Interface Properties of Geogrid and Fly Ash/Fly Ash-Tire Chip Mixtures

Disposal of waste materials like fly ash and tire chips is a major environmental concern. One of the possible applications of these waste materials is to utilize them as backfill materials in Mechanically Stabilized Earth (MSE) walls. The common modes of failure in MSE walls are (a) pull out mode of failure, and (b) sliding mode of failure. The sliding mode of failure can be studied by performing interface tests in the direct shear box to know the interface or sliding shear resistance offered by the reinforcement with respect to the soil under a given surcharge loading. In this study, it is proposed to use fly ash, and mixtures of fly ash and shredded tires as a backfill material. Hence, this study is carried out to quantify the interface shear resistance between the geogrid reinforcement and fly ash-tire chips mixtures. Ash from two different sources, Neyveli Thermal Power Plant and Ramagundam Thermal Power Plant, are used to study the interfacial shear strengths. The interface properties are also compared with the conventional fill material (like sand) and are found to be comparable. Four different percentages by weight of tire chips are mixed with fly ash (0%, 10%, 30% and 60%, by weight of dry fly ash) to prepare the mixtures. 30% and 60% mixes showed higher shear strength in the case of both the ashes. 30% mixtures are found to give higher interfacial shear strength in the case of Neyveli Coarse fly ash, and almost equal strengths for 30% and 60% additions in the case of Ramagundam Pond ash. The interaction efficiency of geogrid and both the ashes are calculated and is found to be in the range of 80-130% (with respect to cohesion and friction angles), and for the tire chips mixed ashes it is found to be in the range of 40-150% (with respect to cohesion and friction angles). The interaction coefficients between geogrid and fly ash is found to be in the range from 0.85-0.95, and for geogrid and fly ash-tire chips mixtures is found to be in the range of 0.75-0.98. This study suggests that the sliding resistance of geogrid reinforced ash is comparable with that of conventional fill material, and hence can be a competent material for backfill application