Comparative Study of Riprap Model Design for Scour Protection of

Bridge Pier

Cut Talitha Salsabila Nuraprili

, Robby Yussac Tallar

and Alexander Yovan Suwono

Civil Engineering Department, Maranatha Christian University, Jl. Surya Sumantri.65, Bandung, Jawa Barat Indonesia

Keywords: Comparative Study, Local Scouring Riprap, Model Design.

Abstract: Streams have an important function for human by providing irrigation, electricity, etc. Streams also have the

sediments within that typically flow following the direction of water velocity. The differences in

characteristics among streams have also been clear since it can be changed easily due to climate change, or

other natural factors. Streams also can change in dimension according to the surrounded environmental

conditions, for example local scouring caused by bridge pier. And then by using riprap is the most common

countermeasure to prevent local scouring. Riprap is a method that can be used to prevent erosion in streams

or other conditions that have water flows with high velocity. Therefore, the purpose of this study is to compare

two models riprap design around the pier for scour protection. The riprap models that were compared are

rectangular and circle shaped. The condition used in this study is clear water condition, under sediment-based

layer design, and riprap layer thickness. The experimental study was used to compare both riprap model

design. The result of this study indicates that circle shape model riprap is better than a rectangular shape.

Further studies are necessary regarding the effect of flow type, cross-sectional shape, or other related

variables.

1 INTRODUCTION

Streams are one of the sources of water on this earth

and have an important function for humankind, it has

various characteristics and many models. For streams

flows, especially in urban areas, these streams have

bridged that function to connect roads separated by

streams(Tallar & Suen, 2017).

Bridge has more than one pier which functions as

a load-bearing from the bridge itself and other loads

such as live loads and dead loads. However, presence

of a pier, the type of flow of water will be changed

from horizontal to vertical, (Hao, 1993) so that local

scouring occurs around the pier and will result in the

lifting of the base of material around the pier and

resulting in damage to the foundation on the bridge

pier.

Since the bridge piers that damaged due to the

scouring, then require to prevent or control bridge

pier local scouring. Riprap is one of the solutions for

local scouring (Figure 1). Riprap is one of the

https://orcid.org/0000-0002-5641-5796

https://orcid.org/0000-0001-7307-3348

https://orcid.org/0000-0002-2577-8519

Figure 1: Local scouring around the pier (From:

Bintangtimur.net).

methods used for preventing local scouring (Rashno,

Zarrati, & Tabarestani, 2020). The material of riprap

is rocks arranged around the pier (Figure 2). With

used riprap around the pier, then it can reduce down

flow jet on bottom sediments against local scouring.

This study has been conducted, these studies

generally inspect the design of riprap size in clear

water scour conditions, for example Chiew (1995).

176

Nuraprili, C., Tallar, R. and Suwono, A.

Comparative Study of Riprap Model Design for Scour Protection of Bridge Pier.

DOI: 10.5220/0010747600003113

In Proceedings of the 1st International Conference on Emerging Issues in Technology, Engineering and Science (ICE-TES 2021), pages 176-179

ISBN: 978-989-758-601-9

A riprap modeling experiment will be carried out

in this study. The study aims to compare the two

riprap models that are rectangular and circular. The

positioned of two models riprap is around the pier to

prevent the impact of local scouring. This

experimental study aims to compare both models and

the results will show that the circular shape is better

than the rectangular.(Unger & Hager, 2006)

Figure 2: Example of riprap around the pier (From:

istiarto.staff.ugm.ac.id).

2 METHODS

To find a better riprap model, then this study will

show it. By using a comparative of the two models

that rectangular and circular shapes, using the same

amount of two discharge. Is supposed to take both Q

and Q

to make sure. Besides, another parameter that

would be used in this study, likes the size of the

gravels that would use in the riprap model design,

which would be used in the same size for both

models. (Khademghaeinya, Abrishami, Zarrati,

Karimaei Tabarestani, & Mashahir, 2020)

2.1 Sieve Analysis

Sieve analysis was used in this study to find out these

gravels size for riprap model design. By using many

different sizes of sieve, likes 19,1 mm or until 0,075

mm (Table 1). So, this analysis is important, to ensure

each layer of riprap is the same size as previously

determined.

2.2 Discharge Curve Analysis

To find out which discharge can restrain the flow that

exists in the streams, it can experiment with using a

discharge curve to find to get the best 2 results of

discharge or Q. At the time when did the experiment

with discharge curve analysis, try multiple discharges

25% discharge (Q

)

50 % discharge (Q

), and 75%

discharge (Q

2.3 Scenario Riprap Model Design

The riprap models that were compared in this study

are rectangular and circular. Riprap placed under

sediment-base layer design. The thickness of these

two riprap models is 30 mm and the dimension will

be used in 28 cm or 280 mm (diameter for circular

shape and length for rectangular shape) and the

diameter of the pier used in this study is 8 cm. In this

study, the condition of the water is on clear water

scour, it usually happens when low flow discharge.

