Design of Bridging Layers in Geosynthetic-Reinforced, Column-Supported Embankments

The cost of column-supported embankments depends, in part, on the spacing between the columns and the size of the columns and pile caps. Geosynthetic reinforcement is often employed in bridging layers to enhance load transfer to the columns and to increase the column spacing. The number, stiffness, and strength of geosynthetic layers are selected based on considerations of load transfer and deformation. In this research, a new method was developed for calculating the load on the geosynthetic reinforcement. The new method employs one of the existing mechanistically based approaches and combines it with consideration of the stiffnesses of the embankment, geosynthetic reinforcement, columns, and existing site soil. The new method was verified against the results of a large numerical parameter study, for which the numerical procedures themselves were verified against closed-form solutions for membranes, pilot-scale experiments, and field case histories. The new method for calculating load on the geosynthetic was integrated into a 10-step design procedure for geosynthetic-reinforced bridging layers in column-supported embankments. The design procedure addresses such details as the thickness and type of the bridging layer soil, selection of the geosynthetic reinforcement, if needed, and the embankment settlement. The necessary calculations have been programmed into a Microsoft Excel workbook. The workbook may be accessed at www.virginiadot.org/vtrc/main/online_reports/pdf/geogridbridge.pdf