EXPERIMENTAL STUDY OF BRIDGE PIER SHAPE TO MINIMIZE LOCAL SCOUR

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International Journal of Civil Engineering and Technology (IJCIET)
Volume 7, Issue 1, Jan-Feb 2016, pp. 162-171, Article ID: IJCIET_07_01_013
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EXPERIMENTAL STUDY OF BRIDGE PIER
SHAPE TO MINIMIZE LOCAL SCOUR
Dr. Abdul-Hassan K. Al-Shukur
Prof., Civil Engineering Department, College of Engineering,
University of Babylon, Hilla- Iraq
Zaid Hadi Obeid
MS.c Candidate, Civil Engineering Department, College of Engineering,
University of Babylon, Hilla- Iraq
ABSTRACT
The study of local scour around bridge piers is very important for safe
design of piers and other hydraulic structures. In this study, shape of pier is
the main concern with three different velocities (0.18, 0.25, and 0.3) m/sec and
other parameters like flow depth, bed material and etc. are remain same for
all experiments. The experiments were conducted using laboratory flume,
operated under the clear water condition using sand as a bed material. The
test program was done on ten different shapes, Circular, Rectangular,
Octagonal, Chamfered, Hexagonal, Elliptical, Sharp, Joukowsky, Oblong,
streamline. were used to investigate the effect of the bridge pier's shape on
local scour to conclude the optimal shape that gives minimum depth of scour.
Comparison of results show that scour at upstream is directly proportional to
exposed area of upstream nose of pier. The results showed that the
rectangular pier gives the largest scour depth (7.6) cm, while the streamline
shape gives the lowest scour depth (3) cm. The equilibrium scour depth of pier
models compared with theoretical equations has been developed by some
researchers and the results were very close.
Key words: Local Scour, Shape of Bridge Pier, Sand Bed
Cite this Article: Dr. Abdul-Hassan K. Al-Shukur and Zaid Hadi Obeid,
Experimental Study of Bridge Pier Shape To Minimize Local Scour,
International Journal of Civil Engineering and Technology, 7(1), 2016, pp.
162-171.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=7&IType=1

Experimental Study of Bridge Pier Shape To Minimize Local Scour
1. INTRODUCTION
Scour is the lowering of the riverbed level by water erosion such that there is a
tendency to expose the foundations of a bridge. The foundation of any hydraulic
structure should be given the greatest importance in design and analysis as compared
with other parts of the structure, because the foundation failure would destroy the
whole structure. Local scour around bridge piers can cause a serious structural
damage to a bridge by eroding the soil bed and destroys the foundation. The collapse
of bridges can lead to significant damages can result in dangerous injuries or death.
Scour problem in New Zealand causes on average every year one bridge failure
(Melville and Coleman, 2000). Arneson et al., 2012 quoted a study Conducted in
1973 for Federal Highway Administration (FHWA) of 383 bridge collapse because of
flooding, 25% of pier damage and 75% of abutment damage. Also in 1987, floods
have been occurred in New York and New England were destroyed and damaged
about 17 bridges (Hamil, 2000).
Different factors affect the process of scour around bridge piers and the flow
pattern. This study focused on the influence of the bridge piers shapes on minimizing
the local scour. The shape of pier is one of the important factors that play an
important role in the creation and the strength of the vortex system. The system of
vortex consists of horseshoe vortex, wake vortex system, trailing vortex system, and
bow wave vortex (Chiew, 1984). There are two types of piers, uniform (simple) piers
and non-uniform piers (complex). Uniform piers are piers having a constant section
throughout their depth and non-uniform piers include piers of piled foundations, slab
footings, and tapered piers (Melville and Coleman, 2000). This study is limited to
only uniform piers and their effects on the depth of local scour.
Tison, 1940 and 1961 (quoted from Breusers et al., 1977) tested the influence of
alignment and shape of pier on local scour in sand (d50 = 0.48) mm. He observed that
the rectangular shape, the maximum scour depth. When the pier aligned with the flow,
he observed that there is no influence of rectangular pier length on scour depth.
Jueyi et al., 2010 identified clear-water scour around semi-elliptical abutments
with armored beds. Experimental study has been carried out under a clear-water scour
condition to explore the local scour around semi-elliptical model bridge abutments
with armor-layer bed, compared with the local scour process around semi-circular
abutment. The researcher concluded that for both semi-elliptical and semi-circular
abutments, with increase in flow velocity in all of the runs the equilibrium scour depth
of the scour hole will be increased.
2. EXPRIMENTAL SETUP
2.1. Laboratory Flume
In order to achieve the mentioned purpose in this study, ten different pier shapes,
rectangular, circular, oblong, hexagonal, octagonal and streamline were operated
under clear water conditions in sand bed material. These models, located in the
hydraulic laboratory of Kut Technical Institute, Iraq. The experiments are conducted
in a flume with a closed-loop flow system. The flume is 12 m in length and 0.5 m in
width. It has toughened transparent glass side walls with height of 45 cm. The general
view of experimental flume shown in Photo 3.1. The working section 4.8 m was
divided into two parts of 2.4 m, the second part filled with erodible uniform sand with
depth 0.1 m. The inlet and outlet of working section contain raised gravels sloping
ends of 1: 17 and 1: 20 respectively to provide uniform flow in test .The discharge

