An efficient analytical approach is proposed to calculate the settlement of a long-short-pile composite foundation under vertical loads, without the expense of a full rigorous analysis. The proposed approach is based on the superposition of the displacement of individual pile and soil element. In the superposition calculation,the interaction factors of pile-pile, pile-soil and soil-soil are employed to facilitate the analysis of pile groups subjected to static vertical loads. The paper presents a rigorous analytical method for calculating the interaction factor between two piles of different lengths subjected to vertical loads. Following the technique proposed by Muki and Stemberg.the problem is decomposed into an extended soil mass and two fictitious piles characterized respectively by young's modulus of the soil and that of the difference between the pile and soil. Using the principle of superposition the long-short-pile composite foundation is calculated. The proposed interaction factors of pile-pile and pile-soil can consider the strengthening effect of intervening piles. The validity of the present method has been verified through comparing with other existing solutions. A parametric analysis is made to study the composite foundation settlement and the loads sharing by the individual pile and subsoil. The proposed method could be used to analyze the large composite foundation.%利用桩——桩、桩——土、土——土之间的相互作用系数,通过桩和土单元的位移叠加建立了一种竖向荷载作用下的长短桩复合地基分析方法,该方法不对群桩进行整体分析,因此,计算效率较高.根据Muki和Sternberg的计算方法来分析长短桩间的相互作用系数,该方法将半空间中的两根桩分解为两根虚拟桩和半空间扩展土,其中,虚拟桩的弹性模量等于桩与土的弹性模量之差.本文计算方法得到的相互作用系数可以考虑桩的“加筋效应”.利用叠加原理对长短桩复合地基进行计算分析,通过与已有文献计算结果的比较,验证了本文计算方法的正确性,并对长短桩复合地基的沉降、各桩以及土之间的荷载分担情况进行了参数分析.本文方法能够用来分析大规模长短桩复合地基,具有一定的工程应用前景.
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