Displacements as failure origin of placed riprap on steep slopes

ABSTRACT

This paper presents results from a scale model study related to the stability of dumped and placed riprap on steep slopes of 1:1.5 (vertical: horizontal) exposed to overtopping. The experiments showed that small rearrangements of the stones in placed riprap, quantified as displacements of particular stones, led to a compaction in the lower part of the riprap and to loosening in the upstream part. The riprap became unstable when the maximum displacements exceeded the size of the longest axes of the riprap stones. The experimental data were used to develop a relationship to describe the development of the displacements taking the load-history into account. The obtained results were indirectly confirmed by comparison with findings of two reports which are described in the present paper. Moreover, placing the riprap stones in an interlocking pattern resulted in five times higher critical discharges compared to randomly dumped riprap.

Keywords:

• Displacements
• erosion control
• flow-structure interactions
• hydraulic models
• interlocking pattern
• riprap stability

Acknowledgements

The authors thank the Master degree students Eirik Helgetun Pettersen, Jens Jakobsen and Fredrikke Kjosavik for their help in carrying out the physical model tests and the staff of the NTNU hydraulic laboratory for technical assistance. The permissions to use the reports of Larsen et al. (1986) and Sommer (1997) by the Regierungspräsidium Karlsruhe and the Karlsruhe Institute of Technology are acknowledged. The authors appreciated the comments of the editor and reviewers which helped to improve this article.

ORCID

Priska H. Hiller http://orcid.org/0000-0002-7639-5358

Jochen Aberle http://orcid.org/0000-0002-5435-2832

Additional information

Funding

The financial support of the collaborators within the project “Placed riprap on rockfill dams” (PlaF) coordinated by Energy Norway, and the Research Council of Norway [project no. 235730] is kindly acknowledged.