Abstract: Pile-net composite foundations can be used to minimize the vertical and horizontal displacements of embankments on soft clay foundations. The behaviors of clay foundations stabilized by dry jet mixing piles combined with geogrid are studied，including settlement, excess pore water pressures and soil pressures. According to testing results, changes of pressures on and below geogrids , stress ratio of pile to soil, dissipation of excess pore water pressure and the relation of settlement and soil pressure are analyzed. .From that, it can be concluded that (1) the excess pore water dissipates slowly, but its value is not larger than the above loading; (2)geogrid can improve the average result of soil pressures and can make the stress ratio of pile to soil large, and at the same time ,based on distribution of soil pressure of each cross section ,the viewpoint of arching effect is put forward; and (3) settlement is generated mainly by compress of the underlying clay and piercing deformation and self-deformation of dry jet mixing pile; the testing data provide useful information for theoretical analysis and designing.

Key words: dry jet mixing pile, geogrids, dry jet mixing pile-geogrid composite foundation, soil pressure, stress ratio of pile to soil, arching effect, excess pore water pressure