Shear strength behavior of compacted unsaturated residual soil

The focus of this paper is to study the shear strength behavior of a compacted residual soil from a site of the University of Sao Paulo in Sao Paulo, Brazil by conducting several series of experiments both under saturated and unsaturated conditions. The shear strength is a key property required in the design of foundations, construction of several geotechnical structures such as pavements, backfill material and embankments. A total of 57 unconfined compression tests and 57 constant water (CW) content triaxial tests were conducted on specimens compacted at three different initial water content conditions to study the shear strength behavior. One of the key objectives of the present study is to examine the influence of soil structure associated with different water contents and also the initial stress state on the shear strength. The matric suction in the soil specimens was precisely measured during the tests by using high capacity tensiometer (HCT). The experimental results suggest that the shear strength behavior is significantly influenced by the different initial compaction water contents. An empirical model is proposed using the results of the present study to estimate the three-dimensional (3D) failure envelope of the tested compacted residual soil for any condition of the initial stress state. Such a model is useful for the practicing engineers to estimate the shear strength behavior of the Sao Paulo residual soil for different loading and initial compaction water content conditions.