Dr. Abdul-Hassan K. Al-Shukur and Zaid Hadi Obeid
was measured by a V- notch fitted at the flume inlet. A moveable vertical gate is
installed at the downstream to regulate tail-water depth. All depth measurements are
carried out using two movable carriages with point gauges were mounted on brass rail
at the top of flume sides, which have an accuracy of ± 0.1 mm. The velocity of flow
was checked and measured by mini-water velocity meter of accuracy ±2% the
velocity meter measures with a range (0 to 5) m/sec.
Figure 1 The used flume.
2.2. Pier Models
In this study, ten pier shapes was compared with each other, and no any attempt is
made to simulate a real prototype. Piers were manufactured from 18 mm Medium
Density Fiberboard (MDF) sheets. For high accuracy in models dimensions, the
(MDF) sheets have been cutting by using a CNC routing machine. The MDF wood
sheets were then glued and laminated together, painted with pigments and coated with
varnish to increase its smoothness and to avoid MDF swelling of water.
Figure 2 Piers models used in the experiments.

The pier models have a constant length to width ratio with (length/width=4). The
experiments are conducted with a pier width of (4.5cm) at constant flow depth of 0.12
m by changing the shape of pier. According to Chiew and Melville, 1987
recommendations, pier diameter should not be more than 10% of flume width to avoid
wall effect on scouring. In this study, it is kept in mind that the width of the
experimental flume is more than 10 times of the pier width, which satisfies the all
criterion given by above researchers.
2.3. Bed Material
Mechanical sieve analysis test was carried out to characterize the sand bed material
used for study. The results of the test showed that the material of bed with a median
particle size (d50) of 0.71 mm. The geometric standard deviation of the sand size, σg,
is 1.14, which implies that the sand is of uniform size distribution. The σg is defined
as, σg = (d84/d16)0.5
. The plot of the grain size distribution test is depicted in Figure
3.5. The pier diameter was also carefully chosen so that there was negligible effect of
sediment size on the depth of scour. It is known that the bed material grain size does
not affect the depth of scour if the pier width to grain size ratio exceeds a value of
about 25 (Melville, 1997). For this study, the ratios are about 63.4 for the pier of 45
mm, which satisfies the criterion of Melville, 1997.
Figure 3 Grain size distribution curve.
2.4. Experimental Procedure
The following procedure was adopted for all experiments, which performed on steady
subcritical flow at clear water condition with plain bed, i.e., no formation of ripple or
dune through upstream portion at the working section:
0
10
20
30
40
50
60
70
80
90
100
0.1 1
Percentagefiner%
Grain size (mm)

