Research study of the hydraulic behaviour of the Po River embankments

Abstract

To investigate the hydraulic behaviour of the fine-grained embankments along the mid-course of the Po River, research was carried out on a full-scale physical model, built on the floodplain along the existing embankment and forming a pond. The pond was filled to reproduce historical floods. The prototype was built according to recommendations formulated by the Po River Management Authority. The engineering properties of the foundation soils were investigated by in situ tests and complemented by some suction-controlled laboratory tests. Pore-water pressure was measured in the embankment and in its foundation before, during, and after the experimental reproduction of two floods that occurred in 1976 and 2000. Atmospheric variables were monitored at the prototype site. Monitoring data refer to 6 months of experimental activities. Pore-water pressure measurements were first presented and subsequently interpreted through an isothermal two-dimensional flow approach where boundary flow rates express the evolution of atmospheric variables. The distribution of the pore water provided by this interpretation was used for stability analyses of the prototype. Results from the experimental activities and their interpretation indicate that the river embankment remains extensively unsaturated during floods. Typical suction trends within the embankment, suction-associated soil strength, and the resulting slope stability safety factors are also shown

Microstructure analysis of laboratory and in-situ compacted silts

“…The analysis of the in situ undisturbed samples retrieved during the construction (here not reported) confirmed that soil construction of the embankment was performed in wet conditions [8], with water contents higher than the reference Proctor optimum. It is worth noting, however, that the data shown refer to samples retrieved from the embankment some years after its construction, thus the actual water content values are likely to be also influenced by wetting-drying cycles that the embankment itself underwent under service conditions.…”

“…Some of the tested samples have been retrieved from an experimental embankment, 'identical' to the real embankments used for river regimentation purposes, built in order to evaluate the evolution of suction caused by soil-atmosphere and simulated flooding in real earth structure [8] . The embankment was constructed using the same compaction techniques adopted for service embankments using a fine-grained soil of medium plasticity taken from the floodplain.…”

On the role of partially saturated soil strength in the stability analysis of a river embankment under steady-state and transient seepage conditions

“…The aim was to simulate a typical suction distribution in a wet period, characterized by rainfalls that tend to reduce the soil suction near the top surface by heavy water infiltration. This hypothesis has been considered admissible [10,11,12] also in absence of specific site measurements. It is worth noticing here how the actual initial distribution of pore water pressures is of vital importance, as it strongly affects the final results.…”

A microstructure-based elastoplastic model to describe the behaviour of a compacted clayey silt in isotropic and triaxial compression

“…Daily and seasonal cycles of relative humidity, associated to different sequences of rainy and dry days, can be relevant in continental climates (e.g. Calabresi et al 2013) and, because of global warming, such cycles are expected to become more severe in the future (Rouainia et al 2009). Increasing severity of suction oscillations over time, and the previous experimental evidence on softening in the material response, justify why the effects of drying-wetting cycles on the hydro-mechanical behaviour of compacted soils for earthworks deserve careful attention.…”