In this study, shear strength performances of different aperture size and shaped geogrids located between subbase and subgrade were investigated. Five different types of geogrids (5 cm x 5 cm, 4 cm x 4 cm, 3 cm x 3 cm square aperture size, hexagonal and crosswise aperture size geogrid), were tested and their shear strength values were analysed. Geogrid radial and horizantal displacements in pullout test box were measured by utilizing digital image process and strain gage sensors. Shear strengths of geogrids in the pullout test box between subbase and subgrade were also modelled by MATLAB programme. Finally, the usage of tested geogrid samples were researched for their highway performance under varying subgrade elastisity modulus values. Radial stresses occuring in highway subgrade layers that have different elastic modulus were numerically analysed and ELSYM Finite Element Analyses Programme.
The pullout test results of 4 cm x 4 cm, 3 cm x 3 cm and crosswise aperture size geogrids were % 5 lower than the tensile test results of them; pullout test results of 5 cm x 5 cm and hexagonal shaped aperture size geogrids were % 15 higher than tensile test results of them. As a result, hexagonal shaped aperture size geogrid showed good results in terms of both rupture at peak point and retained its strength after rupture. 5 cm x 5 cm aperture size geogrid showed close strength values with hexagonal shaped aperture size geogrid and gave the best results among the square shaped aperture size geogrids.
Key Words: Geogrids, Pullout Test Box, The Layers of Highway Subbase-Subgrade, Shear Strength, Digital Imaging Process.