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| INFLUENCE OF LAYERING OF STRATUM UNDER PILE TIP ON PILE LONGITUDINAL STIFFNESS |
| WANG Ning1，WANG Kuihua1，2 |
| (1. MOE Key Laboratory of Soft Soils and Geoenvironmental Engineering，Zhejiang University，Hangzhou，Zhejiang 310058，China；2. Key Creative Team of Disaster Control Engineering of Zhejiang Province，Hangzhou，Zhejiang 310058，China) |
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Abstract In order to identify the influence of the thickness and layering of stratum between the pile tip and bedrock on the pile stiffness and damping，a longitudinal vibration response of single pile was obtained by a taper fictitious soil pile model. The soil in the tapered area of influence，which is extending to the surface of the bedrock，is treated as a fictitious soil pile. The pile complex impedance was obtained by impedance transfer method combining the boundary condition at the fictitious pile tip. A parameter analysis of the stratum under the pile was carried out to determine the effect of the soil under the pile on the complex impedance at both pile tip and head. The results show that，the stiffness of pile has a significant improvement，and the damping decrease，when the stratum between the pile tip and bedrock is less than 5 times the radius of the pile. The soft interlayer in the stratum under the pile will result in the decrease of the pile stiffness and increase of the pile damping；and the hard interlayer has an inverse effect. In addition，for multilayer stratum under the pile tip，a major error of pile complex impedance may be created only considering the first layer，particularly for the pile subjected to quasi-static load.
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Received: 06 August 2012
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2013, Vol. 32 
