Alternative Testing Techniques for Modulus of Pavement Bases and Subgrades

Abstract

The importance of stiffness measurements has gained increased recognition in geotechnical applications in pavements. Two alternative testing techniques: bender elements and soil stiffness gauge (SSG) have been recently adopted as they show some potential and promising means of monitoring the stiffness and/or modulus of pavement materials. Since each technique has its own range of stress and strain levels, the relationship between the elastic moduli and nonlinear behavior exhibited by soils at large strains is required so that the measured modulus can be adjusted or corrected to a modulus corresponding to the desired strain levels. This paper presents the implications of these testing techniques in stiffness and/or modulus assessment of pavement bases and subgrades. To adjust the modulus measured in these materials, the desired strain amplitudes must be known. The strains incurred in the pavement base and subgrade layers that are subjected to the typical traffic loadings are summarized from a number of studies including finite-element analyses, large-scale model experiments, and in-situ test sections. The typical range of strain amplitudes imposed by the bender elements and the SSG is compared with those incurred in the pavement base and subgrade layers to evaluate their suitability in the assessment of pavement layer stiffness and/or modulus. Finally, some comments on the practical implications of these techniques to monitor the pavement layer stiffness and/or modulus are provided.