Resilient Modulus of MnROAD Subgrade Soil

Laboratory remolded subgrade soil samples have been widely used to study subgrade resilient modulus. But physical conditions, such as moisture content and density, of such specimens may not represent in-situ conditions very well. Therefore, AASHTO and the Long-Term Pavement Performance program (LTPP) have recommended that undisturbed thin-walled tube samples should be used to study subgrade resilient behavior. The Minnesota Department of Transportation (Mn/DOT) is developing mechanistic-empirical pavement design approaches through the Minnesota Road Research project and has realized the importance of resilient modulus in the design approaches. Currently, the Mn/DOT is making an effort to study resilient modulus of unbound pavement materials through laboratory experiments. Under a research project at the Mn/DOT, several thin-walled tube samples of subgrade soil were obtained from six different pavement sections at the Minnesota Road Research project. Repeated loading triaxial tests were conducted on the soil specimens to determine resilient modulus at the Mn/DOT laboratory. Also, some soil properties, such as resistance R-value and plasticity index were obtained. R-value is an indicative value of performance when soil is placed in the subgrade of a road subjected to traffic. Two constitutive models (Uzan-Witczak universal model and the deviator stress model) were applied to describe the resilient modulus. The objective of the research was to compare these two well-known constitutive models in describing subgrade soil resilient behavior and to study effects of material properties on the resilient modulus.

From the specimens tested, the experimental results showed that the universal model described the subgrade resilient modulus slightly better than the deviator stress model and the coefficients in these two constitutive models were found to have correlation to material properties. Also, no well-defined relationships between R-value and the coefficients in the constitutive models were observed from the results of the tested specimens.

Content Note: This is the author’s version of a work that was accepted for publication in the Transportation Research Record: Journal of the Transportation Research Board, Issue Number: 1786, Publisher: Transportation Research Board ISSN: 0361-1981. The final version can be found at https://doi.org/10.3141/1786-03.