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Final Capstone Report after editing

Capstone project
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Capstone Project (UCS797)

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PROJECT REPORT
(February- July 2017)

ANALYSIS OF SCOURING ON CIRCULAR PIERS USING

DIFFERENT EXTENSIONS ATTACHED TO THE PIERS

SUBMITTED BY
HARPREET SINGH 101302037
RAJAT CHAUHAN 101302069
RISHAV RAJ SINGH 101302074
SHUBHAM 101302080
SHUBHAM SHARMA 101302081
TSEWANG GAYLTSEN 101302089
SUBMITTED TO

DR. NAVEEN KWATRA

PROFESSOR & HEAD, CED
THAPAR UNIVERSITY, PATIALA
DEPARTMENT OF CIVIL ENGINEERING
THAPAR UNIVERSITY, PATIALA
(Declared as Deemed-to-be-University u/s 3 of the UGC Act, 1956)
JULY 2017
Capstone Project

DECLARATION

We hereby declare that the group project report entitled “Analysis of scouring on circular pier
using different extensions attached to the pier” is an authentic record of our own work carried out
at Patiala as requirement of Capstone Project in the eighth semester for the award of degree of
B. (Civil Engineering), Thapar University, Patiala, under the guidance of Dr Tapas Karmaker,
during January to May, 2017.
HARPREET SINGH 101302037
RAJAT CHAUHAN 101302069
RISHAV RAJ SINGH 101302074
SHUBHAM 101302080
SHUBHAM SHARMA 101302081
TSEWANG GYALSON 101302089
Date: ___________________
Certified that the above statement made by the student is correct to the best of our knowledge
and belief.
TAPAS KARMAKER
Associate Professor
Faculty Coordinator
Capstone Project

ABSTRACT

A series of bridge failures due to pier scour has kindled our interest in understanding of the
scour process and for developing improved ways of protecting bridges against scour.
The two major countermeasure techniques employed for preventing or minimizing local
scour at bridge piers are increased scour resistance and flow alteration. In the former case, the
objective is to combat the erosive action of the scouring mechanisms using hard engineering
materials or physical barriers such as rock riprap. In the latter case, the objective is to either
inhibit the formation of the scouring mechanisms or to cause the scour to be shifted away
from the immediate vicinity of the pier. This report focuses on a particular application of the
latter technique.
In this study, we used a circular pier attached with different geometric arrangements for
reducing the effects of local scour at a bridge pier.
The overall objective of the project is the:
 Evaluation of the effectiveness of adjustments attached with pier for mitigating the
depth of scour that would otherwise occur at a bridge pier and to measure the scouring
depth caused due to circular pier.
 To analysis the effect on scouring when different extension are used.
 To calculate the velocity vector.
 To calculate Boundary Shear Stress (BSS).
Capstone Project

CONTENTS

S. TOPICS PAGE NO.

1. Declaration 2

2. Acknowledgement 3

3. Abstract 4

4. Chapter 1- Introduction 7

5. Chapter 2- Literature Review 8

6. Chapter 3- Methodology

7. Chapter 4- Result and Analysis

7. Chapter 5 – Conclusion

8. Chapter 6- Matrix and Brief Notes

29 BSS (Top view)

30

Images of scouring with different

adjustments

31 Scour depth at different locations

Table No. Discription Page No.

1 Project Site

2 Pier Discription

3 Specifications of ADV

4

Chapter-

INTRODUCTION

1 GENERAL

Scour is defined as the erosion of streambed around an obstruction in a flow field. The
amount of reduction in the streambed level below the bed level of the river prior to the
commencement of scour is referred as the scour depth. A scour hole is defined as depression
left behind when sediment is washed away from the riverbed in the vicinity of the structure.
Local scour refers to the removal of sediment from the immediate vicinity of bridge piers or
abutments. It occurs due to the interference of pier or abutment with the flow, which results in
an acceleration of flow, creating vortices that remove the sediment material in the immediate
surroundings of the bridge pier or abutment.
Figure 1: Scouring due to pier
The process of scour is affected by a large number of variables. The flow, fluid, pier and
sediment characteristics are the main variables affecting the pier scour time and spacing
between the piers. Depending upon whether the flow approaching the pier is transporting
sediment or not, the pier scour is classified as:
i. Clear-water scour; when approaching flow does not carry any sediment
This type of scour occurs as a result of the construction of a channel or waterway,
either due to a natural means or human alteration of the floodplain. The effect of such
a constriction is a decrease in the flow area and an increase in the average flow
velocity, which consequently causes an increase in the erosive forces exerted on the
channel bed. The overall effect of this phenomenon is the lowering of the channel
bed. A bridge with approaches or abutments encroaching onto the floodplain of a river
is a common example of contraction scour.
iii. Local Scour
This type of scour refers to the removal of sediment from the immediate vicinity of
bridge piers or abutments. It occurs as a result of the interference with the flow by
piers or abutments, which result in an acceleration of the flow, creating vortices that
remove the sediment material in the surroundings of the bridge piers or abutments.
Scour occurring as a result of spur dykes and other river training works is also an
example of local scour. (Figure 2) shows the typical appearance of local scour around
bridge piers.
Figure 2: Scouring in Piers

