Overhanging failure is one of major problems in river engineering affected the riverbank geometry. Unfortunately, the previous analytical approaches had limitation on coupling fluvial erosion and overhanging block stability. Therefore, the aim of this paper is to introduce a new analytical approach for calculating the coupling fluvial erosion and overhanging failure of the experimental riverbanks and real riverbank ,the U-Tapao river, Songkhla Province, Thailand.
For fluvial erosion, the actual shear stress of the experimental riverbanks are between 2.98 and 5.67 Pa, while the U-Tapao river is determined as 12.03 Pa. Moreover, the critical shear stress of the experimental riverbanks are estimated in the range from 2.64 to 3.59 Pa, while the U-Tapao river is 11.73 Pa. Additionally, we found that the previous empirical erodibility coefficient equations cannot apply for this analytical approach because of different riverbank material properties, covered vegetation, and consolidation load on the riverbanks. For overhanging block stability, the factor of safety in beam-type failure are smaller than one in experimental riverbanks whereas the factor of safety in shear-type failure is smaller than one in the U-Tapao river. Furthermore, These overhanging failure types are consistent with the previous studies, as the shear-type and beam-type failure were reported as the dominant overhanging failure mechanism.
Finally, the overhanging failure mechanisms were simulated by numerical model within the framework of fluvial erosion and overhanging failure and the numerical results were validated with the temporal averaged bank width. This validation showed a good agreement between the numerical results and the experimental measurements.