Influence of testing conditions on the mechanical characterization of a soft volcanic rock

The results of laboratory tests, and the consequent values of the mechanical parameters, could be appreciably influenced by the characteristics of the testing device and by the adopted experimental procedure. Some of these effects, such as those related to the stiffness of the loading frame, are discussed here on the basis of a series of triaxial tests performed on samples of a soft volcanic rock (tuff) from central Italy. In particular, the influence is discussed of the "local" or "global" technique adopted for strain measurement on the overall shape of the stress-strain curve, and on the values of the elastic parameters determined before reaching the "peak" load level and in the "after peak" condition.