CPT-based assessment of densification induced by stone column installation

Abstract

The use of CPTs for liquefaction susceptibility assessment has become increasingly common in design practice. In the past, the design of densification soil improvement methods against liquefaction has been commonly based on experience, large scale field tests and, possibly, validation after the intervention. Nevertheless, a design method to assess quantitatively the densification effect induced by stone column installation can be developed following a workflow based on CPTs, in order to estimate the efficiency of the soil improvement and to check the compliance with safety requirements before accessing the site. As by common practice, the assessment of liquefaction susceptibility is performed by means of CPT data and related empirical methods. The design method proposed in this paper is based on the estimation of modifications induced by the soil densification technique, easily detectable by the CPT profile, in order to carry out a liquefaction susceptibility analysis. The approach is applied in particular to a well-documented case study in Northern Italy (Bondeno, Ferrara province), providing a consistent dataset of piezocone tests carried out before and after soil treatment through stone columns, as part of a blast-induced liquefaction experiment. In this way, a clear comparison between pre- and post- intervention conditions along the CPT profiles with depth can be performed, thus allowing a validation of the design methodology.