Three-dimensional creep analyses of the leaning tower of Pisa

Three-dimensional creep analyses are carried out to investigate the significance of soil creep effects on the tilting history of the Pisa Tower. Sensitivity analyses of model parameters are also conducted. Results show that three-dimensional creep analysis, although very time-consuming, is necessary in order to obtain more realistic numerical results. Creep effects have been found to account for 1.5 degrees out of the total 5.5 degrees inclination. Creep causes stress states in the clay layers to move away from the critical state line. It was also found that the deformation behaviour of the soil is not sensitive to any specific parameters. This helps to clarify that the total tilting angle of 5.5 degrees cannot be achieved by creeping of the soil. There must be other reasons that also contribute to the tilting of the tower, which cannot be considered by the constitutive model. Nevertheless, the current study could calculate the tilting history of the tower within reasonable accuracy during its construction period and illustrate more or less, the same trend as observed through the last four centuries. The model could also match the observed maximum settlement on top of the upper clay layers extremely well. Therefore, this study provides considerable insight into the deformation history of the soil and the stresses that are likely to exist in the soil.