DEVELOPING TEST PROTOCOLS TO DETERMINE GEOSYNTHETIC MATERIAL PROPERTIES THAT BETTER REPRESENT TRAFFIC LOADING CONDITIONS

Geosynthetics have been successfully used for filtration, separation, drainage, moisture barriers and reinforcement in flexible pavements. Using them to reinforce the base layer of flexible pavements may provide savings either by reducing the thickness of the base or extending the life of the road. To quantify their potential benefit, it is essential to evaluate their intrinsic material properties under conditions pertinent to pavements. Standard tension tests, such as ASTM D 4595 and D 6637, apply monotonic loads to the materials to determine elastic moduli in their two principal directions. However, the types of loading conditions prescribed by these tests do not reflect conditions experienced by geosynthetics used as reinforcement in flexible pavements. Therefore, the purpose of this research was to develop test protocols that better describe the intrinsic material properties of geosynthetics pertinent to reinforced pavement design applications. Accordingly, cyclic loads and, to some extent, various strain rates and samples sizes were used to study their effect on these parameters. Three geotextiles and four geogrids were tested to compare their unconfined load/strain properties under monotonic and cyclic loads. Monotonic test protocols were used to study the effects of strain rate and specimen size on material properties. Wide-width monotonic tests were compared to wide-width cyclic tests. All testing was conducted using a servo-hydraulic loading system equipped with Curtis GeoGrips. Results from cyclic tests conducted on the geotextiles generally showed that the stiffness remained constant for all 1000 load cycles at a particular load level but that the stiffness increased significantly from one step to the next. Geogrids exhibited an opposite effect, in that the stiffness increased with increasing number of load cycles within a given load step, but did not change from step to step. Monotonic test results showed that the initial stiffness decreased as axial strain increased for geogrids, but remained constant for geotextiles. In most cases, the geosynthetics tested in this research showed noticeable changes in stiffness when strained at rates varying between 0.03% and 20% per minute. As expected, in nearly all cases the material behaved more stiffly as the strain rate increased. Tests conducted using varying samples sizes revealed that both length and width have a significant effect on the stiffness for the Amoco 2006 and Tensar BX1100 materials, tested in the machine direction. Additional work is necessary to fully establish the influence of load type, strain rate, temperature and confinement on the measured elastic modulus for conditions pertinent in pavements.

Language

  • English

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: 144 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00988102
  • Record Type: Publication
  • Report/Paper Numbers: Final Report
  • Files: TRIS
  • Created Date: Mar 24 2005 12:00AM