Design and Execution of Vibro Stone Columns with Drainage and Reinforcing Functions

ABSTRACT: Stone columns are vertical elements made of coarse-grained materials installed in the ground to improve the load bearing behavior of the ground through their reinforcing function. Due to the relatively high permeability of the columns, they can also function as vertical drains and not only improve the seismic performance of the ground through faster dissipation of the earthquake-induced excess pore water pressure, but also accelerate the consolidation rate in fine-grained subsoil layers subjected to a surcharge load. In this paper a case study project is presented in which the ground consisted of a 7-m-thick very soft fine-grained layer. The ground was first treated by stone columns and then preloaded with a 7.5-m embankment. The main objective of this project was to increase the OCR and improve the modulus of deformation of the soft layers through consolidation prior to the main construction. During the course of the consolidation, settlement and piezometric pore water pressure at different points of the ground were recorded. The pore water pressure dissipation and the ground subsidence were calculated using Plaxis software. All material properties needed for the modelling were studied by various field and laboratory tests. There is reasonable match between the simulation results and the monitored data which validates the employed calculation approach and the selected material properties, with which the long term consolidation behavior of the stone-column-treated ground under the working load was predicted.