Numerical modeling of natural
land subsidence over sedimentary basins undergoing large compaction
G. Gambolati, G. Giunta, P. Teatini
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
ABSTRACT
The natural compaction driven by unsteady groundwater flow in an
accreting isothermal sedimentary basin is investigated by a new
numerical compaction model.
We assume a process of continuous vertical sedimentation and make use of a
1-D model of flow where water flow obeys relative Darcy's law in a
porous medium which undergoes a progressive compaction under the effect
of an increasing load of the overburden.
The time interval spanned by the simulation can be millions of years and soil
porosity, permeability and compressibility may vary with the effective
intergranular
stress according to empirically based constitutive relationships.
The model takes correctly into account the geometric non-linearity
which arises from the
consideration of large solid grain movement and is solved using both
the Eulerian
and the Lagrangian approach. It is shown that the Eulerian derivative
of the total vertical stress is well approximated by the sediment
loading rate, thus allowing for the removal of a heavy source of
non-linearity in the governing equations with a significant
acceleration of the iterative solution procedure.
Preliminary results from the non linear model are
compared with those of the linear model
of Bredehoeft and Hanshaw [1968] which neglects the medium compaction. These results
indicate that the geometric non-linearity is important in relatively
compressible and permeable basins, i.e. in basins which display a
significant deformation and are normally or almost normally
consolidated.
