Large-scale direct shear test on the interface between geogrid and gravel-soil mixture

When geosynthetics are used in various types of reinforced soil projects, the main problems are the stability, safety and long-term service performance of the reinforced structures. The friction characteristics of the reinforced soil interface have a direct impact on the stability and safety of the reinforced structures. However, there are many researches on clay and sand, and there are few reports on the interface interaction between gravel soil mixture and geogrid. In this study the reconstruction and extension project of Lanzhou-Haikou expressway from Nanning to Fangchenggang in Guangxi is taken as the background, the indoor large direct shear test of the gravel-soil mixture and geogrid interface shear characteristics are studied, and the effects of the different shear rate, degree of compaction and normal stress on the interaction characteristics of direct shear interface are discussed. The test results show that when the normal stress σ_v ≤30 kPa, the peak value of the interfacial shear stress presents a linear growth trend with the increasing compaction degree. With the further increase of normal stress, the growth trend changes from linear growth to polygonal growth. With the increasing shear rate, the shear stress at the interface between the reinforcement and soil is maximum at the shear rate v =1.5 mm/min. The interfacial cohesion increases with the increasing compaction degree, and the interfacial friction angle is just the opposite. Under different shear rates, the interfacial cohesion and friction angle fluctuate within a certain range of 38.725 kPa to 50.495kPa and 25.873° to 29.683°, respectively. The direct shear curve of the reinforced-soil direct shear interface is characterized by strain hardening, and the shear displacement corresponding to the inflection point under different influencing factors is mostly concentrated between 0.83% and 1.83% of the shear area length. The results can provide design parameters and theoretical reference for reinforced engineering construction with gravel - soil mixture as filler.