Study On Bearing Capacitive Behavior Of Large-diameter Bore Pile In Nanning And Influenced By The Ground Surface Load

In order to accurately determine the ultimate bearing capacity of large-diameter bored pile in mudstone siltstone interbed foundation of an elevated platform engineer-ing in Nanning, static load test is used to research the load-settlement character of pile in interbed foundation. Aiming to accurately predict and evaluate the ultimate bearing capacity of large diameter bored pile while the test pile didn’t reaching ultimate state, function fitting method is used to predict the load-settlement characters and ultimate bearing capacity of test pile, and 3D numerical simulation back analysis is carried to analysis the test pile at the same time, and then extended to pile groups analysis. In order to investigate the influence of test pile subjected to downward load due to the variation of strip uniform load of stack piers during the large-tonnage surcharge pile loading tests,3D nonlinear analyses for test pile of practical engineering for a specific case and two case studies as well. In addition, Aiming at the problem that the large deformation and crack of pile in hard soil dued to large scale ultra high earth filling during the construction period, numerical simulation analysis is carried to investigate and survey the influence of free-unloaded single pile and loaded pile experience the large scale ground surface load in the side of pile and around the pile, respectively. Through the above studies, some conclusions can be drawn:(1) For the problem that how to determine the ultimate bearing capacity of test pile didn’t reaching ultimate state, function fitting method and numerical simulation back analysis can used to predict the load-settlement characters and the ultimate bear-ing capacity of pile; With the compared of load-settlement characters of a pile in 2×2 pile group without pile cap and single isolation pile by numerical simulation analysis, it shows that the elastic settlement of unloaded-free adjacent pile caused by loaded pile dued to the complex pile-soil-pile interaction and reduces the ultimate bearing capaci-ty of pile in pile group with small space.(2) With the increasing of stack weight lifting before the beginning of pile load-ing (the strip uniform load of stack piers was increasing) during the large-tonnage surcharge pile loading tests, the test pile was suffered from dragload and the settle-ment of test pile was increasing, however, this part of settlement was not measured, the exaggerate of pile stiffness is significant in surcharge pile loading tests during the initial stage of loading due to the strip uniform load of stack piers was decreasing. With the pile head loading over Qu/2, the exaggerate effect beginning decreased sig-nificantly and can be neglect while pile head load reaching the ultimate bearing capac-ity. Therefore,the unltimate bearing capacity of test pile influenced by the strip uniform sfacload can be ignored,the surcharge loading tests remain as a reliable method to es-timate the ultimate bearing capacity of pile(3) The dragload of pile was increasing until reach the ultimate value as the in-creasing of large-scale ground surface load, and then the dragload will decrease; With the increasing of surface load, the behavior of additional settlement of pile dued to large-scale ground surface load show approximate linearly increasing; Compared with the case that lateral surface load of pile, the additional settlement of free-unloaded sin-gle pile and loaded pile caused by large-scale ground surface load around pile are consider to be twice as the former, respectively; the additional settlement of loaded pile is larger than free-unloaded single pile while under the same surface load. Influ-enced by pile side ground surface load, the pile was subjected to lateral deformation and deflection and transverse bending moments.The research results of this paper is not only to solve the problem that the ultimate bearing capacity of test pile didn’t reaching ultimate state difficultly to determine ac-curately, but also to evaluate the effect of test pile due to the variation of strip uniform load of stack piers during the surcharge pile loading test and the influence of pile foundation due to the large scale ultra high earth filling during and after the construe- tion, which provides a theoretical supports and has important theory and application value.