Analysis of field performance of embankments on soft clay deposit with and without PVD-improvement

This paper presents a case history of the performance of two full-scale test embankments constructed on soft clay deposit in the eastern coastal region of China. One embankment was constructed on natural subsoil and the other was constructed on prefabricated vertical drain (PVD) improved subsoil. The thickness of the soft clay deposit without PVD-improvement was 19 m and with PVD-improved case was 23 m. The PVDs were installed to a depth of 19 m with spacing of 1.5 m in a triangular pattern. Field performance of the two embankments was analyzed using the finite element method. The following influential factors: (i) hydraulic conductivity of subsoil in field and (ii) discharge capacity of PVDs were investigated numerically. The back-analyzed results for the embankment on natural subsoil showed that the hydraulic conductivity ratio (Cf) of field to laboratory values is about 6. To analyse the PVD-improved subsoil, a simple approach using the equivalent vertical hydraulic conductivity of PVD-improved subsoil was employed. The analytical results show that PVDs increased the bulk vertical hydraulic conductivity of soft subsoil by about 30 times compared to the original non-treated subsoil. The discharge capacity of PVDs in this field case is 79-100 m3/a, which is consistent with the findings from laboratory tests and other reported values in literature.