Determination of the confining effect of geogrid rein-forcement from large scale triaxial tests

Abstract

The immense contribution of geogrids to the strength of reinforced soil is well known in science and nowadays also increasingly accepted in the industry. Reinforced granular material is a composite material which combines properties resistance of two different materials in such a way to increase its bearing capacity. However, the differences between calculated and measured deformations of geogrid-reinforced structures indicate that the exact behaviour of geogrids in soil is not totally understood yet. To allow for better assessment of the composite behavior, a series of large-scale triaxial tests were conducted on unreinforced and reinforced gravel specimens of 50 cm in height and 23 cm times 23 cm in cross-section, using an apparatus developed at the Institute of Industrial Science, University of Tokyo (Anh Dan et al. 2006). In addition to the variation of the cell pressure, the test series also includes the variation of geogrid types. Results of unreinforced and reinforced test series showed a significant increase of the peak strength as well as a reduction of the deformations of the tested samples due to the reinforcement. A confining effect of the reinforcement was clearly identified and could be explained with a mechanical model. A calculation method, which is based on the mechanical model, was used to draw the stress paths for a series of reinforced tests.