Geosynthetic-Reinforced Retaining Walls with Flexible Facing Subjected to Footing Loading

Geosynthetic-reinforced retaining (GRR) walls have been used as bridge abutments to support shallow foundations. This technology eliminates the need for traditional deep foundations, such as piles, to support bridges. However, limited studies have been conducted so far to evaluate the performance of GRR abutment walls constructed with flexible facing. The objectives of this study were: (1) to evaluate the performance of the GRR walls subjected to static footing loading and (2) to develop methods to predict facing lateral deflections and surface settlement of GRR walls under the footing loading. To fulfill the above research objectives, a comprehensive experimental study and analytical analysis were conducted. In this study, pullout tests were conducted to evaluate the effect of the load application method using an airbag with and without stiff plates on the vertical stress distribution and the pullout capacities and deflections of extensible (geogrid) reinforcement in the soil in a large pullout box. The non-uniform pressure distribution resulting from the airbag with stiff plates reduced the pullout resistance of the reinforcement as compared with that without stiff plates. The test results also show that the displacements in the cross section of the same transverse bar were not equal when the normal load was applied through stiff plates. This study investigated the combined effects of tension, bending, and friction on the measured strains on the upper and lower sides of uniaxial geogrid specimens by wrapping the specimen around a cylinder of different diameters. The test results show the combination of tension, bending, and friction reduced the average upper and lower strains by 28% as compared with the tension only. The cylinder diameter did not have any effect on the measured strains of the geogrid on the cylinder. The experimental study investigated eight reduced-scale GRR abutment walls with wrapped-around and modular concrete block facing subjected to static footing loading in a test box under a plane strain condition. The settlements of the footing, the lateral deflections of the facing, the vertical and lateral earth pressures, the tensile strains along reinforcement, and the failure mode were evaluated. The test results showed that the modular block facing acting as a relatively rigid structural element reduced the footing settlement as compared with the wrapped-around facing. Moreover, the maximum lateral deflection in the wrapped-around facing wall was much larger than that of the modular block facing wall under the same applied footing pressure. The measured maximum vertical stress was larger than the calculated stress from the Boussinesq equation and the 2:1 distribution method at the centerline of the footing. The maximum lateral earth pressure was recorded at the depth of 0.5H-0.7H and 0.9H (H is the wall height) from the top of the walls with modular block and wrapped facing, respectively. The Boussinesq equation was used to calculate the lateral earth pressure induced by footing loading, which approximately matched that measured for the wall with wrapped-around facing, but was quite different from that for the wall with modular block facing. Shallow, middle, and deep slip surfaces were observed in these test models at failure. This study also investigated the effect of footing loading on global stability of GRR walls with wrapped-around and modular block facing. The limit equilibrium methods (i.e., the Bishop modified method and the Spencer method) included in the ReSSA program was used to determine critical slip surfaces and their corresponding factors of safety of the eight reduced-scale experimental models and ten case histories in the literature. Based on the limit equilibrium analyses, the critical slip surfaces identified by Bishop's modified method and Spencer's two-part wedge method reasonably agreed with those observed in the walls under footing loading. The data analysis showed an exponential relationship between the calculated factor of safety using the Bishop method and the maximum lateral facing deflection or the surface settlement of the GRR walls under footing loading