An experimental investigation of the mechanical behaviour of a pyroclastic soft rock

This paper presents the results of an experimental investigation of the mechanical behaviour of a pyroclastic soft rock, locally known as Pozzolana Nera, from the volcanic complex of the Colli Albani (Roma). The laboratory testing programme consisted of standard drained and undrained triaxial compression tests, at increasing values of cell pressure. One-dimensional compression tests were also carried out in oedometers with reduced cross-section. The testing programme made it possible to investigate the full range of behaviour of the material from contractant to dilatant. Attention was focused on assessing the influence of natural microstructure on the shear strength parameters. The stress-dilatancy curves in triaxial compression were examined in an attempt to isolate the dilatancy component and the bonding component of peak strength.