CASE STUDIES OF STONE COLUMNS IMPROVEMENT IN SEISMIC AREAS
Soil improvement with stone columns is often implemented in seismic areas in particular as a countermeasure against liquefaction. The efficiency of stone columns can be explained by the compaction effect during their execution, by the reduction of the seismic stress on the soil, and by their draining effect as well. A historical evolution of the first realisations is presented, followed by an inventory of the observed performance of such systems in seismic conditions. Then, recent applications of stone columns combined with pile foundations are presented. Key-Words: seismic area, stone columns, liquefaction, case study, pile foundation.
DILATION OF GRANULAR PILES IN MITIGATING LIQUEFACTION OF SAND DEPOSITS
Liquefaction of loose saturated sands still remains a challenging task for geotechnical engineers. Amongst the various remedial measures available, the use of granular piles or stone columns is one of the most popular choices. The dilation of dense granular material achieves three important phenomena, viz. reinforcement, drainage and densification. The effect of dilation on reinforcing action of granular piles has been quantified earlier. In this paper, the dilation effect on drainage function of granular piles/gravel drains is studied by extending Seed and Booker model. It is shown that the effect for the ranges of parameters considered is marginal.
The dissipation of excess pore pressures in contractive vibro-columns at small strains
A laboratory investigation into the mechanisms contributing to the dissipation of excess pore pressures by vibro-replacement stone columns has been carried out. The paper examines the results of the laboratory programme by using a simplified version of the analytical approach proposed by Seed and Booker to describe the main mechanisms of pore pressure dissipation. Modifications to this analysis are proposed, in view of the laboratory results, to include aspects of liquefaction mitigation due to the rigidity of the columnar inclusion and the performance constraints caused by finite column permeability. Nous avons enqueete en laboratoire sur les mecanismes contribuant a la dissipation des pressions de pores excessives au moyen de colonnes de pierre placees par vibration. Cette etude examine les resultats du programme mene en laboratoire en utilisant une version simplifiee de la methode analytique proposee par Seed et Booker pour decrire les principaux mecanismes de dissipation de pression de pore. Au regard...