Study On The Creep Property Of Geogrid And Its Effect On The Geogrid-soil Interface Property

In this paper, the creep tests of 1000 h were conducted on two kinds of Polypropylene bidirectional geogrid under the different stress level. The shrinkage measures were done after the cr eep tests and unloading completely. The test results showed that, under the load level of 40%, the values of final strain of the two kinds of Bidirectional geogrid specimens were less than 10%, and the creep rate of the Bidirectional geogrid is slower than that of the Uniaxial geogrid. Besides,the developments of the creep for the various parts of the geogrid specimens were nonuniform in the process of the creep. The observation of the shrinkage of the geogrid samples were measured as soon as unloaded. On the other hand, by using the Kelvin and other models to simulate the process of the shrinkage tests, an equation is setted up to describe the shrinkage of the geogrid. The experimental datas are fitted well with the equation.In order to study the influence of the creep property of the Bidirectional geogrid on the reinforced sand, the characteristics of the interface between the geogrid and the sand were studied by using the large direct shear test. Through experimental study, the results indicated that the internal friction angle of reinforced sand and the pure sand was basically the same; The sand will obtain an additional “cohesion” when the sand were reinforced by the geogrids. In the shear process, the rules of shear stress of the reinforced sand specimens changed with shear displacement were basically the same. The shear strength increased with the increasement of vertical stress and the shear displacements were gradually increased too, when the specimens were failure.Through the comparison of the shear test results of the reinforced sand samples with creeped geogrid, the reinforced sand samples with uncreeped geogrid and the pure sand samples, the creep property of geogrids had influence on the shear strength of reinforced sand. The “cohesion” of the reinforced sand samples with uncreeped geogrid was higher than that of the reinforced samples with creeped geogrid. Under the same vertical pressure, the value of the “cohesion” declined was up to 28% and the decreasement incerased with the load level of creep icreased. It is concluded that the creep of the geogrid may cause the decreasement of whole reinforced soil structure’s bearing capacity, which may lead to the generation of the large deformation, and further affect the safety of the project.