The Problem of the Hydraulic Characterisation of Flood Embankment and Its Foundation: An Approach Based on the Use of Piezometers (PAP014312)

Código

PAP014312

Autores

annarita pozzato

Tema

Urban Floods

Resumo

The Adige river, the second longest river in Italy, was rectified in the late 19th century by building embankments about seven meters high. The river embankments are generally made of coarse-grained well graded soils but locally may include layers of finer materials. Because the Adige River was a braided river, the soil profile of the embankment foundation along the embankment length is extremely variable. Characterisation of the hydraulic behaviour of the foundation soils, which is critical in the evaluation of the embankment stability, is therefore problematic for these peculiar soil deposits. The paper presents an approach to characterise the hydraulic response of the foundation soils via dual standpipe/cell piezometers. Three case studies were analysed where data were available from manual monitoring in 'open' standpipe piezometers and from automatic monitoring in 'piezopress' cell piezometers. Soils at two different locations having similar grain size distributions and geological setting, which would have been intuitively classified as the 'same' soil, were characterised hydraulically via permeability tests in open standpipe piezometers. These soils showed them to have different hydraulic conductivities up to 3 orders of magnitude. It follows that formulation of typical cross sections for homogenous geological profiles (i.e. based on soil types), which is a common practice in engineering assessment of embankment stability, can be highly misleading. A second aspect of great relevance in the hydraulic response of the embankment is the anisotropy in the hydraulic conductivity of the foundation soils. The paper shows that piezometers can also be used to derive the anisotropy ratio (vertical to horizontal hydraulic conductivity) via back analysis of the pore water pressure recorded by piezometers at different location in the embankment foundation.