This experimental study was used to compare two

models design to knows which models better to

prevent local scouring around the pier.

3 RESULT AND DISCUSSION

3.1 Sieve Analysis

Sieve analysis was an experiment in the laboratories,

to find out the gravel riprap size. Then dr

, from sieve

analysis data can be decided to gravel size to use in

riprap models design.

Table 1: Sieve Analysis.

No. Sieve

(inch)

Cumulative

Soil

Retained

(%)

Cumulative

Soil

Passing

(%)

19.1 mm (3/4”) 0 100

12.7 mm (1/2”) 81.871 18.129

9.52 mm (3/8”) 96.315 3.685

4.75 mm (No.4) 99.079 0.921

2.36 mm (No. 8) 99.089 0.911

1.18 mm (No.16) 99.119 0.881

0.6 mm (No. 30) 99.219 0.781

0.3 mm (No. 100) 99.274 0.726

0.15 mm (No. 100) 99.479 0.521

0.075 mm (No. 200) 99.750 0.250

PAN 100 0

By using the Aggregate Distribution Curve, dr

of the riprap gravels is 10,5 mm. These two riprap

models are used in this comparative study.

Comparative Study of Riprap Model Design for Scour Protection of Bridge Pier

177

Figure 3: Discharge curve analysis.

3.2 Discharge Curve Analysis Results

From the discharge values in Table 2, the results of

the discharge curve analysis are obtained. The curve

is depicted in Figure 3.

Table 2: Discharge Data.

Δh

Discharge (Q)

/s)

0.2169 0.0305

0.2124 0.0289

0.2026 0.0257

0.1941 0.0231

0.1886 0.0215

0.181 0.0194

0.1719 0.017

0.1631 0.0149

0.1569 0.0136

0.1459 0.0113

0.1394 0.0101

0.1292 0.0083

3.3 Scenario Riprap Model Design

The riprap models that were compared are circular

(Figure 4) and rectangular shaped (Figure 5). In this

study, the condition used is clear water condition,

under sediment-base layer design, and riprap layer

thickness. The riprap layer thickness used is 30 mm.

Figure 4: Illustration of riprap with circular shape (top view,

unit: mm).

Figure 5: Illustration of riprap with rectangular shape (top

view, unit: mm).

ICE-TES 2021 - International Conference on Emerging Issues in Technology, Engineering, and Science

178

4 CONCLUSIONS

The study shows that a riprap with a circular shape is

stronger than a rectangular shape. For 25% discharge,

the riprap with circular shape has 22% stronger than

a riprap with rectangular shape. For 50% discharge,

the riprap with circular shape has 28 % stronger than

a riprap with rectangular shape. For 75% discharge,

the riprap with circular shape has 33 % stronger than

a riprap with rectangular shape. Therefore, the

circular shape has presented about 20-35% stronger

with discharge under all discharge condition

compared to the rectangular shape.

The study also indicates that the riprap layer will

degrade to an equilibrium intensity below a given

constant discharge condition. Further studies are

necessary regarding the effect of flow type, the size

of bridge piers, such as the other shapes in which one

is stronger, and other related variables that can be

used in this study.

ACKNOWLEDGEMENTS

The author wishes to express their hearty thanks to

Civil Engineering Department, Maranatha Christian

University for the support and to LPPM (Lembaga

Penelitian & Pengabdian Masyarakat), Maranatha

Christian University.

REFERENCES

Hao, L. (1993). Hydraulic Computation for Riprap

Protection against Scouring around Bridge Piers [J].

Journal of Sediment Research, 3.

Khademghaeinya, G., Abrishami, J., Zarrati, A., Karimaei

Tabarestani, M., & Mashahir, M. (2020). Riprap design

at bridge piers with limited scouring. Scientia Iranica,

27(2), 588–595.

Rashno, E., Zarrati, A. R., & Tabarestani, M. K. (2020).

Design of riprap for bridge pier groups. Canadian

Journal of Civil Engineering, 47(5), 516–522.

Tallar, R. Y., & Suen, J.-P. (2017). Measuring the aesthetic

value of multifunctional lakes using an enhanced visual

quality method. Water, 9(4), 233.

Unger, J., & Hager, W. H. (2006). Riprap failure at circular

bridge piers. Journal of Hydraulic Engineering, 132(4),

354–362.

Comparative Study of Riprap Model Design for Scour Protection of Bridge Pier

179