from intermittent UAV-based LiDAR and photogrammetric acquisition. These are complemented with hourly (daytime) time-lapse images that register planform changes during the flood events.</p><p>Our results show strongly contrasting morphodynamic behavior with different flow conditions. During ‘normal’ bedload transport conditions driven by annual snow-melt, channel aggradation occurs leading to progressively lower bedload export from the reach for a given discharge. During the flood with a 5 year return period, which occurred at the end of the melt season, the braided riverbed morphology is rearranged and net sediment export took place. Most interestingly, in the autumn an extreme flood event led to the development of a single channel, meandering planform with significant outer bend erosion on alternating banks. Although this morphological change may be only temporary, i.e. a braided configuration may be expected to be gradually re-instated, it has important implications on the general functioning and morphological evolution of the reach and the downstream transfer of sediment.</p>

Local Scouring Characteristics Downstream of Arched Cross-Vane Structures

2020 ◽  
Author(s):  
You-Wei Lai ◽  
Po-An Chen ◽  
Hsun-Chuan Chan
Keyword(s):  
Numerical Model ◽  
Flow Rate ◽  
Scour Depth ◽  
Negative Effects ◽  
Scour Holes ◽  
The Cross ◽  
Type 3 ◽  
Geometrical Dimensions

<p>Groundsill is one of the hydraulic structures used to stabilize the riverbed and prevent the erosion of riverbank. Therefore, groundsill may have the negative effects on the ecological environment. Comparing with a traditional groundsill, a Cross-Vane concentrates the water flow and create a downstream pool. This may improve the diversity of the aquatic habitats. The aim of this research is to analyze the scour phenomena and morphologies downstream of an arched Cross-Vane with different geometrical dimensions in a straight channel by using the numerical model. The riverbed slopes of 0%, 2%, 4% and 6% were tested. Among them, the ratio (<em>L/B</em>) between the arc length of the structure (<em>L</em>) and the channel width (<em>B</em>) represents the camber of structures, including 13 kinds of arches. For each arch structure, Densimetric Froude numbers (<em>F<sub>d</sub></em>) , approach flow depths (<em>h<sub>0</sub></em>) and drop heights (<em>Δy</em>) were tested in different flow rate, and the flow rate was between 0.01cms and 0.04cms.The results showed the downstream scour pattern of the arched Cross-Vane had a significant correlation with <em>F<sub>d</sub></em> and <em>Δy</em>, and could be classified according to the scour length (<em>l<sub>m</sub></em>) and the ridge length (<em>l<sub>n</sub></em>). Scour typology included five types of scour. Type 1 : <em>l<sub>m</sub>/B</em> > 2.5 and <em>l<sub>n</sub> /B</em> < 1. Type 2: <em>l<sub>m</sub>/B</em> was located about 2.0 to 2.5 and l<em><sub>n</sub>/B > 1. </em>Type 3: <em>l<sub>m</sub>/B=</em>2.0 and<em> l<sub>n</sub>/B</em> < 1. Type 4: <em>l<sub>m</sub>/B</em> was located about 1.5 to 2.0 and <em>l<sub>n</sub>/B</em> > 1. Type 5 : <em>l<sub>m</sub>/B</em> < 1.5 and<em> l<sub>n</sub> /B</em> > 1. <em>L/B</em> was one of the most important parameters affecting the maximum scour depth and its position. When <em>L/B</em> was less than 1.4, the scour holes were similar to the traditional groundsill. When the<em> L/B</em> ranged between 1.4 and 2.3, the maximum scour depth was located at about 0.5 to 0.65 times of scour length downstream the Cross-Vane. When<em> L/B</em> was greater than 2.3, the maximum scour depth was located adjacent to the Cross-Vane.</p><p><strong>Keyword : </strong>Cross-vane, Scour morphology, Numerical model</p>

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