3D Displacement and Axial Load of Placed Riprap Supported at the Toe: Use of Structure from Motion

Improving the knowledge of the failure mechanism of riprap exposed to overtopping is valuable to enhance the construction and reinforcement techniques of rockfill dam defense systems. In this research, four experimental overtopping tests were carried out on $1:10$ rockfill dam models with placed riprap protection layers supported at the toe. Axial reaction loads were measured and 3D models were built using the structure from motion technique to study the displacement of riprap stones exposed to overtopping. The importance of throughflow in the rockfill shoulder is brought to light by comparing these results with previous data from a placed riprap model built on a ramp without throughflow. The structure from motion technique demonstrates to be very effective and highlights the existence of a buckling phenomenon, along with the compaction of the riprap. The displacement data show that the compaction mechanism is more important (both horizontally and vertically) and appears at lower overtopping discharges for less packed placed riprap layer. Finally, similar trends for vertical and horizontal riprap displacements are demonstrated between the initial position and the last position before failure. Such information suggests that the critical discharge value is not as critical as the riprap displacement to predict dam failure under overtopping conditions.