Hydrological modeling in swelling/shrinking peat soils
M. Camporese, P. Salandin
Department of Hydraulic, Maritime, Environmental and Geotechnical
Engineering, University of Padova, Padova, Italy
S. Ferraris
Department of Agricultural, Forestry and Environmental Economics
and Engineering, University of Turin, Grugliasco, Italy
M. Putti, P. Teatini
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
ABSTRACT
Peatlands respond to natural hydrologic cycles of precipitation and
evapotranspiration with reversible deformations due to variations of water
content in both the unsaturated and saturated zone. This phenomenon results in
short-term vertical displacements of the soil surface that superimpose to the
irreversible long-term subsidence naturally occurring
in drained cropped peatlands because of bio-oxidation of the organic matter.
These processes cause changes in the peat structure, in particular, soil
density and void ratio. The consequential changes in the hydrological
parameters need to be incorporated in water flow dynamical models. In this
paper, we present a new constitutive relationship for the
soil shrinkage characteristic (SSC) in peats by describing the variation of
porosity with moisture content. This model, based on simple physical
considerations, is valid for both anisotropic and isotropic three-dimensional
peat deformations. The capability of the proposed SSC to accurately describe
the deformation dynamics has been assessed by
comparison against a set of laboratory experimental results recently published.
The constitutive relationship has been implemented into a Richards's
equation-based numerical code and applied for the simulation of the peat soil
dynamics as observed in a peatland south of the Venice Lagoon, Italy, in an ad
hoc field experiment where the relevant parameters are continuously measured.
The modeling results match well a large set of field data encompassing a period
of more than 50 days and demonstrate that the
proposed approach allows for a reliable reproduction of the soil vertical
displacement dynamics as well as the hydrological behavior in terms of, for
example, water flow, moisture content, and suction.
