Finite element analysis of embankments on soft ground incorporating reinforcement and drains.

The objectives of the research were threefold. Firstly, to improve .the
numerical modelling capability for reinforced embankments constructed
over soft compressible soils containing vertical drains. Secondly, to
demonstrate the ability to model accurately such embankments. Finally, to
develop simplified procedures to be used in the design of embankments
over soft soils.
The modifications to the finite element program, CRISP, included the
incorporation of three additional elements: modelling the reinforcement, the
soil/reinforcement interface and the vertical drains. The facility to vary
permeability with stress level was also implemented. A technique for
modelling the consolidation of soil containing vertical drains in plane strain
finite element analyses was developed and validated.
The modified program was validated in three ways. Firstly, each element
was used to analyse simple problems so that the correct formulation was
ensured. Secondly, a series of analyses was carried out of problems for
which analytical solutions were available; these problems involved collapse
of undrained sub soils and consolidation around a single vertical drain.
Thirdly, an analysis of a case history of an embankment constructed over a
normally consolidated clay, improved with vertical drains, was performed.
Based on the results of the previous finite element analyses, and an
additional analysis of an idealized two-stage constructed embankment,
simple design procedures have been proposed. Firstly, a method for the
design of single stage embankments and, secondly, a method for the
calculation of subsoil strength increases in multi-stage construction, which
can be used in conjucntion with limit equilibrium analyses.
It is concluded that the finite element method is a useful technique for the
analysis of reinforced embankments over soft soils containing vertical
drains.