Experimental research on vertical bearing behavior of composite foundation constructed by caisson and piles

This paper introduced a new composite foundation that was made up of caisson and piles. The caisson was constructed first, and then piles were bored or jacked through the holes reserved in the concrete floor of the caisson. To study the vertical bearing behavior of composite foundation, four groups of model experiments for single caisson and composite foundation with different piles lengths were performed in sandy soil. The Q - s curves of single caisson and composite foundation in each level load were obtained. The distribution of soil pressure at the bottom of the caisson was given. The axial force and side friction of piles were analyzed. At last, the load bearing ratio of piles with different piles lengths were discussed. The results indicated that the existing of piles could bear the soil pressure, and could enhance the vertical bearing capacity of single caisson, so the vertical bearing capacity of composite foundation was better than that of single caisson. And the enhancement effect was increased with pile length increasing. In general, the caisson could bear the top load and could be used for construction platform in the construction of bridges. The piles under the caisson could control the settlement after the bridges were built.