Mechanistic-empirical approach to characterizing permanent deformation of reinforced soft soil subgrade

Abstract

This study focuses on characterizing the permanent deformation of geogrid-reinforced soft soil subgrade by using the mechanistic-empirical (ME) approach based on both experimental measurements and results of numerical modeling. Two sets of small-scale pavement sections were built over two types of soft soil subgrade and subjected to cyclic moving loads by means of a reduced-scale accelerated pavement testing (APT) device. Each set of pavement sections included one control section and three sections reinforced by different geogrids placed at the base–subgrade interface. The pavement sections were instrumented to measure vertical deformation and vertical stresses at the top of the subgrade. Strains developed in the geogrids were also measured by strain gauges throughout the construction and accelerated testing. Simplified finite element (FE) models were created to simulate both the control and geogrid-reinforced pavement sections and to compute the pavement mechanistic responses. With the experimental measurements from the first set of tests and results of FE analysis, the permanent deformation model in NCHRP 1-37A for unbound layers was adapted and calibrated to model the permanent deformation of the geogrid-modified subgrade. The effects of geogrids on the subgrade permanent deformation were integrated into the ME performance model through both the mechanistic response modeling and the empirical calibration. Predictions from the permanent deformation model were then compared with the second set of measurements and found to underestimate the permanent deformation of the geogrid-modified subgrade. However, the model was able to distinguish the difference in performance among the sections, i.e. the predicted rank of the performance was consistent with the measurements.