Isotropic yielding of unsaturated cemented silty sand

Unsaturated cemented soils are frequent both as designed materials and as naturally occurring layers. Both desiccation and cementation act separately as hardening mechanisms, but it is not clear how exactly their effects combine. Do they enhance one another? Are they mutually reinforcing? This study presents results from an experimental campaign aimed at answering these questions. Five different mixtures of soil (a granite saprolite) and cement (with cement contents in the range 0% to 7% on a dry weight basis) are tested in isotropic compression at four different water content levels. Initial void ratio is also controlled, using two initial compaction densities. Loading is performed at constant water content and suction is inferred from a set of water retention curves obtained from parallel psychrometric and pore-size distribution measurements. The range of yield stresses explored in this study covers almost two orders of magnitude and extends up to 7 MPa at suction values of up to 14 MPa. Both desiccation and cementation increase yield stress, but their effects are less marked when both act together, and therefore they are not mutually reinforcing.