From Theory to Field Evidence: Observations on the Evolution of the Settlements of an Earthfill Dam, over Long Time Scales

Abstract

Unprecedented flooding events put dams and downstream communities at risk, as evidenced by the recent cases of the Oroville and Whaley bridge dams. Empirical models may describe expected ‘normal’ dam behaviour, but they do not account for changes due to recurring extreme weather events. Numerical modelling provides insights into this, but results are affected by the chosen material properties. Long-term field monitoring data can help with understanding the mechanical behaviour of earthfill dams and how this is affected by the environment over decades. We analyse the recorded settlements for one of the largest earthfill dams in Europe. We compare the evolution of these settlements to the reservoir level, rainfall, and the occurrence of earthquakes for a period of 31 years after first impoundment. We find that the clay core responds to the reservoir fluctuations with an increasing (from 0 to 6 months) time delay. This is the first time that a change in the behaviour of a central clay core dam, as observed from field data, is reported in the international literature. Seepage rates, as recorded within the drainage galleries, are directly affected by cumulative rainfall depths exceeding 67 mm per fortnight.

Subsurface condition assessment of critical dam infrastructure with non-invasive geophysical sensing

“…The cascading effects of dam failures to other infrastructure systems also indicate the urgent need for a proactive approach to manage and mitigate natural but also human threats to infrastructure systems 2020). The main reasons behind the current state of infrastructure lie (Pytharouli et al, 2019): (a) in the increasing age of these dams, (b) the current extreme climatic variability which is expected to cause major implications to structures as it has not been considered during their design phase and (c) that the existing models and prediction capabilities are not considered to be at advanced stage to reliable describe the long-term behavior of dams.…”

“…Despite that dams are currently considered to be the most well-instrumented structures (Pytharouli et al, 2019) in many occasions major deterioration processes that occur inside their body are not reliably detected by conventional instrumentation, which increases risk of failure (Michalis et al, 2016b). This is considered a major issue for key hazards such as internal erosion and seepage mechanisms which are caused by the hydrostatic pressure induced by increased water level of the reservoir and by desiccation due to the high permeability of the soil allowing water to infiltrate inside the body of the dam.…”

“…The geotechnical instrumentation can provide an important insight of the hazards occurring inside the body of dams, however, the vast majority of these instruments are not delivering reliable data in the long-term. This is due to the fact that they are difficult to be accessed after construction due to their internal installation inside the body of dams and as a result cannot be maintained properly (Pytharouli et al, 2019). During the dam operation, major deformations also occur inside their body which has a prominent damaging effect on these installed instruments.…”

“…The vast majority of the existing studies therefore focus on the deformations of dams analysing geodetic measurements (Dascal, 1987;Gikas and Sakellariou, 2008;Pytharouli and Stiros, 2009;Dounias et al, 2012;Michalis et al, 2016a;Gamse and Oberguggenberger, 2017;Scaioni et al, 2018;Zanganehasadabadi et al, 2019;Pytharouli et al, 2019). Studies based on the analysis of geodetic deformations have delivered key information about geometry changes of the body of the dam.…”

Advances in Dam Engineering

“…On the other hand, the numerical models provide insights into this, but results are affected by the chosen material properties. In the paper by Pytharouli et al [48] "From Theory to Field Evidence: Observations on the Evolution of the Settlements of an Earthfill Dam, over Long Time Scales," the authors analyzed the recorded settlements for one of the largest earthfill dams in Europe. They compared the evolution of the settlements to the reservoir level, rainfall, and the occurrence of earthquakes for over 31 years.…”