Observations on initiation of pier scour and equilibrium scour hole profiles in cohesive sediments

In this review article, the current status of research on pier scour under waves is presented. This includes a summary of different bridge failure events due to scour, scour mechanism, scour depth predictors under waves, influence of pier shape on scour depth formation, shape of scour hole around piers, and many others. Further, this article describes the scour process, development of scour depth predictors, and the complexity involved in the scour related calculations. Finally, the future scope of research is delineated.

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Overtopping breaching of river levees constructed with cohesive sediments

10.5194/nhess-2015-353 ◽

2016 ◽

Author(s):

H. Y. Wei ◽

M. H. Yu ◽

D. W. Wang ◽

Y. T. Li

Keyword(s):

Soil Properties ◽

Discharge Coefficient ◽

Flow Model ◽

Cohesive Sediments ◽

Flow Shear ◽

Flow Rates ◽

Side Slope ◽

Weir Flow ◽

Scour Hole ◽

Headcut Retreat

Abstract. Experiments were conducted in a bend flume to study the overtopping breaching process and the corresponding overflow rate of river levees constructed with cohesive sediments. The river and land regions were separated by the constructed levee model in the bend flume. Results showed that the levee breaching process can be subdivided into a slope erosion stage, a headcut retreat stage and a breach widening stage. Mechanism such as scour-hole erosion, flow shear erosion, impinging jet erosion, side slope erosion and cantilever collapse were discovered in the breaching process. The erosion characteristics were determined by both flow and soil properties. Finally, the levee breaching flow rates were simulated by a depth averaged 2-D flow model. The calculated overflow rates can be well expressed by the broad-crested weir flow formula. The deduced discharge coefficient was smaller than that of common broad-crested rectangular weirs because of the shape and roughness of the breach.

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Optimal Octagonal Hooked Collar Countermeasure to Reduce Scour Around a Single Bridge Pier

Periodica Polytechnica Civil Engineering ◽

10.3311/ppci.15966 ◽

2020 ◽

Author(s):

Rashid Farooq ◽

Abdul Razzaq Ghumman ◽

Muhammad Atiq Ur Rehman Tariq ◽

Afzal Ahmed ◽

Khan Zaib Jadoon

Keyword(s):

Cross Section ◽

Vital Role ◽

Bridge Pier ◽

Scour Depth ◽

Clear Water ◽

Action Current ◽

Pier Scour ◽

Uniform State ◽

Scour Hole ◽

New Equation

Pier modification countermeasures are essential as they play a vital role in protecting pier against local scour action. Current study investigates experimentally the scour around vertical pier of octagonal cross section with pier modification such as newly proposed octagonal hooked collar is explored, in steady uniform state, under clear water condition. The results of pier scour without any modification were used as a reference to compute the efficiency of hooked collar provision around octagonal pier. The results show that by increasing the hooked collar width up to 2.5 Wp reduced maximum scour depth significantly. However, the experimental investigation revealed that the best combination to be with a hooked collar width of 2.5 Wp, having sidewall height 0.45 Wp. The best combination minimized around 73.3 % of scour hole depth, compared to octagonal pier without any modification. Using experimental results, a new equation is proposed to predict the scour depth around a bridge pier fitted with hooked collar. Moreover, a relation was developed for maximum scour depth and scour hole volume. Results indicate that the scour hole volume around a bridge pier increases quadratically with maximum scour depth.

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Efficient non-hydrostatic modelling of flow and bed shear stress in a pier scour hole

Canadian Journal of Civil Engineering ◽

10.1139/cjce-2013-0160 ◽

2014 ◽

Vol 41 (5) ◽

pp. 450-460 ◽

Cited By ~ 2

Author(s):

S. Pournazeri ◽

S.S. Li ◽

F. Haghighat

Keyword(s):

Experimental Data ◽

Shear Stress ◽

Local Maximum ◽

Bedload Transport ◽

Bed Shear Stress ◽

Pier Scour ◽

Law Of The Wall ◽

Scour Hole ◽

The Law ◽

Wall Method

Predicting 3-D flow in a pier scour hole and the associated bed shear stress τb is important for the safe and economical design of bridge piers. This paper combines layered, hydrostatic hydrodynamic computations with non-hydrostatic pressure corrections, exploring a new modelling approach for efficient and reliable predictions of 3-D flow velocity. The law of the wall method is used for estimating τb. Its suitability for incorporation into layered models for bedload transport and pier scour simulations is also discussed. The predicted flow shows realistic features: strong downward flow adjacent to the upstream nose of a circular pier, vortex motions in the vertical and horizontal direction, and meandering flow wakes. The velocity results compare well with available experimental data. In the approach region, τb is uniform. It attains a local maximum immediately before flow enters the scour hole and then drops non-linearly in the scour-hole region toward the pier. In the wake region, τb has very low values. The τb predictions are consistent with the experimental data. In multi-layer models, when applying the law of wall method, one should use near-bed velocities as opposed to bottom-layer velocities to obtain more reliable τb estimates and avoid noisy results, which can cause a numerical instability problem in bedload transport simulations.

