Pore water pressure measurements as indicator or precursor of core hydraulic alteration in zoned Earth dams

Abstract In zoned earth dams, hydraulic properties that depart from design assumptions (hydraulic alteration) may be induced by erosion phenomena and affect the dam’s watertightness. This study investigates how pore water pressure observations support leakages in indicating or preceding core hydraulic alteration and the role of other monitored quantities in detecting the presence of fractures. For this purpose, the paper draws the main pore water pressure patterns that may accompany different scenarios of hydraulic alteration. The presented interpretative criteria for pore water pressures are applied to five case histories, four borrowed from the literature and one presented in this paper. They were selected because, for each of them, the presence of hydraulic alteration is somehow informed by pore-water pressure measurements in one or more zones of the dam body, such as the upstream shell, downstream shell, and core. Pore water pressures in the core are interpreted by referring to two local indicators. The first aims to identify measured pore water pressure distribution patterns consistent with fractured zones. The second uses stresses derived from the back-analysis of observations to pinpoint zones susceptible to hydraulic fracturing, according to the Sherard approach. An analysis of an Italian earth dam showcases how to represent these indicators to recognise the formation and evolution of fractures in the core.