1.2 Local Scour mechanism

Local scouring takes place due to the formation of vortices and down-flow at the upstream
face of the pier. The flow decelerates as it approaches
the pier coming to rest at the face of the pier. The approach flow velocity, therefore, at the
stagnation point on the upstream side of the pier is reduced to zero, which results in
a pressure increase at the pier face. The associated stagnation pressures are highest near the
surface, where the deceleration is greatest, and decrease downwards.
In other words, as the velocity is decreasing from the surface to the bed, the stagnation
pressure on the face of the pier also decreases accordingly i. a downward pressure gradient.
The pressure gradient arising from the decreased pressure forces the flow down the face of
the pier, resembling that of a vertical jet. The resulting down-flow impinges on the streambed
and creates a hole in the vicinity of the pier base. The strength of the down-flow reaches a
maximum just below the bed level. The down flow impinging on the bed is the main scouring
agent (Figure 3) shows the flow and scour pattern at a circular pier. As illustrated in the
figure, the strong vortex motion caused by the existence of the pier entrains bed sediments
within the vicinity of the pier base. The down flow rolls up as it continues to create a hole
and, through interaction with the oncoming flow, develops into a complex vortex system. The
vortex then extends downstream along the sides of the pier. This vortex is often referred to as
horseshoe vortex because of its great similarity to a horseshoe. Thus the horseshoe vortex
developed as a result of separation of flow at the upstream face of the scour hole excavated
by the down-flow. .The horseshoe vortex itself is a lee eddy similar to the eddy or ground
roller downstream of a dune crest. The horseshow vortex is very effective at transporting the
dislodged particles away past the pier. The horseshoe vortex is as a result of scour but is not
the cause of scour. As the scour depth increases, the horseshoe vortex strength diminishes,
which automatically leads to a reduction in the sediment transport rate from the base of the
pier.
As shown in Figure besides the horseshoe vortex in the vicinity of the pier base, there are also
the vertical vortices downstream of the pier referred to as wake vortices. The separation of
the flow at the sides of the pier produces the so called wake vortices. These wake vortices are
not stable and shed alternately from one side of the pier and then the other. It should be noted,
Factors which affect the magnitude of the local scour depth at piers are:
1. Approach flow velocity
2. Flow depth
3. Pier width
4. Gravitational acceleration
5. Pier length if skewed to the main flow direction
6. Size and gradation of the bed material
7. Angle of attack of the approach flow to the pier
8. Pier shape
9. Bed configuration
10. Ice or debris jams.

1 COUNTER MEASURE

Bend way weirs, spurs and guide banks can help to align the upstream flow while riprap,
gabions, articulated concrete blocks and grout filled mattresses can mechanically stabilize the
pier and abutment slopes. Riprap remains the most common countermeasure used to prevent
scour at bridge abutments. A number of physical additions to the abutments of bridges can
help prevent scour, such as the installation of gabions and stone pitching upstream from the
foundation.
The addition of sheet piles or interlocking prefabricated concrete blocks can also offer
protection. These countermeasures do not change the scouring flow and are temporary since
the components are known to move or be washed away in a flood. FHWA recommends
design criteria in HEC-18 and 23, such as avoiding unfavorable flow patterns, streamlining
the abutments, and designing pier foundations resistant to scour without depending upon the
use of riprap or other countermeasures.
Trapezoidal-shaped channels through a bridge can significantly decrease local scour depths
compared to vertical wall abutments, as they provide a smoother transition through a bridge
opening. This eliminates abrupt corners that cause turbulent areas. Spur dikes, barbs, groynes,
and vanes are river training structures that change stream hydraulics to mitigate undesirable
erosion or deposits. They are usually used on unstable stream channels to help redirect stream
flow to more desirable locations through the bridge. The insertion of piles or deeper footings
is also used to help strengthen bridges.

