Shear Behaviour of Geosynthetics in the Inclined Plane Test – Influence of Soil Particle Size and Geosynthetic Structure

This paper reports the investigation of the shear behaviour of six geosynthetics with two granular soils. The test equipment, soils, and geosynthetics properties are described and the soil-geosynthetic interaction behaviour is studied. The influence of soil particle size, geosynthetic structure, and test method are discussed by analysing the results of inclined plane tests. The main conclusions of the study are as follows: geosynthetic structure has an important influence on the soil-geosynthetic interface friction angle; higher soil-geosynthetic interface friction angles are measured when the geosynthetic surface has significantly sized apertures (e.g., geogrids) or allows the penetration of soil particles into the geosynthetic (e.g., nonwoven, spun-bonded geotextiles); geosynthetic surface roughness (e.g., geomembranes) is associated with higher soil-geosynthetic interface friction angles; soil particle size has an important influence on the soil-geosynthetic interface friction angle; broadly graded soils with large average soil particle sizes allow an increase in the soil-geosynthetic interface resistance; the method of test does not significantly influence the soil-geomembrane or soil-geotextile interface friction angles (geosynthetics with continuous surfaces); and the validity of evaluating the soil-geogrid interface resistance using a rigid support (Test method 1) depends on the structure of the geogrid. It is suggested that site conditions is the greatest factor to consider when selecting the most appropriate test method.