Experimental study of a naturally-weathered stiff clay.

Studying the shear strength of a naturally weathered clay is important to understand rain-induced slope failures in weathered soils. However, experimental studies on naturally weathered soils are limited. The paper focuses on the laboratory experimental investigation carried out to analyse the shear strength of a naturally weathered stiff clay that can be found in unsaturated conditions in situ. This has an important practical relevance in the evaluation of the stability conditions of natural slopes at clay outcrops. Different experimental techniques of suction measurement were used to obtain the soil-water retention curve of the clay over a wide range of suctions. Scanning electronic microscope (SEM) observations and results of mercury intrusion porosimetry (MIP) tests are also presented to highlight the considerable fabric arrangement modifications at the microstructural level induced by wetting–drying processes. Moreover, isotropic consolidated drained triaxial compression tests on undisturbed and reconstituted saturated specimens and controlled-suction triaxial compression tests on unsaturated undisturbed specimens were carried out. The test results allowed examination of the saturated mechanical behaviour of clay and comparison of the mechanical behaviour of the saturated material with that in an unsaturated condition.