Relative Operational Performance of Geosynthetics Used as Subgrade Stabilization
Started: December, 2011 Ended: July, 2014 Project ID #4W3850 Status: Completed
Results & Findings
As described in the final report, full-scale test sections were constructed, trafficked and monitored to compare the relative operational performance of geosynthetics used as subgrade stabilization as well as determine which material properties are most related to performance. Seventeen, 50-ft. long test sections were constructed – fourteen containing geosynthetic reinforcement and three without. A subgrade material was prepared and constructed to an average strength of 1.79 CBR with the exception of two reinforced test sections which were constructed to greater and lesser strengths in order to determine the effect subgrade strength had on the performance of the test sections. The test sections were constructed with an average base course thickness of 10.9 in. with the exception of two controls where the base thickness was intentionally increased to evaluate the effect of base thickness on test section performance. Information from the test sections that were purposely constructed with different subgrade strength and base course thickness were used to correct any variability in the remaining reinforced test sections. Test sections were trafficked using a 45-kip, 3-axle dump truck. Rut, displacement, strain, and pore-water pressure were monitored during trafficking. Post-trafficking excavations were conducted to evaluate damage to the geosynthetic, base contamination from the subgrade, and strength and deformation of the layers. Longitudinal rut was the primary indicator of performance. Geosynthetic material properties were used in a linear regression analysis to determine which properties best related to performance of the test sections in this study as well as test sections from Phase I. It was determined that the strength and stiffness of the junctions and tensile strength properties in the cross-machine direction correlated well with performance. The woven and nonwoven geotextiles also performed well, but further research is needed to determine which material properties correspond to performance. Additional work is needed to more confidently specify minimum values for geosynthetic material properties associated with good performance in subgrade stabilization applications.
The main objective of this project is to determine material properties of geosynthetics that affect in-field performance of geosynthetics used for subgrade stabilization, so that DOT personnel can objectively and confidently specify appropriate geosynthetics based on material properties and cost for a specific situation, while also allowing competition from different manufacturers.
State departments of transportation (DOTs) routinely use geosynthetics for subgrade stabilization. This construction practice involves placing an appropriately specified geosynthetic on a weak subgrade prior to placement of roadway subbase. The geosynthetic provides stabilization of the subgrade by increasing the load-carrying capacity of the system and maintaining separation between the soft subgrade and subbase materials. Subgrade stabilization allows for a firm construction platform to be built with less aggregate and less construction time as compared to construction without the stabilization geosynthetic. There is a general consensus concerning the effectiveness of geosynthetics in this application; however, there is a lack of understanding and agreement on the material’s properties needed for performance. Those properties should be specified in order to ensure its beneficial use and to allow a broad range of products to be considered. Many state DOTs currently allow both geogrids and geotextiles to be specified. As an example, at the Montana Department of Transportation (MDT), the current specification for a geogrid does not follow a standard specification; rather, it is written on a project-specific basis. It is typically written for a biaxial geogrid and specifies minimum values for the principal properties of ultimate tensile strength, strength at 2 percent strain, aperture opening size and junction strength. For a geotextile, a standard specification is used and is based on survivability properties and permittivity values. In order to provide for the most economical geosynthetic selection while minimizing conflicts and promoting competitiveness, MDT and other states are interested in conducting a study to examine the performance of various geosynthetics for subgrade stabilization with the aim of relating this performance to material properties that can be incorporated into their standard specification to allow for a broad and economical use of geosynthetic products for a specific application.
Files & Documents
- Report by
- Document by
Sponsors & Partners
- Montana Department of Transportation (MDT) Sponsor