Accueil du site > Animation scientifique > Séminaires 2007 > 16/10 - Séminaire de Orencio VILAR - salle de réunion bat. G (ENSHMG) à 12h30

16/10 - Séminaire de Orencio VILAR - salle de réunion bat. G (ENSHMG) à 12h30

par Cédric LEGOUT - 10 octobre 2007

TITRE : Some topics about the shear strength and on the collapse of unsaturated soils.
The interest in unsaturated soil behavior has increased in last years. Many advances in oil modeling and in laboratory equipments have been proposed, however the major drawback when performing unsaturated soils tests still arises from the need of controlling or imposing soil suction. Soil suction is usually imposed through axis translating technique (Hilf, 1956), osmotic technique (Kassif & Bem Shalon, 1971), and relative humidity using saline solutions or is directly measured using mini tensiometers, psycrometers (Edil et al., 1981) or by high capacity tensiometers (Ridley & Burland, 1995). A common feature of all the experimental techniques devised to test unsaturated soils are that they are time consuming or complex or both, requiring an elevated degree of expertise. Thus, it is not surprising the large effort of researchers in proposing indirect methods to predict the basic soil properties, such as the unsaturated hydraulic conductivity (van Genutchen, 1980, among others) and shear strength (Oberg & Salfors, 1997 ; Vanapalli et al., 1996). This presentation will focus on some topics of mechanical tests on unsaturated soils with emphasis on measurement and interpretation of shear strength and on the study of soil collapse, the sudden volume decrease of a soil upon wetting under an almost constant overburden stress. A simplified testing procedure to estimate the shear strength of unsaturated soils is proposed, based on data from saturated samples (effective stress parameters) and from air dried samples without the need for suction control. Finally, some practical guides to identify the occurrence of collapsible soils are also presented.