Numerical analysis for widening embankments over soft soils treated by PVD and DJM columns

The appropriate selection of treatment methods for a soft soil subgrade is critical to highway widening projects. In this paper, plane strain conditions are considered in the analysis of prefabricated vertical drains (PVD) and dry jet mixing (DJM) columns. PLAXIS is used to develop the finite element models for the simulation of PVD and DJM treated embankments over soft soils for highway widening projects. The model results include the settlements during and after embankment construction and the lateral displacements of the subgrade. This paper also investigates the working mechanisms when the two subgrade treatment methods are adopted for the widening of embankments over soft soils by analysing the excess pore water pressure distribution in the soft soils. In-situ embankment tests are used to validate the proposed numerical model. The results show that the conventional PVD method causes a soil arching effect in the old embankment and excessive ground disturbance during construction despite the fact that this method can reduce the post-construction soil settlement and the lateral displacement during construction. In comparison, the DJM treatment can greatly reduce the settlement during construction, the settlement and differential settlement after construction, and the lateral displacements. Finally, several techniques are summarised to improve the conventional PVD method, providing practical value for widening highway embankments over soft soils.