Study of Non-Linear Stress Distribution and Permanent Deformation of Unbound Pavement Layers with Soft Subgrade under Various Stabilization Measures

The objective of this dissertation is to investigate non-linear stress distribution and permanent deformation (rutting) of unbound pavement layers with soft subgrade under various stabilization measures. Three studies have been undertaken to accomplish this objective. Firstly, a layered elastic approach is used to investigate the stress attenuation efficiency of the undercut stabilization measures now in use and the degradation of the efficiency during repetitive loading. Subgrade vertical stress responses collected from six laboratory and four in situ plate load test sections that incorporate different stabilization measures over soft subgrade are analyzed and discussed. The elastic modulus ratios of the stabilization and subgrade layers are back-figured and design modulus ratios of the various stabilization and subgrade layers are proposed to provide better information for selecting a design modulus for the stabilization layers.;Secondly, the responses of unpaved test sections that consist of aggregate base course (ABC) stabilization measures over soft subgrade under static loading are investigated using material models for modulus linearity, nonlinearity and anisotropy. Stress and deformation data from four large-scale plate load tests with different ABC thicknesses are analyzed, and the measured versus computed responses are compared for these material models. Vertical and horizontal stress distributions are assessed, and the impact of the modeling approaches on the estimated values is discussed. Analysis results indicate that nonlinear isotropic/anisotropic aggregate base modeling with a low level of anisotropy provides more realistic predictions for subgrade stress and horizontal tensile stress within the base layer than linear isotropic/anisotropic base modeling.;Finally, the rutting potential of soft subgrade foundations overlaid with different stabilization layers is examined. The results of repeated load triaxial tests conducted on soft subgrade samples are presented and discussed. The subgrade rutting responses of eighteen large-scale plate load test sections that incorporate various stabilization layers over soft subgrade are analyzed with computed values using calibrated rutting models. The impact of various methods (Boussinesq solution, elastic isotropic layered model and nonlinear anisotropic base model) determining subgrade stress states for the estimation of soft subgrade rutting is evaluated and discussed.