 Pier models was fixed vertically to its place (within the middle of the working
section).
 Bed of working section filled with a layer of sand with thickness of 10 cm.
 Bed surface was leveled using a scraper. Levels are also checked by using the point
gauge.
 Tail gate is raised and the working area is filled with water by hose from the
downstream portion of the flume in order to allow any air bubble to percolate out of
the bed to avoid any settlement around the piers and to prevent any abrupt high
velocity which causes the disturbance in sand bed after starting pumping.
 After starting pumping the tail gate is gradually lowered until the required water
depth established in the flume. This depth is checked by a point gauge and the
velocity also, checked by the velocity meter. The test is conducted over six hours.
 Time was recorded using a stopwatch during each test and at the end of time the flow
is stopped then the scour depth is recorded using a point gauge.
 The flume drained slowly to avoid any change of the scour hole, the sand is allowed
to dry and then the required measurements of sand bed upstream, downstream,
longitudinally, and transversely are recorded.
 The sand was then re-leveled and the steps from (1) through (7) were repeated by
changing the pier shape.
3. TEST PROGRAM
The test program was developed to deal with the pier shape as a mitigation technique
against local scour, with a major focus on the time required to achieve an equilibrium
scour condition. The test program was done on ten different shapes, Circular,
Rectangular, Octagonal, Chamfered, Hexagonal, Elliptical, Sharp, Joukowsky,
Oblong, streamline. Experiments were conducted under clear-water conditions at
different water discharges 10.9 lit/sec, 15.42 lit/sec and 18 lit/sec and maximum depth
of scour was measured. The test conditions for each shape of bridge piers are
summarized in Table 1.
Table 1 Test condition for test series.
NO.
FLOW
INTENSITY
Y (CM) VELOCITY
IN FLUME
Q (LIT/SEC) FR RE
1 0.56 12 0.18 10.9 0.166 14742
2 0.79 12 0.25 15.42 0.230 20817
3 0.92 12 0.30 18 0.276 24300
4. RESULTS
The summary of laboratory results that have been obtained from series tests
conducted on the ten pier shapes are shown in Table 2. The figures 4,5,6,7 are the best
shapes that gave the minimum scour depth while the figure 8 shows the contours line
of scour hole around the best shapes in this study for maximum velocity (0.3) m/sec.
The experiment study showed that scour drastically reduced with changing the pier
shape and increasing with increases flow velocity. The results showed that the
rectangular pier gives the largest scour depth (7.6) cm, while the streamline shape
gives the lowest scour depth (3) cm.

Table 2 Measured scour depths of piers for tests series.
Pier Shape
V=0.18 V=0.25 V=0.3
Measured scour
depth (cm)
Measured scour
depth (cm)
Measured scour
depth (cm)
Circular 3.9 6.1 6.9
Rectangular 4.3 6.8 7.6
Octagonal 4.2 5.2 5.9
Joukowsky 4.7 5.5 6.1
Chamfered 4.1 5.9 6.7
Oblong 4.1 4.6 5.8
Elliptical 3.6 4.9 5.6
Sharp nose 3 4.5 4.9
Hexagonal 2.8 3.6 4.1
Streamline 1.9 2.6 3
Figure 4 Scour pattern developed by minimum and maximum flow intensity
(elliptical pier).

Figure 5 Scour pattern developed by minimum and maximum flow intensity (sharp
nose pier).
Figure 6 Scour pattern developed by minimum and maximum flow intensity
(hexagonal pier).
Figure 7 Scour pattern developed by average and maximum flow intensity
(streamline pier).

Figure 8 Scour contours for maximum flow intensities
5. DISCUSSION
The formation of horseshoe and wake vortices depends on shape of pier. Therefore,
main intention of study was to investigate effect of pier's shape as protecting measure
against local scour. Through a series of experiment on different shapes like
rectangular, Oblong, Hexagonal, Elliptical, sharp and Streamline etc, it was observed
that streamline pier is best protecting measure against local scour instead of other
conventional shapes like rectangular, oblong etc. Theoretical explanation for it, the
piers being an obstruction creates stagnation zone therefore when high velocity flow
impact upstream side of pier it creates velocity jet that moves downward direction and
creates scour hole. Although hexagonal and sharp pier also looks a like streamline
with minimum upstream nose area, presence of corner causes higher scour at corner
itself. It was observed that sharp pier and hexagonal pier's corner are starting point of
local scour which propagates around the pier. For streamline pier, it was observed that
scour started merely from upstream face and ends at mid section. Through this
experimental observations it was concluded that rectangular pier have higher scour
depth as compare to other shapes because of the maximum exposed area and
streamline pier have lower scour depth because of the minimum exposed area. In an
effort to analyze the data from this study further, Colorado state university (CSU) and
Breusers et al., 1977, common equilibrium scour depth prediction equations as
published in the literature were used to compare and compute the equilibrium scour
depth to be expected for the test conditions applicable to each pier geometry. The
reason for the analysis is to evaluate the usefulness of some of the famous equations