1 DETAILS OF THE PROJECT

1.4 Project Site

Location Thapar University beside Water Resource Lab
Length of Canal Flume 10000 cm
Width Of canal 76 cm
Type Rectangular Cement canal
Slope 1:
Table 1.
The experiment was to be performed on a rectangular canal (Figure 4) of dimension
(10000x73x55) cm 3 , with slope (1:900). Firstly sand was filled in the canal flume to imitate
scouring due to pier in Natural River.
Figure 5: Instrument extension to hold ADV

1.4 Instrument Used

Acoustic Doppler Velocimeter (ADV) is used to record instantaneous velocity components
at a single-point with a relatively high frequency. Measurements are performed by measuring
the velocity of particles in a remote sampling volume based upon the Doppler shift effect.
Figure 6 (i): ADV Instrument
Figure 6 (ii): ADV Instrument

1.4 Project Objective

The objectives of the project are to:
 Evaluate the effectiveness of adjustments attached with pier for mitigating the depth
of scour that would otherwise occur at a bridge pier and to measure the scouring depth
caused due to circular pier.
 Analyze the effect on scouring when different extension are used.
 Calculate the velocity vector.
 Calculate Boundary Shear Stress (BSS).
previous studies on the use of a collar as a countermeasure for local scour at a bridge pier are
based on experiments carried out using a physical hydraulic model and as such the
practicality of using a collar on the field through a prototype study has not yet been done.

2 CODAL PROVISIONS

As per IRC 78-2014 (STANDARD SPECIFICATIONS AND CODE OF PRACTICE FOR
ROAD BRIDGES SECTION: VII FOUNDATIONS AND SUBSTRUCTURE)
2.1 Mean Depth of Scour
The mean scour depth below Highest Flood Level (HFL) for natural channels flowing over
scour able bed can be calculated theoretically from the following equation:
dsm = 1(Db 2 /Ksf)1/
Where
Db= The design discharge for foundation per metre width of effective waterway.
Ksf = Silt factor for a representative sample of bed material obtained upto
the level of anticipated deepest scour.
2.2 Maximum Depth of Scour for Design of Foundation
The maximum depth of scour below the Highest Flood Level (HFL) for the design of piers
and abutments having individual foundations without any floor protection may be considered
as follows.
Flood without seismic combination (Clause 703.3)
i) For piers - 2 dsm
ii) For abutments - a) 1 .27 dsm with approach retained or lowest bed level
whichever is deeper.
b) 2 dsm with scour all around
Flood with seismic combination
For considering load combination of flood and seismic loads (together with other appropriate
combinations given elsewhere) the maximum depth of scour given in Clause 703.3 .1 may
be reduced by multiplying factor of 0.
Clause 703.3.1 For low water level (without flood conditions) combined with seismic
combination maximum level of scour below high flood level can be assumed as 0 times
scour given in Clause 703.3.

Chapter-

METHODOLOGY

In this chapter, the experimental arrangements, hydraulic models, data acquisition system and
variables measured in the model study are described. All of the experiments were conducted
in Thapar University near water resource lab.
The whole experiment was conducted in a rectangular flume of size (10000x73x55) cm 3.
About 15 cm depth of sand of Zone II was filled. The working section of the flume is made
up of a glass on side walls to facilitate visual observations as shown in the (Figure 7).
Was this document helpful?

Final Capstone Report after editing

Course: Capstone Project (UCS797)

14 Documents
Students shared 14 documents in this course

University: Thapar Institute of Engineering and Technology

Was this document helpful?
PROJECT REPORT
(February- July 2017)
ANALYSIS OF SCOURING ON CIRCULAR PIERS USING
DIFFERENT EXTENSIONS ATTACHED TO THE PIERS
SUBMITTED BY
HARPREET SINGH 101302037
RAJAT CHAUHAN 101302069
RISHAV RAJ SINGH 101302074
SHUBHAM 101302080
SHUBHAM SHARMA 101302081
TSEWANG GAYLTSEN 101302089
SUBMITTED TO
DR. NAVEEN KWATRA
PROFESSOR & HEAD, CED
THAPAR UNIVERSITY, PATIALA
DEPARTMENT OF CIVIL ENGINEERING
THAPAR UNIVERSITY, PATIALA
(Declared as Deemed-to-be-University u/s 3 of the UGC Act, 1956)
JULY 2017
Capstone Project

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