There are increasing demands from dam safety regulations and guidelines to upgrade the rockfill dams, especially in Norway where over 180 large rockfill dams are present. To protect the hydraulic structure against overtopping events or leakages, it is important to use defence mechanisms such as a protective layer of riprap on the downstream slope. In this article, we display 9 experimental setups of riprap, conducted at the hydraulic laboratory of NTNU (Trondheim) and subjected to overtopping phenomena with increasing water discharge, until the complete failure of the model. These tests were performed on models with dumped and placed riprap, with or without toe support, with or without the downstream rockfill shoulder, and finally on models with a full dam profile. The models with downstream rockfill shoulder as well as with full dam profiles allowed for throughflow. The model behaviour during these experimental tests is described and discussed, according to their respective critical discharge values and associated failure mechanisms. Limitations are also discussed. The results bring to light the benefit of placed riprap compared to dumped riprap structures. As the results show a placed riprap can withstand a significantly higher overtopping discharge than a dumped riprap. Also, the use of toe support enables a significant increase of resistance against overtopping of placed riprap structures. However, toe supports have not proven any significant improvement in stability for dumped riprap structures. This research also puts forward that dumped riprap undergoes a surface erosion process with smaller slides. Placed riprap undergoes a sliding failure mechanism when unsupported at the toe, and a buckling deformation when supported.

Rockfill dams must be equipped with defence mechanisms to counteract the destabilizing effects of throughflow forces under accidental leakage scenarios. A key component of the rockfill dam overtopping system is the rockfill dam toe, constructed in tandem with the downstream rockfill shoulder. Quantitative descriptions of effects of different toe configurations on throughflow hydraulic properties of rockfill dams are currently unavailable in international literature. To address this, experimental investigations were conducted on 1 m high model rockfill dams with disparate toe configurations. Investigation outcomes describe the effects of internal, external and combined toe configurations on pore-pressure distributions within rockfill dam models subjected to throughflow conditions. Research outcomes provide vital information which can facilitate effective decision-making with regards to rockfill dam design. The accumulated data sets could also enable development, calibration and validation of numerical design tools and dam breach models.

Dam failures are examples of man-made disasters that have stimulated investigation into the processes related to the failure of different dam types. Embankment dam breaching during an overtopping event is one of the major modes of failure for this dam type, comprising both earthfill and rockfill dams. This paper presents the results of a series of laboratory tests on breach initiation and progression in rockfill dams. Especially eight breaching tests of 1 m-high 1:10 scale embankment dams constructed of scaled well-graded rockfill were conducted. Tests were performed with and without an impervious core and under different inflow discharges. Controlling instrumentation includes up to nine video cameras used for image analysis and photogrammetry. A previously little-used technique of dynamic 3D photogrammetry has been applied to prepare 3D models every 5 s throughout the breaching process, allowing us to track in detail breach development. These dynamic 3D models along with pressure sensor data, flow data, and side-view video are used to provide data on erosion rates throughout the breaching process. One important purpose of this research is to test methods of observing a rapidly changing morphology such as an embankment dam breach that can easily be scaled up to large-scale and prototype-scale tests. The resulting data sets are further intended for the verification of existing empirical and numerical models for slope stability and breach development as well as the development of new models.