Bearing capacity and displacement characteristics of long-short composite piles in loess areas

The researches on new pile foundation are insufficient in loess areas. In order to introduce and promote the composite pile foundation with long and short piles in the loess areas, the bearing characteristics of pile foundation need to be further studied. The laboratory model test apparatus is developed. The model test apparatus is loaded through servo loading system under the single-pile, four-pile and eight-pile working conditions, and the bearing capacity of pile and deformation characteristic are comprehensively analyzed and studied. The results show that the axial force of pile and the side friction play with asynchrony, and the failure mode of the long pile is the pricking destruction, but the short pile is not obvious. Under the composite test of four-pile working condition, the limit value of bearing capacity of the pile is equal to that of the single pile, and the occurrence of the position of the maximum of skin friction is different from that of the single pile. The load-sharing ratio of the long pile is more than that of the short pile. Under the composite test of eight-pile working condition, the load among the corner pile is more than that of the edge pile and center pile under each stage loading, and the bearing capacity and the skin friction of the long piles (corner pile, edge pile) and short piles (center pile) obviously decrease compared with those of the single pile. The load sharing ratio of the corner pile is a little more than that of the edge pile.