Wetting simple shear tests on pyroclastic soils involved in shallow landslides

Shallow landslides are frequently triggered by rainfall in several geo-environmental contexts, and typical examples are those occurring in pyroclastic soil deposits of Southern Italy, where unsaturated soils are characterized by a metastable structure and may experience static liquefaction phenomena upon shearing. This paper describes some simple shear and wetting tests on remoulded specimens of an unsaturated pyroclastic soil performed through a Simple Shear apparatus equipped for unsaturated soil testing. The initial stresses of the specimens are those typical of a steep slope, and the stress paths reproduce a typical triggering mechanism for rainfall-induced shallow landslides. In the first stage of the tests, the net vertical stress was constant and the shear stress was increased at a fixed time rate. In the second stage, both the net vertical stress and the shear stress were kept constant and the suction reduced through the injection of water into the specimen from the bottom. In the tests, the soil exhibited mostly the same stress-strain behaviour during the shear stage, but different strain behaviour during the wetting stage.