Study on the characteristics of geogrids/soil interface

Large direct shear friction tests are conducted on reinforcement/soil interface in the paper, producing the shear stress-displacement curves and c & ϕ, the reinforcement/soil interface strength parameters under different testing conditions with various fill compaction degrees (90% and 93% respectively), different water contents (7.23%, 10% and 12%) and various geogrid bore diameters (5cm, 10cm, 15cm, 20cm). Based on the test results, an analysis is made on the effect of friction factor ratio on reinforcement/soil interface strength. The test and analysis results indicate that: (a) The friction angle of reinforcement/soil interface is, more often than not, slightly smaller than the internal friction angle of soil mass. Unless the water content of reinforcement/soil interface is far beyond the optimum water content, the friction factor ratio basically varies from 0.82 to 0.95; (b) The larger the compaction degree of fill, the larger the friction angle of reinforcement/soil interface; the higher the water content of fill, the smaller the friction angle of reinforcement/soil interface; when the ratio between d50 and geogrid bore diameter is around 0.05 (which is referred to as the optimum matching), the friction angle of reinforcement/soil interface is the maximum; (c) The water content of fill has a significant effect on the friction angle of reinforcement/soil interface. When the fill is close to saturation, the internal friction angle of reinforced soil decreases by 18.5% while the friction factor ratio is 0.51.