Hydromechanical behavior and prediction of unsaturated loess over a wide suction range

Subgrade loess in arid and semi-arid regions subjected to high-suction conditions owing to low relative humidity and deep groundwater levels. Understanding the hydromechanical behavior of unsaturated compacted loess over a wide suction range is critical for resolving infrastructure problems in such areas. In this study, the water retention behavior of loess was investigated by imposing or measuring suction (s) using the axis translation technique, vapor equilibrium technique, and chilled mirror dew point technique. Triaxial tests were also performed to study the mechanical behavior of compacted loess under different net cell pressures (&#963;3n).The soil-water retention curves obtained using the different techniques are consistent. The degree of saturation and water content decreases significantly when s < 240 kPa, whereas the change of void ratio is relatively small. The water content versus s curves with different initial dry densities is coincident when s > 0.5 MPa, indicating that undrained triaxial tests can be considered as those under constant suction. For the same &#963;3n, specimens show strain-hardening, shrinkage, and drum-shaped shear failure under low-s conditions and strain-softening, dilatancy, and oblique section splitting under high-s conditions. The failure deviator stress and cohesion of the compacted loess specimens increase with increasing s over the full s range (0&#8211;299.37 MPa). An equation to predict the shear strength of unsaturated loess over a wide s range is proposed. The intersection of the capillary water retention curve and adsorption water retention curve is set as a reference point (sR), where capillary degree of saturation is applicable for s &#8804; sR and adsorption degree of saturation is added for s > sR. The predicted and measured shear strengths of the compacted loess specimens are in good agreement.