Asphalt faced rockfill dams subjected to seismic loading
2022 - 2025
Asphalt concrete facings are a widely used sealing element for earth or rock fill dams of hydropower plant reservoirs in Switzerland and all over the world. During the strong Tohoku Earthquake in 2011 (Mw > 9.0), two Japanese asphalt faced rockfill dams were severely damaged. The facings of both dams lost their impermeability owing to cracks, which had formed during the strong seismic shaking. Only thanks to a rapid lowering of the water level, which had not been high during the earthquake anyways, severe water intrusion into the dam body and a potential erosion of the dams could be prevented.
In numerous research studies following this event, focusing also on other asphalt faced rockfill dams in Europe, this damage phenomenon could not be explained in a satisfactory way. These studies neglected important details regarding the response of the facing in a seismic event, namely the consideration of the interface between the dam and the facing, as well as the visco-elasto-plastic material behavior of the asphalt concrete. Furthermore, an assessment method concerning the structural health of the facing after a seismic event and the direct consequences regarding water leakage quantities has not been developed yet.
The goal of this research project is thus to investigate the behavior of asphalt faced rock fill dams under seismic loading in order to provide criteria for assessing the question, whether the facing is prone to lose its practical impermeability owing to earthquake action. It also addresses the issues mentioned before, based on data collected from two asphalt faced rock fill dams in Switzerland. Numerical models of these two dams are built up by applying state-of-the-art numerical modelling techniques. The analysis especially focuses on constitutive modeling of the asphalt facing by applying principles of rate dependent fracture mechanics. The fracture process is modelled using the extended finite element method (XFEM) and newly developed crack propagation criteria. The calibration of these fracture mechanical models requires highly specific and temperature dependent laboratory tests on asphalt samples from the two dams. The fracture mechanical models are integrated into the numerical dam models to analyze the system behavior by comprehensive parametric studies.
The methodology is verified by applying it to a numerical model of one of the Japanese dams that has been damaged during the Tohoku earthquake. The results serve as the basis for recommendations for engineering practice regarding the assessment of existing and newly constructed asphalt faced rock or earth fill dams.
Funding
Swiss Federal Office of Energy
Researcher
Tinet Ruch
Contact
Professur für Geotechnik
Stefano-Franscini-Platz 5
8093
Zürich
Switzerland