Abstract: The tensile loss of warp knit type geogrids during installation is greater than that of membrane drawn type grids,while there are only few tests to determine the effect of site damage in China.A full-scale field installation test on warp knit type geogrid placed in four types of commonly used pavement subgrade material was performed to evaluate the amount and degree of installation damage.A series of tensile tests were performed to evaluate the reduction of strength due to the installation procedure.It was indicated that installation damage to the PVC coated PET grid was influenced by grain size distribution and angularity of backfill materials,and the reduction factor for tensile strength due to installation damage for PET geogrids varied from 1.3 to 2.6.Based on the test results,a reference range of the reduction factor by installation damage of the warp knit type geogrid was proposed.