The interaction among embankment fill,horizontal geotextile,pile(cap) and subsoil was analyzed based on the principle of minimum potential energy,and pile efficacy was obtained.

Theoretical solution suggests that the inclusion of geosynthetics in the fill enhances the pile efficacy and reduces the differential settlement when the soil arch is in plastic state;when the soil arch is in elastic state,there is no much difference between the cases with or without the geosynthet.

An analytical solution for pile efficacy is obtained.

First,through theory analysis,the pile-soil stress ratio and pile-soil load share ratio are considered to be important parameters reflecting the working property of cement-soil pile composite foundation.

Through the comparison of the model test result s and the numerical ana lysis, the loading transfer mechanism of pile in four?pile foundation is summar i zed, the back pressure characteristic of the cap and the additional pressure dis tribution in the soil are depicted, and the load sharing behavior of piles and s oil is compared.

The load sharing among piles and soil as well as the settlement of foundation varied with change of superstructure loads were observed in construction and in the early service.