Confronto di procedure per la determinazione del limite di ritiro su terreni argillosi umbri

The shrinkage limit of a clayey soil is the water content at which the transition between semi-solid and solid states occurs. It is used in geotechnical studies for investigating hydraulic parameters, soil compressibility, and the settlement of buildings, embankments and dams, when the footing soil undergoes uniform or differential volume changes associated with shrinkage and swelling processes, acting for short and long periods. The two procedures most commonly used in geotechnical practice to determine the shrinkage limit are the analysis with mercury and with the wax. This work contributes to the knowledge of the differences between the results of these two test methods, and promotes the use of the wax procedure as the more suitable test, in terms of time consuming, test performance, computations, influence of laboratory conditions, manual skills of the operator, and of different test stages. This last topic was particularly investigated for the wax method, since some stages of this standardized procedure are not completely specified. This study also proposes a relationship between shrinkage limits determined by the two procedures, which can be confidently used to correlate shrinkage limit values obtained from the two test methods.