Variability of soil stress-strain non-linearity for use in MSD analyses evaluated using databases of triaxial tests on fine-grained soils

The feasibility of a tunnel, foundation or excavation project is to some extent dependent on limiting the potential ground movements during construction. To make such an assessment it is important to quantify the stress-path dependent behaviour of the soil undergoing undrained lateral and vertical stress relief. At an early stage in the project, site-specific test data is limited and so predictions must necessarily be based upon expected characteristics of the soil deposit. Analysis of a recently compiled database RFG/TXCU-278 has demonstrated a method of quantifying the variability of stress-strain data from stress-path tests that are more frequently encountered in commercial practice (consolidated-undrained triaxial compression and extension tests) for use in design sensitivity analyses. A soil non-linearity parameter (b) is investigated using the database RFG/TXCU-278 and a series of previously reported tests performed on intact Bothkennar Clay. Evidence from both databases suggests that the variability of b is not strongly linked to the effects of shear mode, OCR, strain rate, or plasticity. It is shown that reasonable predictions of nonlinear behaviour up to a load factor (σmob/σfailure) of 0.8 can be achieved using the MSD-MSF method for a rigid pad test.