Experimental Study on Riprap Layer Design for Circular Bridge Pier
Efferiki
a
, Robby Yussac Tallar
b
and Alexander Yovan Suwono
c
Civil Engineering Department, Maranatha Christian University, Jl. Surya Sumantri 65, Bandung, Jawa Barat, Indonesia
Keywords: Circular Bride Pier, Riprap Layer Design, Local Scour.
Abstract: Scouring is a natural phenomenon that often occurs in streams. Scouring can also occur locally if there are
any changes in streams such as structural components within. A review of the literature has been accomplished
to investigate the previous results of the effectiveness of riprap design. However, few studies were focused
on the position of riprap layer design. Therefore, the main purpose of this study is to compare the effectiveness
of riprap layer design for circular bridge pier by experimental study. Several scenarios have been set up by
compared two layers conditions (the lower and upper sediment-based riprap layer design). The flow sediment
condition used in this research is clear water condition. The stable riprap size and the optimized extension of
the riprap layer around the circular pier along the flow direction were studied experimentally. The result
indicates that the lower sediment-based riprap layer design is ±10 to 20% more effective compared to the
upper sediment-based riprap layer design with different discharge flow scenarios. Further studies are also
needed regarding the effect of riprap characteristics such as shape and diameter, variations of riprap thickness,
and other related variables.
1 INTRODUCTION
Scouring is a natural phenomenon that often occurs in
streams (Mashahir, Zarrati, & Mokallaf, 2010;
Youssef, 2018). Scouring can also occur locally if
there are any changes in streams such as structural
components within (Tallar & Suen, 2015). Structural
components will block water flow that creates
horseshoe vortex system (Graf & Istiarto, 2002). This
horseshoe vortex causes water level drops and called
local scouring. Local scouring can be identified as an
abrupt decline in bed level due to erosion of bed
material by the local flow structure induced by
obstruction such as bridge pier set in the river (Figure
1).
Bridge is one of the most common structural
components built-in streams to connect two or more
places (Chiew & Lim, 2000). Local Scouring may
endanger the structural components of the bridge,
especially bridge piers. These days, there are so many
ways used to prevent local scouring. Riprap is a
common structure used to protect pier and abutment
of the bridge, stilling basin and other structures within
stream being vulnerable to deteriorative erosion
a
https://orcid.org/0000-0002-4408-6120
b
https://orcid.org/0000-0001-7307-3348
c
https://orcid.org/0000-0002-2577-8519
caused by flow velocity (Lagasse, 2006). Riprap
consists of stones that are installed in the bridge pier
base. The reason why riprap is still commonly used to
protect structural components, because it is easy to
repair the riprap, and riprap construction does not cost
much.
Figure 1: Local scouring at bridge pier.
A review of the literature has been accomplished
to investigate the previous results of the effectiveness
of riprap design (Tabarestani & Zarrati, 2013).
However, few studies were focused on the position of
riprap layer design. Some facts that happen in the
172
Efferiki, ., Tallar, R. and Suwono, A.
Experimental Study on Riprap Layer Design for Circular Bridge Pier.
DOI: 10.5220/0010747500003113
In Proceedings of the 1st International Conference on Emerging Issues in Technology, Engineering and Science (ICE-TES 2021), pages 172-175
ISBN: 978-989-758-601-9
Copyright
c
 2022 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved

field also show that riprap stones are carried away by
streams. Therefore, the main purpose of this study is
to compare the effectiveness of riprap layer design for
circular bridge pier. The scope of this experimental
study was performed in rectangular channel with
clear-water condition.
2 METHODS
To study the effectiveness of riprap layer design,
experimental research was carried out. This research
used average discharge (Q
50%
) and optimum
discharge (Q
75%
) to validate the results of this
research. The parameter used to study the
effectiveness of the riprap layer design was score
depth and the stability of the riprap. The open channel
was used in this research to determine the
effectiveness of the riprap layer design.
2.1 Method for Discharge Analysis
To change the discharge of this experimental
research, discharge rating curve was needed.
Discharge data are important to determine the
effectiveness of the riprap layer design modelled in
this research. Discharge rating curve was drawn to
determine Q
50%
and Q
75%
, which will be used in this
research.
2.2 Method for Sieve Analysis
Sieve analysis was carried out to find the stone size
of the riprap. the stone size of the riprap will be used
as the control variable, so it is important to ensure that
the stone size of every riprap used in this research is
the same size which is average diameter (Dr
50
). Sieve
analysis was carried out by using a defined sieve.
These sieves come with different opening size, to
determine the stone grading.
2.3 Scenarios of Riprap Model
The first condition of this research used average
discharge (Q
50%
). Two scenarios were set up to
determine the effectiveness of riprap layer design.
The upper layer design was used in the first scenario
and the lower layer design was used in the second
scenario (Figure 2, 3, and 4). The thickness of the
riprap layer, the size of the pier, the stone size of the
riprap used as the control variable. The diameter of
the pier used in this research is 8 cm and placed 120
cm from downstream of the weir. Based on previous
research, the thickness of the riprap layer used in this
research was 2,5 cm.
The riprap was installed circular around the pier
with a diameter of 28 cm. The second condition used
Q
75%
to validate the first case. The scenarios and the
control variable for the second condition were set up
similar to the first condition.
Figure 2: Side view of upper layer design.
Figure 3: Side view of lower layer design.
Figure 4: Top view of lower and upper layer design.
Experimental Study on Riprap Layer Design for Circular Bridge Pier
173

