Field test study of pile-net composite foundation on oversized deep soft soil

Based on the treatment of soft foundation in Chaoshan railway station, monitoring sections and instruments are selected and embedded respectively for observing surface settlement, deep layered settlement, deep horizontal displacement, stress among pile spacing, and extension length of geogrid, etc. The results show that at the beginning of loading, stresses of both soil among piles and pile top will increase rapidly for a while; but the varying speed of stress on pile top is larger than that among pile spacing. When the filling hits a certain height, stress among pile spacing reaches extreme value; the occurring arch effect will make the central stress of four piles become less than that of two piles; the axial force and the side friction of pipe pile have close relationship with the stratum situation and raise along with the passing of time and growth of loadings; the layered settlement of foundation has positive correlation with the speed of embankment fillings; and the settlement value is related to depth and property of stratum. The tension displacement of geogrid ascends with the increment of filling height; and its increasing velocity undergoes a process of first slow then drastic and calm at last. The lateral displacement of embankment grows up with the increment of loadings and decreases along depth, and is effectively controlled by pipe piles.