Analysis of the Shear Strength of a Soil-Geosynthetic Interface

Abstract The paper presents the results of the shear strength measurements of a soil-geosynthetic interface. The tests were executed using a large-size direct shear test apparatus. A total of 5 different samples of materials were tested, i.e., ash, sand, well-graded gravel, fine poorly-graded gravel, and medium poorly-graded gravel. These materials were reinforced using different types of geosynthetics, i.e., Thrace WG80 black woven geotextile, Tencate Miragrid GX55/30 woven geogrid, and Thrace TG3030S rigid polypropylene geogrid. An interface coefficient α, which represents the ratio of the soil-geosynthetic interface shear strength to the shear strength of unreinforced material sample, was determined for given combination of the material and geosynthetics. The coefficient α reached a greater value in the critical stress state than in the peak stress state for sands and gravels reinforced using GX55/30 and TG3030S geogrids. The value of the coefficient α was in a range of 0.87 - 1.04 for gravels and 1.03 - 1.19 for sand. The black woven geotextile was used as the reinforcement only in samples of sand and ash. The results pointed to the different behaviour of these materials in the testing of the interface shear strength.