Research On Bearing Behaviors And Applications Of Prestressed Concrete Uplift Pipe Piles

Due to the characters of crack resistance, faste construction speed and cheapness, prestressed concrete pipe piles were widely used as uplift piles. The bearing behaviors and tensile strength of prestressed concrete uplift piles and connected components are very complex. there are many views against using prestressed concrete piles as uplift piles. In this paper, based on numerical simulation and test data analysis, the following contents were analized, and corresponding conclusions were gained.(1) Based on pile-soil interaction numerical simulation of uplift piles, the influence of pile length, pile diameter and soil conditions to bearing behaviors and distribution patterns of frictional resistance were were gained. Due to the smalle deformation of short pile, the working process of frictional resistance was at the same time, and the loading-displacement curve is broken line. Due to the large deformation of long pile, the working process of frictional resistance was not at the same time, and the loading-displacement curve is continuous curve.(2) Due to space filling and excavation, the working process of frictional resistance and force model of pile would be changed. Due to the influence of filling, the normal stress of pile-soil interface will increase, and the ultimate bearing capacity of pile will increase. Due to the influence of excavation, the normal stress of pile-soil interface and the ultimate bearing capacity of pile will decrease. There will be considerable tensile force in pile, which could make the pile crack or break.(3) According to different controling standards, such as absolute non-cracks principle, general non-cracks principle and limit state, the tensile strength of pipe pile should be chosed, and the strength loss of steel connectors should be considered.(4) The node strengthes of pipe pile include the tensile strengthes of filling concrete, weld, end plate and steel connector. The end plate and steel connector are weak parts, which should be controled strictly. (5) Engineering practices of prestressed concrete uplift pipe piles in soft soil shown that prestressed concrete pipe piles have the characters of crack resistance, faste construction speed and cheapness. If the weak parts were controled and the bad influences of piping soil compaction and excavation, using prestressed concrete pipe pile as uplift pile is suitable.