Riprap design at bridge piers with limited scouring

Document Type : Article


1 Department of Civil Engineering, Ferdowsi University, Mashhad, Iran.

2 Department of Civil Engineering, Ferdowsi University, Mashhad, Iran

3 Department of Civil and Environmental Engineering, Amirkabir University of Technology, Tehran, P.O. Box 15915, Iran

4 Department of Civil Engineering, Shahid Rajaee Teacher Training University, Lavizan, Tehran, P.O. Box 16785-163, Iran


In previous studies, sizing riprap layer around bridge pier as scour countermeasure was for 100% protection against scouring. However, in many cases limited scour depth around a pier maybe accepted if only smaller riprap sizes are available. In the present work the effects of smaller size of riprap stones than the stable size on the scour depth is studied. Circular and oval shapes for riprap extent as well as both round and angular stone shape were tested. All tests were conducted at the threshold of bed sediment motion and the maximum scour depth was measured. The results of these experiments showed that with stone sizes closer to stable riprap, the efficiency of both round and angular stone shape was identical. As, size of riprap was reduced, deeper scour holes were observed with both round and angular shape material. The results also indicated that increasing the extent of the riprap layer from circular to oval with 5 times more riprap volume had insignificant effects on scour hole for angular shape riprap meanwhile reduced the scour depth with round shape material. Based on experimental data a method was developed to calculate a smaller riprap size based on an accepted limited scour hole.


1. Raudkivi, A., Loose Boundary Hydraulics, A.A.
Balkema, Rotterdam, Brook eld, Netherlands (1998).
2. Karimaei Tabarestani, M. and Zarrati, A.R. Local
scour calculation around bridge pier during
event", KSCE J. Civil Eng., 21(4), pp. 1462{1472
3. Zarrati, A.R., Nazariha, M., and Mashahir, M.B.
Reduction of local scour in the vicinity of bridge pier
groups using collars and riprap", J. Hydraul. Eng.,
132(2), pp. 154{162 (2006).
4. Karimaei Tabarestani, M. and Zarrati, A.R. E ect
of collar on time development and extent of scour
hole around cylindrical bridge piers", Int. J. Eng.,
Transactions C, 25(1), pp. 11{16 (2011).
5. Melville, B.W. and Had eld, A.C. Use of sacri cial
piles as pier scour countermeasures", J. Hydraul. Eng.,
125(11), pp. 1221{1224 (1999).
6. Chiew, Y.M. Scour protection at bridge piers", J.
Hydraul. Eng., 118(9), pp. 1260{1269 (1992).
7. Gaudio, R., Tafarojnoruz, A., and Calomino, F. Combined

ow-altering countermeasures against bridge
pier scour", J. Hydraul. Res., 50(1), pp. 35{43 (2012).
8. Tafarojnoruz, A., Gaudio, R., and Calomino, F. Evaluation
ow-altering countermeasures against bridge
pier scour", J. Hydraul. Eng., 138(3), pp. 297{305
9. Chiew, Y.M. Mechanics of riprap failure at bridge
pier", J. Hydraul. Eng., 121(9), pp. 635{643 (1995).
10. Richardson, E.V. and Davis, S.R. Evaluating scour
at bridges", Hydraul. Eng. Circular, No. 18 (HEC-18
Fourth Edition), FHWA NHI 01-001, Federal Highway
Administration, Washington, D.C. (2001).
11. Lagasse, P.F., Clopper, P.E., Zevenbergen, L.W.,
and Girard, L.G. Countermeasures to protect bridge
piers from scour", NCHRP Report 593, TRB, NAS,
Washington D.C. (2007).
12. Mashahir, M.B., Zarrati, A.R., and Mokallaf, E.
Application of riprap and collar to prevent scouring
around piers rectangular bridge", J. Hydraul. Eng.,
136(3), pp. 183{187 (2009).
13. Karimaei Tabarestani, M. and Zarrati, A.R. Design of
stable riprap around aligned and skewed rectangular
bridge piers", J. Hydraul. Eng., 139(8), pp. 911{916
14. Karimaei Tabarestani, M. and Zarrati, A.R. Design of
riprap stone around bridge piers using empirical and
neural network method", Civil Eng. Infrast. J., 48(1),
pp. 175{188 (2015a).
15. Karimaei Tabarestani, M., Zarrati, A.R., Mashahir,
M.B., and Mokallaf, E. Extent of riprap layer with
di erent stone sizes around rectangular bridge piers
with or without an attached collar", Scientia Iranica,
Trans. A, 22(3), pp. 709{716 (2015b).
16. Karimaei Tabarestani, M., Azarmidokht, H.R.,
Zarrati, A.R., and Anvary, S. Optimum design of
riprap extension with di erent stone size at rectangular
bridge piers with and without protective collar", I.
Hydraul. J., 10(4), pp. 51{64 (2016) (In Persian).
17. Froehlich, D.C. Protecting bridge piers with loose
rock riprap", J. App. Wat. Eng. & Res., 1(1), pp. 39{
57 (2013).
18. Chiew, Y.M. and Lim, F.H. Failure behavior of riprap
layer at bridge piers under live-bed condition", J.
Hydraul. Eng., 126(1), pp. 43{55 (2000).
19. Chiew, Y.M. Local scour and riprap stability at
bridge piers in a degrading channel", J. Hydraul. Eng.,
130(3), pp. 218{226 (2004).
20. Lauchlan, C.S. and Melville, B.W. Riprap protection
at bridge piers", J. Hydraul. Eng., 127(5), pp. 412{418
Gh. Khademghaeiny et al./Scientia Iranica, Transactions A: Civil Engineering 27 (2020) 588{595 595
21. Unger, J. and Hager, W.H. Riprap failure at circular
bridge piers", J. Hydraul. Eng., 132(4), pp. 354{362
22. Rajaratnam, N. and Nwachukwu, B.A. Erosion near
groynelike structures" J. Hydraul. Res., 21(4), pp.
277{287 (1983).
23. Oliveto, G. and Hager, W.H. Temporal evolution
of clear-water pier and abutment scour", J. Hydraul.
Eng., 128(9), pp. 811{820 (2002).
24. Garde, R.J. and Ranga Raju, K.G., Mechanics of Sediment
Transportation and Alluvial Stream Problems,
Wiley Eastern Limited, New Delhi (1977).
25. Raudkivi, A. and Ettema, R. E ect of sediment
gradation on clear water scour", J. Hydraul. Div.,
103(HY10), pp. 1209{1213 (1977).
26. Melville, B.W. and Sutherland, A.J. Design method
for local scour at bridge piers", J. Hydraul. Eng.,
114(10), pp. 1210{1226 (1988).