Backward Erosion Monitored by Spatial–Temporal Pore Pressure Changes during Field Experiments

This paper focuses on understanding the temporal behavior of backward erosion using measurements from densely spaced piezometers during large-scale field experiments in October 2009 and September 2012 at IJkdijk in the Netherlands. Observations and data originate from nearly continuous monitoring of pore-water pressure and visual observations of seepage and sand boils. In 2009, the test progressed to breach (release of reservoir), while in 2012 the test included a vertical geotextile in the foundation to mitigate backward erosion such that the embankment did not breach. Study of pore-water pressure provides indicators of backward erosion (also known as piping) detectable in instrument readings. Temporally and spatially dense pore-water pressure measurements detect two pore-water pressure transitions characteristic to the development of internal erosion, even in piezometers located away from the backward erosion activity. First, the backward erosion causes anomalous pressure decrease in piezometers, even under constant or increasing upstream water level. Later, measurements stabilize as backward erosion extends further upstream of the piezometers, as shown in the 2009 test. In the 2012 test, measurements did not stabilize and the embankment did not breach, likely because of the geotextile installed vertically in the foundation near the downstream toe. The transitions provide an indication of the temporal development and the spatial extent of backward erosion.