Application of Stepped Isothermal Method for Estimation of Long-Term Cyclic Residual Strain of a Polypropylene Geogrid

During service, geosynthetic-reinforced soil (GRS) structures are often subjected to cyclic loading, such as traffic loading, which causes cyclic tensile loading to occur in the geosynthetic reinforcement. This cyclic loading results in the development of cyclic residual strain (Decyclic) in the geosynthetic reinforcement, which can cause excessive global deformation of the GRS structure. This research aims to examine the development of Decyclic in a polypropylene geogrid under various levels of tensile load (LL), as well as various double amplitudes (DA) and frequencies (f) of cyclic loading. To accelerate the process, an ambient temperature increase technique is employed, where the temperature is increased from 30°C to 50°C in steps while keeping it constant for one hour in each step. The test results were analysed to establish the relationship between Decyclic and the number of cycles (N_c) at the reference temperature of 30°C. These relationships were then used to examine the effects of LL, DA, and f. The study found that Decyclic increases with increasing LL, but decreases with increasing DA. The effect of f was found to be insignificant, suggesting that the rate-dependent property of the geogrid is the main factor contributing to Decyclic, while the rate-independent cyclic loading effect is insignificant.