Geogrids must have a minimum tensile strength to make sure the product is not damaged during the placement and compaction of aggregate. However, no correlation has ever been shown between tensile strength and the performance of geogrids used for roadbed applications.
Geogrids are synthetic products that have large openings between rib structures and allow for rock to strike from one side of the product to the other side. This allows for rock to become confined within the opening.
Geotextiles are textiles made from synthetic fibers.
Biaxial geogrid was invented by Tensar in the late 1970s. Biaxial geogrids have square or rectangular openings, called apertures. Different types of biaxial geogrids exist on the market, but for roadbed applications, testing has consistently shown that integral geogrids made by a process known as punched and drawn perform best.
TriAx geogrid has additional diagonal ribs that increase the in-plane stiffness of the product. The triangular pattern is formed into a hexagon to improve how the product absorbs the forces from traffic loading. Ribs in TriAx are designed to provide a high aspect ratio which provides better interlock with the surrounding aggregate.
No. *This is shown by some of the testing outlined in the long answer of #1 above. Geogrid strength does not correlate to in-ground performance. The ability of the geogrid to interlock and confine the aggregate under wheel loading is important. This can only be measured through full-scale in-ground testing under wheel loads. Property characteristics such as rib shape, aperture shape, rib thickness, in-plane stiffness, junction style, and many other factors are contributors to the amount of interlock and confinement achieved.
No. Triax has a different geometry, different rib shape and different style types than BX. It works differently than BX geogrid and a design with TX is different than a design with BX.
Short answer: Yes. There are different design methods and inputs for each design. The allowable amount of permanent deformation also differs for both of these applications. They require different testing, and have significantly different failure criteria.
Performance is not based on index properties. It is determined empirically, using full scale in-ground testing. Request a copy of the design inputs, using the Giroud-Han method as outlined by FHWA, that were used as the basis of equivalency. Also ask for the full-scale testing, on the product being submitted (not another “similar product”), and the letter or report from the authors of the Giroud-Han method verifying that the testing and calibration were performed properly. Once you have this information, you will be able to compare performance related sections and evaluate equivalency.
Performance is not based on index properties. It is determined empirically, using precise, full scale in-ground testing. Require a copy of the 3rd party testing on which the supplier is basing its claim of equivalency. This testing should include Accelerated Pavement Testing (APT), performed on paved sections, following the procedures defined by NCHRP report 512. There should be multiple sections tested over different subgrade conditions and different pavement section thicknesses. Require a 3rd party review, by pavement design experts, verifying that the design values and methodology used are supported by testing for that product, and follow the guidance of AASHTO in R50-09 (“Geosynthetic Reinforcement of the Aggregate Base Course of Flexible Pavement Structures”). Also require 3rd party field validation testing, following AASHTO T221-90 (2012), to demonstrate that the results obtained in the field support the assumptions used in the design methodology, and that deformations are in-line with predictions.