Numerical Analysis of Consolidation of Soft Ground Improved by the DJM-PVD Combined Method

Dry Jet Mixed (DJM) columns and Prefabricated Vertical Drains (PVDs) have been combined to improve soft ground for the Huai-yan Highway in China. This method could make the mixing of DJM columns easier and more homogeneous since the drainage of water through pre-installed PVDs reduces the excess pore pressure induced by the installation of DJM columns. In addition, the strength of the improved ground can be further quickly increased when the embankment load is applied at the existence of the PVDs. A two-dimensional plane-strain numerical model was adopted to analyze the consolidation of the DJM-PVD improved ground under the embankment load. The DJM columns and the PVDs in the treated ground were simply converted to DJM walls and PVD walls to obtain an equivalent plane-strain model. For comparison purposes, the conventional PVD improved ground, the DJM improved ground, and the unimproved ground were also analyzed. The numerical results showed that the DJM-PVD improved ground consolidated the fastest among these four types of ground. The stress concentration on the columns allows excess pore-water pressure in the surrounding clay to dissipate more quickly than that in the PVD improved ground.