基坑开挖对邻近单桩影响的改进计算方法

Improved Method of Calculating the Influence of Foundation Pit Excavation on Adjacent Single Pile

在城市建设中,紧邻建筑物桩基进行基坑施工会引起桩基产生附加变形和附加内力,进而会影响到上部建筑物的安全性与适用性.关于该问题的理论研究,目前广泛采用的弹性地基梁法将桩基视为Winkler地基或Pasternak地基中的Euler-Bernoulli梁,未考虑桩基的剪切效应及基坑开挖扰动引起的地基参数沿桩基竖向的不均匀性.文中将既有桩基视为Vlazov地基中的Timoshenko梁,考虑桩基剪切效应及地基参数沿桩基竖向不均匀分布的特性,建立了基坑开挖对邻近单桩力学行为影响分析的两阶段解析方法,与既有研究成果及现场监测数据进行了对比验证,结果表明:该计算方法能够对基坑开挖影响下邻近单桩的力学响应进行准确有效的分析.同时,从地基模型的选择和桩基剪切效应的影响两方面进行了讨论分析,分析表明:Vlazov地基模型参数确定更具理论依据且该模型更符合工程实际;随着桩径的增大桩基剪切效应对桩基内力的影响显著.

The construction of foundation pit adjacent to the pile foundation of a building will cause additional deformation and internal force of the pile foundation,which will affect the safety and applicability of the upper building.In view of the current theoretical research on this problem,the elastic foundation beam method is widely adop- ted,which simplified the pile as an Euler-Bernoulli beam resting on the Winkle foundation or Pasternak foundation.However,this method is unable to account for the shearing effect of the pile and the u0x09nevenness of the soil parameters along the pile caused by excavation.So an improved two-stage analytical method was proposed,seeing existed piles as Timoshenko beams resting on the Vlazov foundation and considering both the bending and shearing effects.The results were compared with the existing research results and field monitoring data.The results show that the calculation method can accurately and effectively analyze the mechanical response of adjacent single pile under the influence of foundation pit excavation.At the same time,the selection of foundation model and the influence of shear effect of pile foundation are discussed and analyzed.It is concluded that the parameters determination of Vlazov foundation model has more theoretical basis and the model is more in line with engineering practice;and with the increase of pile diameter,the shear effect of pile foundation has a significant impact on the internal force of pile foundation.