Shear strength and dilatancy of partially saturated sand in direct shear tests

It is well known that density, pressure and suction enhance the shear strength of unsaturated sand. However, little is known on the influence of all three together. Two series of direct shear tests have been conducted on two different silica sands at different densities and at low net stresses in order to investigate the influence of partial saturation on sand at different densities. The results show that the enhancement of the peak strength is more significant than the enhancement of the critical state strength and that the dilatancy rate is also enhanced. The stress-dilatancy analysis shows that the peak strength enhancement is the consequence of the critical state strength and dilatancy rate enhancements. A third sand, available in the literature, confirmed the findings.