Analysis of the mechanical response of an artificial collapsible soil

Natural collapsible residual soils are a common occurrence in Brazilian unsaturated deposits. The work presented in this paper is part of a larger project designed to identify the most important parameters controlling the mechanical behaviour of this type of material. A laboratory testing programme has been carried out in artificially unsaturated cemented samples reproducing some of the characteristics of natural collapsible soils. A technique for sample preparation has been developed, which has resulted in specimens with high values of void ratio and various degrees of cementation. In particular, it has been decided to use soil cemented mixtures with expanded polystyrene particles which has led to light samples with low density, meta-stable mechanic structure, and good workability. These artificial samples have been subjected to direct shear and oedometer tests, including conventional and suction-controlled oedometer tests. Oedometer tests have been used to characterize the behaviour of this material and to quantify the potential collapse due to loading and wetting. From the observed behaviour it is suggested that the initial void ratio, cement agent and initial suction are all important factors influencing the potential collapse of the soil. For saturated artificial soil samples the critical state lines in the (v, ln p')-plane and (q, p')-plane have also been calculated by using an approximated procedure based on the results of direct shear tests.