Research on working mechanism of cushion in composite foundation with rammed soil-cement piles under flexible foundation

Based on shear displacement method, together with Mylonakis & Gazetas model for interaction between pile and soil, and the layered foundation model, the calculation formulae of the flexible factors for mutual action between pile and pile, pile and soil, soil and soil were obtained. Then, a new method, which considered the influences of cushion have been proposed to analyze the pile-soil-cushion interaction under the embankment, and the correlated program have also been developed by Matlab software. Meantime, combining with the model test results of the composite foundation with the rammed soil-cement piles under the embankment, the influences of the cushion modulus and thickness on the differential settlement between pile and soil were discussed. All of experimental and theoretical results showed that the appropriate soft cushion is beneficial to take full advantage of the pile, and the load sharing of surrounding soil and differentia settlement between pile and surrounding soil may be reduced, and the working properties of composite foundation were improved.