This paper presents the results of an extensive parametric study on single piles and pile groups embedded in a two-layer subsoil profile, and is aimed to evaluate kinematic bending moments developing during earthquakes. A quasi three-dimensional finite element program has been used to perform dynamic analyses in the time domain. Piles have been considered as elastic beams, while the soil has been modelled using a linear elastic constitutive model. The aims of the paper are: (i) to evaluate kinematic bending moments in single piles and pile groups with dynamic analyses in the time domain, in different subsoil conditions; (ii) to review some existing design methods; (iii) to propose a simplified analysis procedure to evaluate maximum kinematic bending moments between two subsequent soil layers. The results of the dynamic analyses have shown that some of the simplified approaches provided in published literature tend to be conservative and can predict bending moments at the soil-layer interface with adequate accuracy only within certain depths of the soil layer interface. On the basis of the obtained results, a modified criterion to evaluate the transient peak bending moments at interfaces between layers is proposed.

The paper describes a new system for testing unsaturated soils designed at the University of Naples Federico II. The system is modular and can be configured either as an oedometer or a triaxial cell. Triaxial specimens are 68 mm in diameter and 140 mm in height, and oedometer specimens have a diameter of 56 mm and a height of 20 mm. The suction control is based on the axis translation technique. Radial strains are determined by an accurate measurement of the difference in pressures between the water filling an inner cell coaxial to the sample and that filling a reference double-walled burette, submitted to the same pressure. The water content variations are determined by measuring the difference in pressure in two double-walled burettes, one of which being connected to the drainage circuit, the other one operating as a reference. The calibration of all the devices, as well as their precision and accuracy, is widely discussed in the paper. Finally, the results of tests performed on an unsaturated pyroclastic soil are presented in order to highlight the features of both apparatuses.