Theoretical Analysis And Experimental Studies On Residual Stress Of Jacked Open-ended Concrete Pipe Piles

Jacked open-ended concrete pipe pile is one of the most commonly used pile foundations nowadays, and residual stress is one of the most important construction effects of such pipe piles. The residual forces in this article are compressive stress in a pile caused during pile penetration result from elastic compression of the pile material which can result to different initial stress in a pile before used and differences on analysis of pile bearing capacity. A systematically research program, involving theoretical analytical calculation, in-situ test and FEA, was conducted to study the properties of residual stress in jacked open-ended concrete pipe piles. Main resarch works and achievements are as follows:(1) Based on energy balance formulation, an expression of residual stress for jacked open-ended pipe pile is resolved considering the soil plug with a series of theoretical analysis. Then the influences of characters for pile and soil as well as cyclic loading on residual stress are researched according to the results of the theoretical calculations.(2) A series of in-situ tests using reinforcement meres and auto DA machine was conducted on jacked open-ended concrete pipe piles to study the residual stress. The tests’results show the maximum residual stress in pile after a static load test is27%of the stress during the load test, which fits the theoretical calculation well. In addition, the depth of the neutral point is77%of the pile length. The tests also reveal the distribution of side friction, residual side friction and residual stress in pile under cyclic loading. The laws of degradation are similar between side friction and residual side friction which present exponential type. The researches indicated that the toe resistance and shaft resistance under the neutral point would be under-interpreted while the shaft resistance above the neutral point was over-interpreted in pile load tests if the residual stress was ignored.(3) The stress and side friction of open-ended pipe pile are studied with FEA during loading process and after unloading, meanwhile some influencing parameters are also discussed.