Etude du comportement mecanique d'un gravier a l'aide d'essais triaxiaux en conditions saturees et non saturees

Compacted granular soils are widely used in the construction of various civil engineering works. These soils are unfortunately rarely studied by researchers in the unsaturated state. The analysis of their behavior is based on the determination of their mechanical properties such as shear strength and Young's modulus.;The soil-water characteristic curve (SWCC) that describes the quantity of soil water in relation to suction is considered the most important function of mechanical unsaturated soils. It allows to better understand soil volume behavior and the estimation of the fundamental properties of unsaturated soils such as shear strength and hydraulic conductivity. Few studies on gravels have been performed to experimentally determine this curve in function of the influence of the net confining stress, specifically on the sorption -desorption paths and on the air entry value. This work has for objective to partly answer to the lack of studies in this field.;The main goals of this study are to determine the mechanical properties of granular soils in the saturated and unsaturated state. The study will focus on influence of state variables (matric suction and net confining stress) on soil properties under variable water content conditions. Among other considerations, the study will include an experimental evaluation of the influence of the net confining stress on properties of the soil-water characteristic curve such as volumetric behavior and air entry value.;To achieve these goals, a number of triaxial tests were performed under the following conditions: consolidated drained, constant water content and under conditions to determine the SWCC on a granular material. The granular material of this study is a gravel designated by the GW-GM symbol and was obtained from the Moncton Crushed Stone quarry. Tests were performed with a modified triaxial apparatus (GDS) where suction could be measured and controlled through the translation axis technique.;Experimental results on the granular soil in the saturated state permit to observe significant increases in the shear strength and Young's modulus with increasing net normal stress. Undrained tests show that increasing matric suction and net confining stress lead to increasing shear strength and Young's modulus. This strength improvement is more affected by the net confining stress than by has a more pronounced role on pore water pressure variations. Apparent cohesion increases dramatically with matric suction. Changes in suction and in net confining stress produce a nonlinear effect on the angle &phgr; b. As for Young's modulus, it increases in a nonlinear manner with increasing matric suction and net confining stress.;The SWCC test results indicate a net confining stress influence on the shape of the curve paths, particularly the water sorption one. The action of increasing state variable values leads to an increase of the air entry value, the residual suction value and of the residual water content. The air entry value found is small. The study of mechanical properties in relation to the soil-water characteristic curve of granular soils in an unsaturated state proves to be essential to better understand soil behavior and to find appropriate technical solutions to many problems encountered in geotechnical engineering.;Keywords: Unsaturated Granular soils, soil-water characteristic curve , triaxial test , air-entry value, net confining stress , suction, shear strength, Young's modulus , sorption--desorption.