Based on the large scale direct shear apparatus (Shear box dimension: 500mm × 500mm × 410mm), a series of tests have been completed to investigate the shear strength characteristics of different backfill, compaction, moisture content, geogrid types, and shearing rate. A modified model of geogrid-soil interface shear strength was presented. The results indicate several conclusions: (1) Shear strength between geogrid and soil is smaller than that of soil; (2) For the same backfill material, the triaxial geogrid would be a better choice due to its better inter- action performance; (3) With regard to all the geogrid-soil interfaces, higher impaction degree or shearing rate results in larger shear strength; (4) For the same geogrid, sand gravel results in greater interface shear strength than cohesive soil does. For cohesive soil, the strength of geogrid-soil interface is more water content sensitive than soil itself; (5) the contribution of transverse ribs of uniaxial geogrid to the shear strength of geogrid-sandy other geogrids, and the interface shear strength of soil-longitudinal erface follows the friction law well, but it is the smallest among all parts of interface sheer strengths.
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