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| Model Test Research on the Negative Skin Friction of Single Pile under Different Loading Sequences |
| MA Xue-ning, ZHANG Pei-yun, WANG Xu, JIA Xi-cui |
| (Lanzhou Jiaotong University, Lanzhou, Gansu 730070,China) |
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Abstract Abstract：Research purposes： The pile negative friction leads to the drop load on pile, which increases the axial force and end resistance of the pile and even leads to pile failure. Because of the different settlement development process of the soil around the pile and the pile, the sequence of the pile loading and the surcharge loading must have a great influence on the negative friction of the pile. In this paper, through model tests, the effects of the sequence of the pile load and the surcharge loading on negative friction of single pile under the condition of different bearing stratum at pile-end were studied. Research conclusions： (1)On the condition of pile -surcharge loading sequences, after the applying of the surcharge load, the neutral point is furthest away from pile top; With the increase of pile load, the position of neutral point is gradually moved up, eventually, the neutral point positions of loess and coarse sand bearing stratum are 0.49l and 0.56 l far from pile top, the axial force of the pile increases first and then decreases, the exert coefficient of bearing capacity of single pile is 0.69 and 0.57, respectively. (2)On the condition of surcharge-pile loading sequences, when first applying pile load, axial force of the pile gradually decreases along the depth, no neutral point, then while applying surcharge load, the axial force increases first and then decreases, and the neutral point appears and gradually moves down, finally the neutral point position of the loess and the coarse sand bearing layer is near 0.41l and 0.50l, and the exert coefficients of bearing capacity of single pile are 0.86 and 0.69, respectively. (3) Under the same bearing stratum, there is the greater exert coefficient of bearing capacity at the pile-surcharge loading sequence, the safety reserve of the bearing capacity of the pile is smaller. (4)In practical engineering, comprehensive analysis of geological conditions, stress characteristics and bearing requirements of the pile foundation should be conducted and appropriate loading sequence should be selected to reduce the friction of pile. (5)The research results can provide a reference for design of pile foundation under the surcharge loading.
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Received: 17 May 2017
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2017, Vol. 34 