3 RESULTS AND DISCUSSION
3.1 Discharge Analysis Result
From the experiment in the laboratory, discharge
curve rating was drawn. After that, the Q
50%
and Q
75%
can be determined from the discharge curve rating
(Figure 5).
Figure 5: Discharge curve rating.
Based on the curve rating above, the value of Q
50%
=
0.0125 m
3
/s, and Q
75%
= 0.0188 m
3
/s
3.2 Sieve Analysis Result
From the sieve analysis experiment in the laboratory,
Dr
50
can be determined based on soil particle size
distribution (Figure 6).
Figure 6: Soil particle distribution.
Based on the soil particle distribution above, Dr
50
of
the riprap stone is 3.8 mm.
3.3 Riprap Model Result
After the discharge analysis and sieve analysis
experiment, we can continue the research with riprap
modelling. The effectiveness of riprap layer design is
determined by the depth of scouring. The depth of
scouring in the upper layer design was compared to
the depth of the scouring in the lower layer design.
The result of the first condition of the riprap model
using Q
50%
(Table 1):
Table 1: Result of the first condition of riprap model.
Scenario Thickness of
the riprap (mm)
Depth of
Scouring D
s
(mm)
Upper la
y
e
r
25 -11
Lowe
r
la
y
e
r
25 -9
𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒𝑛𝑒𝑠𝑠  
𝑑

𝑑

𝑑

 𝑥 100%
𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒𝑛𝑒𝑠  
11  9
11
 𝑥 100%
𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒𝑛𝑒𝑠  18.18 %
The result of the second condition of the riprap model
using Q
75%
(Table 2):
Table 2: Result of the second condition of riprap model.
Scenario Thickness of
the riprap
(mm)
Depth of
Scouring D
s
(mm)
Upper La
y
e
r
25 -21
Lowe
r
La
y
e
r
25 -18
𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒𝑛𝑒𝑠𝑠  
𝑑

𝑑

𝑑

 𝑥 100%
𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒𝑛𝑒𝑠  
21  18
21
 𝑥 100%
𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒𝑛𝑒𝑠  14.29 %
4 CONCLUSIONS
Based on the experiment, the result indicates that the
lower sediment-based riprap layer design is ±10 to
20% more effective compared to the upper sediment-
based riprap layer design with different discharge
flow conditions. With Q
50%
that was used in the first
condition shows that the lower sediment-based riprap
layer design is 18.18% more effective than the upper
sediment-based riprap layer design. In the second
condition, the lower sediment-based riprap layer
design is 14.29% more effective than the upper
sediment-based riprap layer design.
This research can be used to another structure
components beside piers along the stream. Further
studies are also needed regarding the effect of riprap
characteristics such as shape and diameter, variations
of riprap thickness, and other related variables.
0
20
40
60
80
100
120
0,1 1 10 100
PercentPassing(%)
Diameter(mm)
0
0,05
0,1
0,15
0,2
0,25
0 0,01 0,02 0,03 0,04
h(m)
Discharge(m
3
/s)
ICE-TES 2021 - International Conference on Emerging Issues in Technology, Engineering, and Science
174

ACKNOWLEDGEMENTS
The authors gratefully appreciate the support from
Civil Engineering Department, Maranatha Christian
University, Indonesia.
REFERENCES
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riprap layer at bridge piers under live-bed conditions.
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hole around a cylinder. Journal of Hydraulic Research,
40(1), 13–20.
Lagasse, P. F. (2006). Riprap design criteria, recommended
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Mashahir, M. B., Zarrati, A. R., & Mokallaf, E. (2010).
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Tabarestani, M. K., & Zarrati, A. R. (2013). Design of
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Youssef, I. H. (2018). A novel method for riprap design of
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