Riprap design at bridge piers with limited scouring

Document Type : Article


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

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

3 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 ood  event", KSCE J. Civil Eng., 21(4), pp. 1462{1472  (2017).  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  of ow-altering countermeasures against bridge  pier scour", J. Hydraul. Eng., 138(3), pp. 297{305  (2012).  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  (2013).  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  (2001).  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  (2006).  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).