Large-scale direct shear tests on properties of geogrid-soil interfaces

The properties of geogrid-soil interface directly influences the safety and stability of reinforced earth projects. However, there are few researches on the interface properties of geogrid with different soil materials at the two sides of geogrid. A series of large-scale direct shear tests are conducted by using two-way geogrid as reinforced materials, silty clay with different water contents and quartz sand with different grain sizes. The effects on shear strength of geogrid-soil interface are analyzed under different influence factors, such as normal stress, water content of silty clay, shear velocity, grain size of quartz sand, and compaction degree of silty clay. The results show that the relationship between shear strength of geogrid-soil interface and normal stress is a linear correlation and in accordance with Mohr-Coloumb theory. The shear strength of geogrid-soil interface is influenced by the water content of silty clay. The shear strength index of interface is the highest at the optimum water content of silty clay. The shear strength of geogrid-soil interface is influenced little by the shear velocity and grain size, and their influence range is within ±10% and ±7%, respectively. The compaction degree of silty clay can improve the shear strength of geogrid-soil interface. The higher the degree of compaction is, the greater the shear strength-improving amplitude is. These factors must be considered properly in the engineering applications.