Effect of Cement and Saturation on the Stress-Strain Behavior of a Silty Clay

Matric suction and cementation together have significant influence on the stress-strain behavior of many lightly cemented soils. The combined effects of suction and cementation during soil formation may stabilize the fabric of the soil at a very high void ratio. This is the case of wind-blown loess of the Pampas formation in Argentina. The scope of this work is to present some fundamental aspects related to the unsaturated stress-strain behavior of lightly cemented silty clay. Triaxial test were performed in laboratory and strains were monitored by means of local displacement transducers. Undisturbed structured specimens as well as remolded unstructured specimens were tested both in saturated and unsaturated condition. It was observed that cementation and unsaturation cause an increase in yielding stress and shear strength, decrease in volume contraction during loading, and a higher propensity to stress localization. These effects are mainly controlled by water content and confining pressure. At low confinements, the unsaturated and cemented specimens behave more brittle as compared to the uncemented specimens due to the much lower deformation threshold required to break cementing bonds than menisci. A bilinear model is proposed to model the fragile behavior of cemented specimens.