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BRIDGE PIER SCOUR: A REVIEW OF PROCESSES, MEASUREMENTS AND ESTIMATES

Environmental Engineering and Management Journal ◽

10.30638/eemj.2012.121 ◽

2012 ◽

Vol 11 (5) ◽

pp. 975-989 ◽

Cited By ~ 29

Author(s):

Luigia Brandimarte ◽

Paolo Paron ◽

Giuliano Di Baldassarre

Keyword(s):

Bridge Pier ◽

Pier Scour ◽

Bridge Pier Scour

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Design options for self-cleansing storm sewers

Water Science & Technology ◽

10.2166/wst.1996.0214 ◽

1996 ◽

Vol 33 (9) ◽

pp. 215-220 ◽

Cited By ~ 17

Author(s):

Chandramouli Nalluri ◽

Aminuddin Ab. Ghani

Keyword(s):

Cohesive Sediments ◽

Stress Criterion ◽

Sediment Bed ◽

Sediment Size ◽

Codes Of Practice ◽

Design Charts ◽

Design Options ◽

Minimum Velocity ◽

Limited Depth ◽

Storm Sewers

A list of available codes of practice for self-cleansing sewers is presented and a review of appraisals of minimum velocity criterion is summarised. Comparisons of newly developed “minimum velocity” criteria and “minimum shear stress” criterion are presented. Some design charts are also given. These charts are applicable to non-cohesive sediments (typically storm sewers). It appears that sediment size and concentration need to be taken into account, and that a limited depth of sediment bed is recommended for large pipes (diameters > 1000 mm) to maximise their transport capacity.

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Pickup rate of non-cohesive sediments in low-velocity flows

Journal of Hydraulic Research ◽

10.1080/00221686.2020.1871430 ◽

2021 ◽

pp. 1-11

Author(s):

Dake Chen ◽

Bruce Melville ◽

Jinhai Zheng ◽

Yigang Wang ◽

Chi Zhang ◽

...

Keyword(s):

Cohesive Sediments ◽

Low Velocity

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A Computationally Efficient Shallow Water Model for Mixed Cohesive and Non-Cohesive Sediment Transport in the Yangtze Estuary

Water ◽

10.3390/w13101435 ◽

2021 ◽

Vol 13 (10) ◽

pp. 1435

Author(s):

Peng Hu ◽

Junyu Tao ◽

Aofei Ji ◽

Wei Li ◽

Zhiguo He

Keyword(s):

Sediment Transport ◽

Yangtze Estuary ◽

Water Model ◽

Cohesive Sediments ◽

Shallow Water Model ◽

Computationally Efficient ◽

Time Step ◽

The Yangtze Estuary ◽

Erosion Coefficient ◽

Cohesive Sediment Transport

In this paper, a computationally efficient shallow water model is developed for sediment transport in the Yangtze estuary by considering mixed cohesive and non-cohesive sediment transport. It is firstly shown that the model is capable of reproducing tidal-hydrodynamics in the estuarine region. Secondly, it is demonstrated that the observed temporal variation of suspended sediment concentration (SSC) for mixed cohesive and non-cohesive sediments can be well-captured by the model with calibrated parameters (i.e., critical shear stresses for erosion/deposition, erosion coefficient). Numerical comparative studies indicate that: (1) consideration of multiple sediment fraction (both cohesive and non-cohesive sediments) is important for accurate modeling of SSC in the Yangtze Estuary; (2) the critical shear stress and the erosion coefficient is shown to be site-dependent, for which intensive calibration may be required; and (3) the Deepwater Navigation Channel (DNC) project may lead to enhanced current velocity and thus reduced sediment deposition in the North Passage of the Yangtze Estuary. Finally, the implementation of the hybrid local time step/global maximum time step (LTS/GMaTS) (using LTS to update the hydro-sediment module but using GMaTS to update the morphodynamic module) can lead to a reduction of as high as 90% in the computational cost for the Yangtze Estuary. This advantage, along with its well-demonstrated quantitative accuracy, indicates that the present model should find wide applications in estuarine regions.

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