Master of Science in Civil Engineering (MSCE)


Civil and Environmental Engineering

Document Type



The cost of repairing pavements that fail before the end of their service life is enormous in the United States and it is continuously rising. Premature pavement failure is often associated with loss of support in the subgrade layer, especially in regions with fine-grained subgrade soils. Resilient modulus (Mr) is analogous to the stiffness of a subgrade and a key design parameter for pavements. Due to seasonal variation, Mr varies periodically due to changes in moisture content. However, Mr depends not only on moisture content but also the stress state of the subgrade, which for unsaturated soils is dependent on the matric suction. This study attempts to reinforce the relationship between Mr and matric suction by conducting Repeated Load Triaxial testing on four (4) different soil types and evaluating the Soil Water Characteristic Curves for each soil type. The SWCC curves are evaluated through the entire range of saturation by combining the axis-translation and chilled mirror hygrometer techniques. It is evident that Mr depends on matric suction, which also varies with moisture content, thereby, a Mr-matric suction relationship provides a sound theoretical framework to account for moisture variation in unsaturated subgrade soils. A modified constitutive Mr-matric suction relationship is proposed to accurately capture the stress state of the soil, and account for the variation in contribution of matric suction to Mr. For practical purposes, other methods to incorporate the effect of moisture variation on Mr values are evaluated. The variation in Mr was captured in terms of changes in degree of saturation. Statistical regression models, with the ability to incorporate moisture variation, are proposed to predict regression constants, k1, k2, and k3, for Mr constitutive models.



Document Availability at the Time of Submission

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Committee Chair

Abu-Farsakh, Murad