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Arabian Journal for Science and Engineering

, Volume 41, Issue 4, pp 1199–1213 | Cite as

Comparison of Local Scour Characteristics around Two Eccentric Piers of Different Shapes

  • Subhasish DasEmail author
  • Rajib Das
  • Asis Mazumdar
Research Article - Civil Engineering

Abstract

Local scour at single pier has been extensively studied by several investigators, but scanty work is available on scour around piers placed in close proximity. The present research is concerned with experimental studies of the formation and characteristics of local equilibrium scour around a set of two identical circular-, square-, and triangular-shaped piers placed in longitudinal direction to the flow with a constant eccentricity (transverse distance). The objective is to see the nature of scour evolved due to the effect of mutual interference of one pier on another with the longitudinal spacing between them varying 0.25, 0.375, 0.5, 0.625, and 0.75 times the scour-affected lengths for a single-pier test. Analysis of the results shows the variations of individual non-dimensional equilibrium scour parameters with the effective pier width (diameter of the smallest circumscribing circle of the pier) and increasing longitudinal spacing between the piers.

Keywords

Open-channel flow Clear water scour Eccentric pier Characteristic pier width Longitudinal spacing 

Notations

ac

Characteristic cross-sectional area of pier inside the water (cm2), \({\pi {b}_{{\rm c}}^{2}}\)

ap

Cross-sectional area of pier (cm2), \({\pi b^{2}}\)

as

Planner surface area of equilibrium scour hole (cm2)

b

Pier diameter or width (cm)

bc

Characteristic pier width (cm), b e K s

be

Effective pier width (cm)

dse

Equilibrium scour depth (cm)

ds

Maximum equilibrium scour depth (cm)

d50

Median diameter of sand (mm)

e

Center-to-center distance between the front and rear piers (cm), 3b

F

Froude number of flow, \({U{/}\sqrt{gh}}\)

h

Approaching flow depth (cm)

Ks

Ratio of the scour depth for any pier to that for the circular pier

l

Longitudinal spacing (along the flow) between the front and rear piers (cm)

lsm

Maximum equilibrium scour length for two-pier arrangement (cm)

lsn

Maximum net scour length for two-pier arrangement (cm), l sml

lss

Maximum equilibrium scour length for single pier (cm)

L

Maximum equilibrium length of sediment transportation (cm)

r

Correlation coefficient

R

Hydraulic radius (cm)

Re

Flow Reynolds number, UR

Rp

Pier Reynolds number, Ub

uc

Critical velocity (cm/s)

\({u_{\ast}}\)

Shear velocity (cm/s)

U

Depth-averaged approaching flow velocity (cm/s)

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Characteristic volume of pier below the water surface level (cm3)

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Volume of pier below the water level (cm3), d sm a p

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Volume of equilibrium scour hole (cm3)

wsm

Maximum scour width for two-pier arrangement (cm)

wss

Maximum scour width for single pier (cm)

ρ

Mass density of water (kg/m3)

\({\rho_{{\rm s}}}\)

Mass density of sand (kg/m3)

\({\sigma_{{\rm g}}}\)

Geometric standard deviation, \({\sqrt{{d_{84}}/{d_{16}}}}\)

ν

Kinematic viscosity (m2/s)

\({\varphi_{r}}\)

Angle of repose (deg)

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Copyright information

© King Fahd University of Petroleum & Minerals 2015

Authors and Affiliations

  1. 1.School of Water Resources EngineeringJadavpur UniversityKolkataIndia

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