Effect of Interaction between Bridge Piers on Local Scouring in Cohesive Soils

Zahraa F Hassan,Abdul-Hassan K Al-Shukur,Ibtisam R Karim

doi:10.28991/cej-2020-03091498

Zahraa F Hassan, Abdul-Hassan K Al-Shukur + Show 1 more

Open Access

https://doi.org/10.28991/cej-2020-03091498

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Abstract

Local scour at the piers is one of the main reasons of bridge foundation undermining. Earlier research studies focused mainly on the scour at a single bridge pier; nevertheless, modern designs of the bridges comprise wide-span and thus group of piers rather than a single pier are usually used to support the superstructure. The flow and scour pattern around group of piers is different from the case of a single pier due to the interaction effect. Reviewing the literature of local scour around bridge piers group revealed that the local scour around bridge piers group founded in cohesive soil bed was not investigated, and most of the scour studies were related to scour in cohesionless soils. The objective of the present study is to investigate the effect of the interaction between two in-line (tandem) circular bridge piers of variable spacings founded in cohesive soil on the local scour. A set of laboratory flume experiments were conducted under the clear-water scour condition to investigate this effect. This study is the first that investigates experimentally the scour around group of bridge piers in cohesive bed. It was found that the maximum scour depth at the upstream pier of the two in-line piers occurred at a spacing of two times the diameter of the pier, scour at the downstream pier was reduced due to a sheltering effect, the interference effect will be reduced for pier spacings larger than three times of the pier diameter. A recent pier scour equation was used to estimate the scour depths at the two in-line piers in cohesive soil and compare the estimated value with the measured scour depths in the laboratory. The comparison indicated that the proposed scour equation overestimates the scour depths at both the upstream and the downstream pier.

Highlights

Local scour around the piers and abutments of bridges is a primary risk of structural instability and collapse
There are a considerable number of research studies about the scour and flow structures around a single bridge pier, on the other hand fewer researches were done about the scour and flow field around group of piers
It was reported in the literature that the local scour hole around a single bridge pier founded in sand starts at the front of the pier and propagates to the downstream and the maximum scour depth is observed at the pier sides

Summary

Introduction

Local scour around the piers and abutments of bridges is a primary risk of structural instability and collapse. Local scour occurs due to the erosive action of the flowing water that excavates and carries away the soil from around the bridge piers and abutments when they are constructed in erodible beds. From the results of the experimental runs, the effect of pier spacing on scour depth was quantified using empirical formulae. Those formulae were developed considering clear water scour, one pier arrangement, one case of flow shallowness and one bed material type. Nazariha [4] investigated local scouring at groups of bridge piers with the aim of developing design relationships for the prediction of local scour under clear water steady uniform current. The developed equations involved two important parameters describing the group effect, these are pier spacing to pier diameter ratio and the flow attack angle

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