Laboratory and Finite-Element Investigation of Soil Disturbance Associated with the Installation of Mandrel-Driven Prefabricated Vertical Drains

Abstract

A series of large-scale laboratory experiments, along with numerical analyses, using the commercial finite-element software package, ABAQUS, were performed to investigate the installation of mandrel-driven prefabricated vertical drains (PVDs). The laboratory tests were conducted using a specially designed large-scale consolidometer and a novel mandrel-driving machine capable of working at installation rates in the range of usual practices. The finite-element simulations include coupled analyses with a large-strain formulation. Coulomb’s law of friction and the penalty method are incorporated into the numerical models. The variations of pore water pressure at different locations during installation of a PVD and withdrawal of the mandrel are presented. Good agreement is found between pore pressures measured in the laboratory and predicted numerically. Moreover, finite-element analyses reveal that when a mandrel is pushed into the soil deposit, the soil surrounding the mandrel moves radially and downwards. Laboratory tests for moisture content and the numerically predicted variations of plastic shear strain, normalized with the rigidity index of the soil, show that for a given type of soft soil subjected to a particular rate of mandrel installation, the size of the smear zone decreases as the in situ effective stresses increase. The finite-element model has been applied to a case history from the Second Bangkok International Airport in Thailand and proves that the model can be applied to field conditions.