Variation of Resilient Modulus of Subgrade Soils over a Wide Range of Suction States

AbstractDesign of flexible pavements over fine-grained soils requires determination of subgrade resilient modulus over a wide range of degree of saturation and suction for different soils. A novel experimental setup was developed by integrating a cyclic triaxial apparatus with capability to control suction using axis-translation and automated vapor pressure control to the specimen gas phase. System performance was evaluated through repeated load triaxial (RLT) tests for suction ranging from 0 kPa at saturation to 600 MPa at drier conditions. Replicate tests performed on a silty soil and a high-plasticity clayey soil indicated excellent repeatability. Resilient modulus of the materials is essentially unaffected with drying at low-suction range near the air-entry value and the optimum moisture content condition. This property then increases rapidly with subsequent drying until reaching a residual state after which the rate of increase in resilient modulus with respect to suction decreases to a low value. Limitations of a recent prediction model in capturing this trend demonstrated the need to determine resilient moduli over a wider range of suction for developing robust resilient moduli prediction model.