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.

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