Geogrid stabilisation application – review of strain measurement methods, research and implications on design approaches

Abstract Geogrids have been used in the construction industry for stabilisation applications for decades, however, there is still a lot of conflicting information relating to the mechanical properties required to achieve this stabilisation function. Many designers adopt traditional tensile strength against tensile strain approaches that reflect membrane effect and ignore the actual mechanism of interlock and confinement. Recent ISO 10318-1:2015 defines geogrid stabilisation function by means of aggregate interlock and confinement, whereas tensile strength is seen as a function of reinforcement. Researchers across the globe have attempted to quantify the strain developed in geogrid used in a stabilising function exposed to heavy loads. Instruments used for monitoring typically comprise of standard wire strains gauges, fibre optics or foil strain gauges. Considering the harsh construction environment where the geogrids, and hence the strain gauges are exposed to damage or penetration by sharp aggregate edges, installation of sophisticated and sensitive monitoring systems can be challenging. There are several issues that can affect monitoring results such as the size of the monitoring instrument or the ability to achieve an adequate bond to the grid. Monitoring results have a major influence on geotechnical design and how practitioners perceive stabilisation mechanism in geogrids. Whilst the mechanisms of interlock and increased confinement have been studied, there still exists few design tools to provide designers with a straightforward analysis. This paper reviews research on the methods for in-situ strain measurement of geogrid installed in a stabilisation function, summarises results obtained by researchers and provides a summary of how these are reflected in geotechnical design approaches for geogrid stabilised soil.