A study of pore properties in reconstituted Lucera clay at states of the critical state framework

Carefully designed oedometer and triaxial tests were carried out on reconstituted illite–smectite rich Lucera clay to reach specific states of the critical state soil mechanics (CSSM) framework, which were then investigated at the microscale using mercury intrusion porosimetry and scanning electron microscopy. The combination of mechanical and microscopy tests allowed further insight into the relationship between porosity and CSSM. The pore size distributions at the points selected are monomodal, and unique for a given state, independent of the stress path history. Lines representing the loci of normally consolidated states and critical states were drawn in terms of mean pore size against mean effective stress, but, unlike in CSSM, for the stress range investigated, the lines seem not to be parallel to each other. Examination of pore orientation using a fabric index shows that for this clay, very high isotropic stresses need to be applied to attain an isotropic fabric, while a constant fabric index seems to define the critical state line. Overall, states on the K₀ normal compression line and critical state line correspond to unique particle size distributions and fabrics that are independent of the paths taken to reach them and solely dependent on the stress levels, a framework that is consistent with CSSM.