Experimental evaluation of mechanical behavior of unsaturated silty sand under constant water content condition

There are very few experimental data on the mechanical behavior of unsaturated soils, particularly in constant water content condition, because of the technical difficulties and time-consuming nature of measuring suction and deformation. This paper presents the results of a series of constant water constant triaxial tests on the specimens of an unsaturated silty sand. Constant water content tests correspond to a field condition where the rate of loading is much quicker than the rate at which the pore water is able to drain out of the unsaturated soil. The axis translation technique and a double-walled triaxial cell have been used to measure the soil matric suction and variation of pore air volume respectively. Test specimens were prepared at two different compaction conditions prior to testing to achieve different initial density. It is found that the mechanical behavior of the soil mainly depends on the initial density, the mean net stress and the initial matric suction. Also the volume and pore water pressure changes are significantly different in specimens with different initial condition. The results of tests indicated that the shearing strength of silty sand increases non-linearly with matric suction.

► Mechanical behaviour of the unsaturated silty sand was studied by triaxial tests.
► Shear strength increases with increasing normal stress, initial density and suction.
► Effect of suction on shear strength becomes less significant at high matric suction.
► The pore-water pressure changes are totally different in the unsaturated specimens.