The Degradation Behavior of Fabriano Soil During Cyclic Loadings

When the shear strain is higher than the so called volumetric threshold, degradation phenomena occur. In this paper the possibility of modelling the degradation behaviour of Fabriano soil with a simple law is examined. The study shows that a modified 2nd Masing Rule (Masing, 1926; Tatsuoka et al., 1993) is capable of well reproducing the experimental stress strain curve of natural clays during cyclic loading. The modified 2nd Masing rule assumes that the scale amplification factor for the unload-reload branches (n) is not necessarily equal to two as postulated by the original 2nd Masing rule. In particular, it was found that n = 6 in the case of stable cycles. When degradation phenomena occur, n decreases. The limited experimental data did not allow the authors to determine the dependence of n on shear strain (g) and number of loading cycles (N). On the other hand the degradation parameter (t) proposed by Idriss et al. (1978) was computed according to the procedure suggested by Lin and Chen (1991). The values of t resulted to be much higher than those available in literature. The results obtained for Fabriano soil have been compared with others data available in literature and in particular with the results obtained for undisturbed Augusta, Catania, Pisa clays and reconstituted Toyoura sand (Cavallaro, 1997; Lo Presti et al., 1998; Ionescu, 1999; Lo Presti et al., 2000).