A New Method to Simulate Stress-Strain Relations from Multiple-Step Loading Triaxial Compression Test Results

Multiple-step loading (ML) on a single specimen can be used to determine the peak compressive strengths at different confining pressures (sigma'(h)s) of cement-mixed gravel (CMG) very similar to those obtained by single-step loading (SL) drained triaxial compression (TC) tests. However, only the unload/reload stress strain relations at different sigma'(h)s (except for the primary loading one at the first step) can be obtained from a ML test and the reloading relations become softer with an increase in the negative irreversible axial strain increment that has taken place during respective immediately preceding unloading regimes. This effect gradually decreased during reloading while it totally disappeared once large-scale yielding started. An empirical equation was developed to derive undamaged reloading stress strain curves (URCs) by removing the damage effects from ML TC test measured reloading curves (MRCs). A new simple method was developed in the framework of proportional rule to simulate primary loading curves (PLCs) at different sigma'(h)s from the MRCs from a given ML TC test using a correlation factor. A practical procedure for simulation of PLCs in a ML test were established and applied to generate PLCs in a ML test increasing sigma'(h) and a ML test decreasing sigma'(h). The method was validated by comparing the PLCs simulated from the results of a pair of ML tests increasing and decreasing sigma'(h) with those measured in a set of SL TC tests at different sigma'(h)s.