Field Comparative Experiments of Pipe Pile Composite Foundation with Different Cushion Layers

In order to compare the stress and evaluate the ability to control deep soft soil settlement of three kinds of composite foundations, field experiments were carried out. Each pipe pile composite had a different cushion layer; a reinforced concrete slab, a geocell, and a geogrid, respectively. For the geocell and geogrid composites, a pile cap was added.Both the stress response, and the settlement, of the pipe pile composite foundations, under different cushion layers, were analyzed. The results show that the stress of both the pile's top surface and the soil between the piles was gradually reduced, from the subgrade center to the shoulder. The pile-soil stress ratios were 2.47-5.42, 2.30-6.25, 8.05-14.81 for the geogrid-reinforced cushion layer, the geocell-reinforced cushion layer, and the reinforced concrete slab cushion layer, respectively. As the load of the subgrade filling increased, the tensile strength of both the geogrid and the geocell gradually increased, and maximum tension occurred at the shoulder. The tensile strength of the geocell was greater than that of the geogrid, under the same load. The composite foundation of a pipe pile, plus a reinforced concrete slab is the best for controlling the settlement of the subgrade filling, and the settlement of the ground surface contributes 68.46% and 72.56% of entire settlement of the pipe pile-pile cap-geogrid and the pipe pile-pile cap-geocell composite foundations, respectively.