in the literature with a view of testing how reasonably they can predict the equilibrium
scour depth based on the flow and sediment conditions used in this study. CSU and
Breusers et al., 1977 formulas can be written as shown in equations 1 and 2,
respectively.
Where: Ksh is the shape factor, it is a function of pier (length/width) in Breusers et
al., 1977 equation, Fr is Froude number, b is the pier width and y is the flow depth.
Comparative results are shown in table 3. The parameters (flow depth, Froude
number, pier width) were constant for all geometries except shape factor was variable.
The shape factors were taken from different researchers including Tison, 1940,
Laursen and Toch, 1956, Chabert and Engeldinger, 1956, Garde, 1961, Larras, 1963,
Venkatadri et al., 1965, Dietz , 1972, Neill, 1973, Ettema,1980 and Richardson and
Davis, 1995, except the shape factors of hexagonal and octagonal shapes, there are no
values available in the literature. The values of measured scour depth agreed well with
the values of theoretical equations that used in this study.
Table 3 Comparison with Colorado state university (CSU) and Breusers et al. (1977)
formulas (V=0.3 m/sec).
6. CONCLUSIONS
The conclusions of this study were:
 Equilibrium depth of scour and initial scour rate depends on pier shape. Rectangular
pier has a maximum exposed area that's why scour depth is much higher (7.6) cm
than others shapes, while the scour depth for streamline geometry was (3) cm because
it has a minimum exposed area without side corners, so scour rate and scour depth is
minimum as compared to others shapes.
NO. SHAPE
SHAPE
FACTOR
MEASURED
SCOUR DEPTH
(CM)
THEORETICAL VALUE (CM)
(CSU)
BREUSERS ET
AL.,1977
1 CIRCULAR 1 6.9 7.4 8.15
2 RECTANGULAR 1.11 7.6 8.2 9.05
3 OCTAGONAL - 5.7 - -
4 OBLONG 0.85 5.8 6.28 6.93
5 JOUKOWSKY 0.88 6.1 6.50 7.17
6 STREAMLINED 0.48 3 3.54 3.91
7 CHAMFERED 1.01 6.7 7.46 8.23
8 HEXAGONAL - 4.1 - -
9 ELLIPTICAL 0.8 5.6 5.91 6.52
10 SHARP NOSE 0.7 4.9 5.17 5.70

 The measured scour depth of pier models in this study agreed well with the calculated
scour depth from theoretical equations (Colorado state university and Breusers et al,
1977).
 The streamline shape is considered the best shape of piers that reduces the maximum
scour depth by 60% as compared with rectangular shape.
 It seen that, the scour depth increases as the flow intensity increases and vice versa.
REFERENCES
[1] Arneson, L.A., Zevenbergen, L.W., Lagasse, P.F., and Clopper, P.E., 2012,
Evaluating scour at bridges – Fifth Edition, Federal Highway Administration
Hydraulic Engineering Circular No. 18, FHWA-HIF-12-003, FHWA,
Washington, DC.
[2] Breusers, H., Nicollet, G., and Shen, H., 1977, Local scour around cylindrical
piers, Journal of Hydraulic Research, IAHR, 15 (3): 211-252.
[3] Chiew, W.M. (1984), Local Scour at Bridge Piers, School of Engineering, New
Zealand, phd. Thesis, Dept. of Civil eng., Report No. 355.
[4] Chiew, Y. M. and Melville, B. M., 1987, Local scour around bridge piers, J.
Hydraul. Res., 25(1), 15-26.
[5] Hamil L., 2000, Bridge Hydraulics, Taylor & Francis Taylor e-Library.
[6] Jueyi sui, Hossein, A, Abdolreza, K, Samani, and Mehrnoosh, M, 2010, Clear-
water scour around semi-elliptical abutments with armored beds, International
Journal of Sediment Research 25 - 233-245.
[7] Melville, B.W. and Coleman, S.E., 2000, Bridge scour, Water Resources
Publications, LLC, Colorado, U.S.A.
[8] Melville, B.W., 1997, Pier and Abutment Scour: Integrated Approach, Journal of
Hydraulic Engineering, ASCE, 123(2), February, 1997, pp.125-136.
[9] Adnan Ismael, Mustafa Gunal and Hamid Hussein, Use of Downstream-Facing
Aerofoil-Shaped Bridge Piers To Reduce Local Scour, International Journal of
Civil Engineering and Technology, 5(11), 2014, pp. 44-56.
[10] Dr. Avinash S. Joshi Dr. Namdeo A.Hedaoo Dr. Laxmikant M. Gupta, Transient
Elasto-Plastic Response of Bridge Piers Subjected To Vehicle Collision,
International Journal of Civil Engineering and Technology, 6(9), 2015, pp. 189-
204.
[11] Prof. P.T. Nimbalkar and Mr.Vipin Chandra, Estimation of Bridge Pier Scour for
Clear Water & Live bed Scour Condition, International Journal of Civil
Engineering and Technology, 4(3), 2013, pp. 92-97.

EXPERIMENTAL STUDY OF BRIDGE PIER SHAPE TO MINIMIZE LOCAL SCOUR

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