Experimental research on behaviors of geogrid-encased stone column-improved composite foundation under cyclic loads

To study the behaviors of geosynthetic-encased stone column-improved composite foundation under traffic loads, a series of laboratory tests on composite foundation reinforced by single geosynthetic-encased stone column subjected to cyclic loads are conducted. The composite foundation is instrumented to monitor the stress distribution between piles and soils, accumulated settlement, excess pore water pressure and column bulging deformation. The influences of the reinforcement configuration, tensile strength of geogrid encasement and thickness of sand bed on the cyclic behaviors of the composite foundation are investigated. The test results indicate that the pile-soil stress distribution is stiffness-dependent, and the vertical reinforced encasement improves the plie stiffness. The horizontal reinforced geogrid can further increase the loads to pile top, while the sand bed increases the loads to transfer to the surrounding soils. The accumulated settlement reduces with the increase of the tensile modulus of geosynthetic-encasement. Based on the settlement control, the geogrid with high tensile modulus should be selected as the geosynthetic encasement. The accumulation of pore water pressure in the composite foundation increases with the increase of the stress in the surrounding soils. The bulging deformation depends on the vertical loads on piles and the tensile modulus of the geosynthetic encasement.