Volume 27, Issue 5 (September 2004)
Strain Measurement of Geogrids Using a Video-Extensometer Technique
The paper describes a novel technique to record displacements and compute local strains at the surface of typical geogrid soil reinforcement products using a noncontact high resolution digital CCD camera (video-extensometer) technique. Specimens of biaxial polypropylene (PP) geogrid, knitted polyester (PET) geogrid, and uniaxial high-density polyethylene (HDPE) geogrid were subjected to in-isolation wide-width strip tensile loading under constant rate of strain (CRS), constant load (creep), and stress relaxation load paths. The specimens were gripped using a set of split roller clamps. Targets painted on the surface of the specimens were tracked in both vertical and horizontal directions using a commercially available CCD camera with ancillary hardware and software. The paper examines repeatability of the test methodology and demonstrates the ability of the method to record strains at high resolution up to rupture and to identify nonuniform distribution of axial and lateral strains in geogrid specimens.