ABSTRACT: In this Paper, a back-analysis of the behaviour of an oil tank during a loading test is presented, and the results of the analysis are compared with the actual performance of the tank resulting from field measurements. The tank is founded on stiff cohesive soils and on a clayey backfill improved with soil-cement columns, obtained with the deep-mixing technique. The constitutive model used in the analysis is capable to reproduce the soil non-linearity and has been calibrated using in-situ measurement of the stiffness at small strains. The backfill improved with stabilised columns is regarded as an equivalent homogenous material, characterised by a non-linear stress-strain behaviour. A coupled consolidation analysis is carried out, that provides a satisfactory simulation of the observed time-settlement curve and of the overall field of displacements monitored during the loading test. A less satisfactory agreement is obtained between measured and computed values of pore water pressure. The effectiveness of the soil improvement scheme adopted is finally evaluated, comparing the back-analysed performance with the results of additional analyses, in which no treatment or a different geometry of treatment are hypothesised.

Key words: case history, cohesive soil, deep mixing soil stabilisation, non-linear, numerical analysis, oil tank, settlement, soil improvement (IGC: D6/E2/H1)