Effectiveness of Plastic Board Drains Installed in Soft Ground.

This study was conducted to evaluate the performance of plastic board drain (PBD) which is commonly used in a ground improvement technology to accelerate the consolidation of soft clayey soils. A series of discharge capacity tests in laboratory was performed using different types and geometries of PBD with different lateral pressures, hydraulic gradients, elapsed times, and deformation of drains. Cylindrical consolidation tests for the clay specimens with PBD were also conducted. In addition, finite differential analysis was performed for the comparison between the results from numerical analysis and those from the cylindrical consolidation tests. Four different types of drain samples were selected among drains generally used in the field. The results from this study can be summarized as follows: (1) For the measurement of accurate discharge capacity in laboratory, we recommend to use PBD surrounded by clayey soils. Moreover, continuous measurement of discharge capacity is required because the discharge capacity is highly dependent on the elapsed time. (2) The results from the cylindrical consolidation test and numerical analysis show that the consolidation velocity with drains is about five times faster than that without drains. (3) From the results of the parameter study, the effect of coefficient of vertical consolidation C_v on consolidation velocity was much higher than that of lateral consolidation C_h. In addition, the consolidation velocity is highly affected by the variation of smear zone rather than that of transition zone. (4) From the numerical analysis, it was shown that the degree of consolidation decreased considerably due to the development of both smear zone and transition zone resulting from soil disturbance during PBD installation.