Yielding of cement-mixed gravelly soil affected by viscous property, ageing and damage

The yielding of compacted moist cement-mixed gravelly (CMG) soil, subjected to arbitrary loading histories with two stress variables, is studied by means of non-standard drained triaxial compression tests. A non-linear three-component model is modified to describe the elasto-viscoplastic property affected by ageing and shear yielding-associated damage. The development of the inviscid yield locus (YL) is formulated based on the interactive double-yielding mechanism that comprises (i) the bounding mechanism controlled by “inviscid YL, YB” and (ii) the frictional mechanism controlled by “inviscid YL, YF”. Each inviscid YL is determined as an inner envelope of a given set of YB and YF that have developed by ageing and shear yielding and have been affected by damage. As the inviscid YL approaches the peak strength line, the shape changes in association with a decrease in the effect of YB and an increase in the effect of YF. The size and shape of the respective YLs in total stresses (i.e., measured effective stresses) are different from those of the corresponding inviscid YLs due to the viscous effects. The total stress-strain relation for a given loading history is obtained by accounting for the viscous effects from the inviscid stress-strain relation, which is obtained from the basic inviscid stress-strain relation accounting for the effects of ageing and damage. It is shown that this model can properly simulate the development of YL for a wide variety of loading histories applied along various stress paths.