Characterizing marshland compressibilityby an in-situ loading test: design and set-up
of an experiment in the Venice Lagoon
P. Teatini, P. Simonini, V. Girardi, P. Zorzan, C. Zoccarato, M. Ferronato, M. Marani, S. Cola
Dept. of Civil, Environmental and Architectural Engineering, University of Padova, Padova, Italy
C. Da Lio, A. Bergamasco, S. Pasqual, G. Zambon
Institute of Marine Sciences, CNR, Venice, Italy
L. Tosi
Institute of Geosciences and Earth Resources, CNR, Padova, Italy
M. Roner, A. D'Alpaos
Dept. of Geosciences, University of Padova, Padova, Italy
ABSTRACT
The fate of coastal marshlands in the near future will strongly depend on their
capability to maintain their elevation above a rising mean sea level. Together with the
deposition of inorganic sediments during high tides, organic soil production by
halophytic vegetation, and organic matter decomposition, land subsidence due to natural
soil compression is a major factor controlling the actual elevation of salt-marsh platforms.
Due to their high porosity and compressibility, the marsh sedimentary body undergoes large
compression because of the load of overlying more recent deposits. The characterization of
the geotechnical properties of these deposits is therefore of paramount importance to
quantify consolidation versus accretion and relative sea level rise. However, undisturbed
sampling of this loose material is extremely challenging and lab tests on in-situ collected
samples are not properly representative of in-situ conditions due to the scale effects in
highly heterogeneous silty soils such as those of the Venice lagoon. To overcome this
limitation, an in-situ loading test was carried out in the Lazzaretto Nuovo salt-marsh in
the Venice Lagoon, Italy. The load is obtained by a number of plastic tanks that are filled
with seawater, reaching a cumulative load of 40 kN applied on a 2.5x1.8 m2 surface.
Specific instrumentations were deployed before positioning the tanks to measure soil
vertical displacement at various depths below the load (0, 10, and 50 cm) and distances
(0, 40, and 80 cm) from the load centre. Moreover, six pressure transducers were used to
record overpressure dissipation over time. The collected datasets will be interpreted
through a 3-D flow-deformation model that, once calibrated, provides reliable estimates
of the compressibility values for each monitored depth interval.
