Investigation on geogrid reinforcement and pile efficacy in geosynthetic-reinforced pile-supported track-bed

This paper presents a full-scale model study of geosynthetic-reinforced pile-supported (GRPS) track-bed to investigate the effect of geogrid reinforcement and the evolution of pile efficacy (ratio of load borne by the pile cap to the total applied load). Three testing procedures were followed: model construction, static loading and subsoil settlement (simulated by discharging of water bags surrounding the pile caps). The results indicated that partially mobilized soil arching was developed during the first two procedures. When sufficient subsoil settlement was reached, fully mobilized soil arching was established. The geogrid was proven to effectively transfer load from the water bag to the pile cap. The stress difference induced by the geogrid showed lower absolute values for the corresponding sensors above the water bag during loading and settlement procedures, due to the inverse triangular distribution of the vertical-directional geogrid tensile force above the water-bag area. The experimental results of pile efficacy were compared to the estimations of four analytical models. For the present test at partially mobilized arching state, the pile efficacy increased with the construction height increasing and decreased as the static loading increased. The partially mobilized arching also resulted in overestimations of the pile efficacy from all four analytical models. At fully mobilized arching state, the pile efficacy stayed relatively stable, being well predicted by all four analytical models.