Long-term performance of CSM walls in overconsolidated clays

The paper is concerned with the results of a comprehensive laboratory investigation carried out on soil samples drawn up from more than 50000 m2 panels realized using the Cutter Soil Mixing (CSM) for the construction of the new railway station in Bologna (Italy) where the subsoil is constituted mostly by overconsolidated clays. On the CSM-treated samples, hydraulic and mechanical laboratory tests at different curing time, from 14 days to more than 2 years, were performed, in order to study the influence of curing time on the overall mixture response and to propose a model aimed at describing the increase of mechanical properties along with time. The paper presents and discusses the outcome of the experimental investigation carried out so far, comparing the results obtained from preliminary tests on samples retrieved from trial panels with those obtained directly from the working structure. Furthermore, in order to understand the degree of mixture homogeneity reached by site mixing and the amount of cement effectively bonding the soil matrix, CSM-treated clayey soil was studied at micro-scale using microcomputed tomography.