Use of Plastic Diaphragms to Improve the Resistance of River Embankments Against Hydraulic Failures

Failure of (floodplain) river embankments is mainly due to internal erosion phenomena, hydraulic heave, mechanical instability triggered by seepage forces. In order to minimize the risk of internal erosion (piping) or hydraulic heave, the use of plastic diaphragm or sheet piles is recommended. The main advantage of sheet piles is the structural resistance of this type of barrier which contributes to the mechanical resistance of the embankment and provides a hydraulic barrier even in the case that overtopping of the embankment has caused the erosion of the bank itself on the country side. On the other hand, sheet piles are very expensive and subject to possible corrosion or thickness reduction because of aggressive water and parasite currents into the soil. Plastic diaphragms are less expensive than sheet piles and can be installed quickly without compromising the serviceability of the embankment. This last advantage is also typical of sheet piles. The (dry) deep - mixing technology for the construction of plastic diaphragms is shortly illustrated and the advantages of such a method are pointed out. Eventually the effectiveness of a trial diaphragm, that have been constructed inside an existing (floodplain) river embankment at the Bottacci site (Province of Lucca, Northern Tuscany, Italy), is shown after the occurrence of repeated floods. Direct controls of the diaphragm and the information obtained by a monitoring system installed inside the embankment have been used for such a purpose. The geotechnical characterization of the embankment and of the monitoring system is illustrated in a companion paper.