Rapid development and associated urbanisation have forced engineers to construct earth structures such as highway and railway embankments over soft clay deposits. Soft clays are geologically young sediments deposited all over marine areas, which possess very low bearing capacity and high compressibility. Any construction over these deposits without adequate stabilization will lead to unacceptable settlements and lateral movements that could adversely affect the stability of structures.Accelerated pre-consolidation by preloading and vertical drains is one of the earliest and most widely used techniques for improving soft soils. The installation of Prefabricated vertical drains (PVD) in soft clay soils causes disturbance in the soil around them. This disturbed zone is called a smear zone. The smearing in the soil affects the permeability and consolidation properties. It is important to consider the smear zone parameters in designing the ground improvement with PVDs as it significantly affects the rate of consolidation. According to the existing literature, wide range of smear zone extent and permeability ratio are proposed and there is no definite method to predict the smear zone extent precisely to be used by practicing engineers.
In this study, an attempt is made to determine the extent of smear zone caused by different rates of mandrel installation (100-500 mm/min) through laboratory model tests employing Digital Image Correlation (DIC) technique. This technique includes a camera, lighting, and control system that facilitates image capturing at a fast rate. In addition to measuring the smear zone, excess pore pressures were monitored at different radial distances, and undisturbed soil samples were collected at various distances for conducting oedometer tests.The results of the experimental analyses will be presented and the findings will be discussed in the seminar.