The John Mitchell Lecture 2022: thinking conceptually about groundwater problems

Many excavations and tunnels experience problems and instability caused by uncontrolled groundwater inflows or groundwater pressures that influence stability and soil behaviour. A range of groundwater control measures can be used to overcome these problems and create stable and workably dry conditions below groundwater level. A key challenge for designers is that the performance of the various different techniques is strongly influenced by the hydrogeological conditions at a site. Furthermore, the available ground investigation data may have data gaps or considerable uncertainty regarding key parameters such as hydraulic conductivity or hydraulic boundary conditions. This means that, when working with real-world datasets, there are some groundwater problems where analysis involves so many assumptions and uncertainties that the design outcomes are of little practical value. This paper will discuss how thinking conceptually about groundwater problems can be of great benefit when developing groundwater control schemes, and propose that a robust conceptual model helps reduce the risk of designs being developed using inappropriate techniques. Historic examples from the nineteenth century and early twentieth century (before sophisticated methods of groundwater analysis were available) are described, where developing a conceptual understanding of groundwater conditions was vital in developing practical engineering solutions.