Description of failure mechanism in placed riprap on steep slope with unsupported toe using smartstone probes

Abstract

This article is aimed at investigating the influence of toe support conditions on stability aspects of placed ripraps on steep slopes exposed to overtopping flows. All past experimental model studies investigating placed riprap stability under overtopping conditions have been conducted with ripraps constrained at the toe section. However, ripraps constructed on the downstream slopes of rockfill dams are generally not provided with any form of toe support. Hence, it is of importance from stability and economical standpoints to understand the failure mechanism in placed ripraps with realistic toe support conditions. This article presents findings from experimental overtopping tests conducted on model placed ripraps unsupported at the toe section. Employing Smartstone probes, a new technology in stone movement monitoring, laser measurement techniques and Particle Image Velocimetry (PIV) techniques, detailed description of failure mechanism in placed ripraps under overtopping conditions is presented within this study. Study findings demonstrate sliding as the underlying failure mechanism in placed ripraps with unsupported toes. Further, comparison of experimental results with past findings revealed that placed ripraps with unrestrained toes experience a fivefold reduction in stability, characterized by the critical overtopping magnitude as compared with placed ripraps provided with fixed toe supports. Furthermore, toe support conditions were found to have no effects on either the failure mechanism nor the overall stability of dumped ripraps. Further research is recommended to arrive at well-defined methodologies for design and construction of toe supports for placed ripraps.