Evaluation of Composite Subgrade Reaction Modulus of Geosynthetic-Stabilized Recycled Subbase over Subgrade

When subbase exists, AASHTO design of concrete pavement is based upon the composite subgrade reaction modulus. This composite modulus depends upon the resilient modulus and thickness of the subbase, modulus of subgrade reaction, and base/subgrade loss of support during pavement life. Design charts are available in AASHTO to determine the design composite reaction modulus. However, these design charts were developed based on non-stabilized subbase over subgrade. Sustainability of geotechnical practice necessitates the incorporation of recycled materials for use in pavement construction. While the inherent properties of recycled materials may not match those of their virgin counterparts, landfill space, availability of natural resources, and cost will drive industry to use recycled materials despite their properties do not match those of virgin products. Geosynthetics have been increasingly used to stabilize subbase and subgrade for roadway applications. It is expected that geosynthetic stabilization will increase the composite subgrade reaction modulus and thus allow the use of recycled subbase materials in lieu of their virgin counterparts. However, minimal research has been performed to evaluate this benefit. In this study, plate loading tests were conducted to determine the composite subgrade reaction modulus in a large geotechnical testing box at the University of Kansas. For comparison purposes, non-stabilized and geosynthetic-stabilized subbases over subgrade were constructed and tested. Modification for loss of support is proposed to capture the performance of geosynthetic-stabilized base course. This paper evaluates the benefit of the geosynthetic, the effect on the subgrade modulus, and the viability of recycled materials for rigid pavement applications.