Back Analyses of PVD Performance in Mumbai Port

Abstract

This paper presents the instrumentation and back analyses conducted to assess the field performance of ground improvement works in one of the port development projects along Mumbai coast. Ground improvement using Prefabricated Vertical Drains (PVD) with Preloading in excess of 90 ha reclamation of land was carried out to improve the soft estuarine deposit below the seabed. The marine clay along the Mumbai coastline was found to be very soft with undrained shear strength less than 5–7 kPa at the top of the mud. Extensive geotechnical campaigns were carried out to comprehend the variations in the geotechnical properties of the clays. The PVD design was conducted based on various design parameters derived from the investigation data. As the coefficient of horizontal consolidation (ch) values were found to be crucial in the estimation of rate of consolidation over time, various radial consolidation and cone dissipation tests were carried out. The ch values from these tests were observed to be in the range of 1.8–5.2 m2/yr, which yielded the design value of around 3 m2/yr. Extensive instrumentation and monitoring were conducted using multilevel magnetic extensometers, settlement gauges and piezometers to back calculate the field ch values. The back calculated field ch values were in the range of 3.7–4.7 m2/yr with smear diameter ratio of 2.5 and smear permeability ratio around 3–4. The back analyses helped to apply suitable corrections in the design parameters in the field, thereby accounting for the parametric variations in the field and also effectively mitigating the geotechnical risks.