Non-Linear Stress-Strain Modelling of Geomaterials under Stable and Unstable Cyclic Loading

The paper shows that a modified 2nd Masing Rule (Masing 1926) 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 & Chen (1991). The values of t resulted to be much higher than those available in literature.