Evaluation of pavement design input parameters of biaxial and triaxial geogrid stabilized flexible pavements overlying soft subgrades

Stabilization of flexible pavement layers using geogrids to improve the mechanical response of pavement layers is gaining importance over conventional stabilization techniques due to their low cost and superior performance. However, the lack of experimental data on quantifying the design input parameters of stabilized subgrades or granular layers limits the extensive use of geogrids in the field. Evaluation of design input parameters such as modulus improvement factor (MIF) or layer coefficient ratio (LCR) would promote the use of geogrids in the pavement, reducing the consumption of natural aggregates and the overall project cost. This study attempts to evaluate MIF and LCR due to geogrid stabilized soft subgrades considering different scenarios. All possible combinations of stabilization of pavement layers using biaxial and triaxial geogrids were considered. This involved stabilization of (a) the subgrade layer alone, (b) base layer alone, and (c) subgrade, subbase, and base layers. Accordingly, an extensive, systematic experimental program consisting of eighteen large-scale model pavement experiments (LSMPE) were conducted in five categories (designated as Series I through V). The stabilization of subgrade and granular layers was carried out using commercially available biaxial (BX1 and BX2) and triaxial (TX1) geogrids overlying soft and moderate subgrades with California bearing ratio (CBR) equal to 2.5 and 4%. Test results showed that stabilized subgrade prepared with existing and prepared subgrade material in conjunction with geogrid improved the effective CBR to as high as 10.9% from effective CBR = 7% corresponding to existing and prepared subgrade material without geogrid. The design inputs of geogrids (BX1/BX2/TX1) stabilized granular layers resulted in the MIF and LCR values ranging from 1.9 to 2.8 and 1.31 to 1.63, respectively, for the tested configuration considered in the study. Based on the findings of the study, inputs on resilient modulus of pavement layers were recommended for similar reinforcement and subgrade conditions considered.