2024 – Considerations on Groundwater Flow through Embankment Dams and Piezometric Data Interpretation

Sonia Fortuna

The broad engineering industry has a core mandate to establish consistency. Engineers do this via creating and enforcing standards. However, no two dams being the same often calls for tailored solutions, where adopting a standardised approach becomes challenging, if not undesirable. The dams industry therefore faces a continuous tension, resolved by ad hoc use of judgement. Judgement is required in the design and review of piezometers plans, including the selection of piezometers location, tip elevation and screen size, aimed at capturing the key elements of the groundwater flow in and around the dam. Details that may appear inconsequential in the design of piezometers and in the interpretation of piezometric data without consideration of groundwater flow, may instead have an impact on the assessment of the integrity of the dam and follow on decisions. This paper discusses aspects of piezometric surveillance data typical of real Australian embankment dams, organised into three groundwater flow scenarios. Both theoretical (i.e. first principles) and practical aspects of groundwater flow in embankment dams are considered. Lessons learnt include how consideration of both practical details and theoretical aspects of groundwater flow in soils may turn some apparently odd piezometer’s behaviour – potentially leading to discounting an instrument – into reliable and valuable information about the performance and integrity of the structure. The paper shows how the overall level of understanding of the piezometric data may lead to substantially different paths: one of missing crucial information, or one of improved knowledge about the integrity of the dam which could inform the next steps being taken, from daily surveillance activity to future upgrades. The paper also illustrates how knowledge of geomechanics, geotechnical structures (foundations) design and soil-structure interaction concepts is crucial in understanding the surveillance data collected and the rational development of future instrumentation plans. Finally, following on from the latter point, the paper highlights the possible need for broadening the concept of failure mode in risk assessments, to include effects of long-term prefailure behaviour of dams – i.e. “pre-failure” modes.