Document Type : Research Paper

Abstract

Because it is not possible to recognize the mechanism of cantilever failure in field studies, this type of common failure in riverbanks is investigated in the laboratory. For this purpose, two samples of susceptible soil that forms an overhanging block in riverbanks are used for physical model tests to determine their physical, chemical and mechanical characteristics. Soil blocks of different densities were formed and then undermined by hand at specific depths over specific time increments and the stability of the overhanging block were assessed at each step. The results showed that, under these laboratory study conditions, the dominant failure mechanism is toppling. This finding is in accordance with the overhanging failure pattern in the Kordan Riverbanks. It was also found that the failure mechanism in cohesive soil is progressive and accompanied by tension crack development. In Loess material, the failure mechanism is momentary and no deformations in the upper part of the soil block are observed.

Keywords

Amiri-Tokaldany, E. 2002. A model of bank erosion and equilibrium bed topography in river bends. PhD Thesis. University of Southampton. UK.
Dapporto, S., Rinaldi, M., Casagli, N. and Vannocci, P. 2003. Mechanisms of riverbank failure along the Arno River, central Italy. Earth Surface Processes and Landforms. 28(12): 1303-1323.
Darby, S.E. and Thorne, C.R. 1996. Development and testing of riverbank-stability analysis. J. Hydraul. Eng. 122(8): 443-454.
Darby, S. E. and Thorne, C. R. 1997. Discussion of Development and testing of riverbank-stability analysis. J. Hydraul. Eng. 123(11): 1052-1053.
Darby, S. E., Gessler, D. and Thorne, C. R. 2000. Computer program for stability analysis of steep, cohesive riverbanks. Earth Surface Processes and Landforms. 25(2): 175-190.
Darby, S. E., Rinaldi, M. and Dapporto, S. 2007. Coupled simulations of fluvial erosion and mass wasting for cohesive river banks. J. Geophys. Res. 112(F03022): 1-15.
Li, S., Knappett, J. and Feng, X. 2009. Investigation of slope stability influenced by change of reservoir water level in three gorges of China. In: Liu, J., Zhang, H., Liu, X. (Eds). Flow in porous media: from phenomena to engineering and beyond conference. International Forum on Porous Flow and Applications. April. 24-26. Wuhan. China. 911-916.
Osman, A. M. and Thorne, C. R. 1988. Riverbank stability analysis. I: Theory. J. Hydraul. Eng. 114 (2): 134-150.
Rinaldi, M. and Darby, S. E. 2008. Advances in modelling river bank erosion process. In: Habersack, H., Piégay, H., Rinaldi, M. (Eds). Gravel-Bed Rivers 6: From Process Understanding to River Restoration. Series Development in Earth Surface Processes. Elsevier. The Netherland. 213-239. 
Samadi, A. 2007. Personal Communication with Prof. Colin Thorne. Dept. of Irrigation and Reclamation Engineering. Uni. Tehran. IRAN.
Samadi, A., Amiri-Tokaldany, E. and Darby, S. E. 2009. Identifying the effects of parameter uncertainty on the reliability of riverbank stability modeling. Geomorphol. 106, 219-230.
Samadi, A. 2011. Experimental, and Analytical Investigation of the Stability of Riverbanks against Cantilever Failure. PhD Thesis. Dept. Irrigation and Reclamation Engineering. Uni. Tehran. IRAN. (in Farsi)
Simon, A., Curini, A., Darby, S. E. and Langendoen, E. J. 1999. Streambank mechanics and the role of bank and near-bank processes in incised channels. In: Darby, S. E., Simon, A. (Eds). Incised River Channels: Processes, Forms, Engineering and Management. John Wiley and Sons. Ltd. Chichester. U.K. 123-152.
Taghavi, M., Dovoudi, M. H., Amiri-Tokaldany, E. and Darby, S. E. 2010. An analytical method to estimate failure plane angle and tension crack depth for use in riverbank stability analyses. Geomorphol. 123(1-2): 74-83.
Thorne, C. R. and Tovey, N. K. 1981. Stability of composite river banks. Earth Surface Processes and Landforms. 6, 469-484.
Thorne, C. R. 1982. Processes and mechanisms of river bank erosion. In: Hey, R. D., Bathurst, J. C., and Thorne, C. R. (Eds). Gravel Bed Rivers. John Wiley & Sons. Ltd. Chichester. U.K. 227-271.
Thorne, C. R. 1999. Bank processes and channel evolution in the incised rivers of North-Central Mississippi. In: Darby, S. E., Simon, A. (Eds). Incised River Channels: Processes, Forms, Engineering and Management, John Wiley & Sons. Ltd. Chichester. U.K. 97-121.
Van Eerdt, M. M. 1985. Salt marsh cliff stability in the Oosterschelde. Earth Surface Processes and Landforms. 10(2): 95-106.