DEVELOPMENT AND MECHANICAL PROPERTY ANALYSES OF EXPANDED COMPACTION PILES FOR ELIMINATING NEGATIVE FRICTION

To eliminate negative friction on piles in areas of poor soil such as collapsible loess, a new compaction pile with expanders which can eliminate negative friction and improve bearing capacity is proposed. Its structural composition and working mechanism are discussed in detail. According to the structural characteristics of the new pile, a diamond hole expansion model for the expanders is established. The expansion elastic-plastic solution of the expanders and the ultimate expansion angle are solved by the method of complex variable function. Then the calculation formula of the ultimate bearing capacity of the new pile is obtained. The compaction effect and bearing characteristics of the new pile are analyzed by the finite element method and the proposed theoretical method. The results show that: The influence range of the expanders on soil stress is approximately 2 to 3 times the expansion width of the expanders, and the plastic zones formed by expansion are equal in vertical and horizontal directions; There are some order effect and time effect for each expander in load-bearing process, and the bearing capacity of a expander is related to the properties of surrounding soil; The numerical simulation results are basically consistent with the theoretical results, which verifies the correctness of the theoretical analysis method in the paper; Compared with ordinary straight piles and tube piles, the negative friction on the new pile can be well eliminated, the bearing capacity can be obviously improved, and the force mechanism is reasonable. The study provides theoretical basis and reference for the design of pile foundation in collapsible loess areas.