Quantifying Geogrid Benefits in Highway Pavements with In-situ Tests & Bender Element Field Sensors

Abstract: Geogrids have become essential in enhancing pavement performance, particularly through geogrid-aggregate interlock, leading to the formation of a mechanically stabilized layer (MSL). Past research has established the existence of MSL; however, current practices lack comprehensive data quantifying the benefits of geogrids for informed pavement design. Furthermore, understanding the impact of load-related stress states on the stiffness distribution within the MSL can optimize geogrid use in pavement bases. This paper will present the use of in-situ testing and embedded sensor technologies to quantify benefits of geogrid-stabilized unbound aggregate layers in highway pavements. In particular, the use of Bender Element (BE) field sensor technology allows for the measurement of local stiffness enhancement near geogrid. The study was conducted on three 250-feet long sections instrumented during US-20 highway reconstruction project in Elkhart, Indiana. One section served as control with no geogrid while the other two were configured with geogrids at the base-subgrade interface and mid-layer, respectively. Each section was instrumented with BE field sensor, pressure cells, temperature and moisture profilers, and concrete strain gauges. Dynamic Cone Penetrometer (DCP) soundings were performed at each BE field sensor and pressure cell location. Furthermore, in-situ testing using Automated Plate Load Testing (APLT) was performed directly on top of pressure cells and BE field sensors to evaluate the critical pavement response and stiffness under varied stress states. This method allowed for tracking changes in the in-situ resilient modulus and small strain modulus, providing a comprehensive understanding of the pavement's mechanical behavior. The study’s findings demonstrate the efficacy of geogrid reinforcement in highway pavements. Sections equipped with geogrids consistently exhibited higher in-situ composite resilient modulus (MR-Comp) and a lower rate of permanent deformation (∆δ). Similarly, sections with geogrids placed in the base layer exhibited relatively higher shear wave velocity (VS) indicating higher stiffness. These results provide quantitative evidence of the stiffening effect imparted by geogrids, effectively quantifying the MSL. The observed benefits over control section were consistent regardless of the geogrid's placement depth within the pavement structure. By quantifying the benefits of using geogrids in pavement foundation, this study offers valuable insights for pavement designers to develop optimized, sustainable, and cost-effective pavement solutions.