Effect of smear zone on the consolidation and strength characteristics of soil under radial drainage

Vertical drains installed in soft clay deposits enhance the rate of consolidation in preloading projects. Using a mandrel to install the prefabricated vertical drains (PVD), its insertion and withdrawal will result in the remoulding of the soil zone surrounding it, called the smear zone. The extent of the smear zone is an important parameter that characterizes the smearing effect. This paper describes this effect in terms of smear ratio (i.e., the ratio of the diameter of smear zone ds to the diameter of drain, dw) on the consolidation characteristics of soil with radial drainage. A series of radial consolidation tests with a predetermined smear zone in a model unit cell was conducted by varying the diameter of the smear zone. The experimental results show that beyond a smear ratio of 4, the soil behaves as if it is in a fully remoulded condition. The results were compared with some of the theoretical approaches reported in the literature. The analytical solution that predicts the time-settlement curve in a better way is identified. Also, it is observed that the gain in undrained shear strength due to the consolidation of soft clay decreases with the increase in the diameter of the smear.