考虑承台效应的某高层建筑复合桩基设计

Design of composite pile foundation of a high-rise building considering pile cap effect

在高层建筑的地基基础设计中,当基底以下土层不能满足对上部结构的直接承载要求时,经常采用桩基础的形式。但当地基受力层范围内无非密实新填土、液化土、湿陷性土、高灵敏度软土、欠固结土时,桩与承台共同分担荷载是一种客观的现象,如能采取措施避免因外界条件的变化而出现土与承台脱空的现象,使桩间土能够始终保持同承台协同工作,按复合桩基进行设计将能够充分发挥地基的承载能力,节约资源、降低造价。但在实际工程中如不经过认真分析,在土与桩各自承载时容易较高地估计承台底土的荷载分担比例。部分地基基础设计软件中也可输入此类荷载分担比例系数,但应认真分析后再取用,否则主观人为的成分较大,缺乏取用的依据。本文通过对某高层剪力墙住宅考虑承台效应的复合桩基设计过程的梳理,总结了按规范进行复合桩基设计的经验及设计过程中需要注意的问题,并可反推出按复合桩基进行设计时,土与桩各自承载的荷载分担比例。

In the foundation design of high-rise buildings,pile foundation is often adopted when the soil layer below the basement cannot meet the direct bearing requirements of the superstructure.However,it is an objective phenomenon that the pile and the cap share load if there is no dense new fill,liquefied soil,collapsible soil,high sensitivity soft soil and under consolidated soil in the range of foundation stress layer.If measures can be taken to avoid the void of soil and cap due to the change of external conditions,the soil between piles can always work together with the cap,so that the design according to the composite pile foundation will give full play to the bearing capacity of the foundation,save resources and reduce the cost.However,without careful analysis in practical engineering,it is easy to overestimate the load sharing ratio of the bottom soil of the cap when the soil and the pile are loaded respectively.This kind of load sharing ratio coefficient can also be input into some foundation design software,but it can only be used after careful analysis,otherwise it may lack the basis for use due to being subjective and artificial.By combing the design process of composite pile foundation considering the pile cap effect in a high-rise shear wall residence,this paper summarizes the experience of composite pile foundation design according to the code and the problems requiring attention in the design process,and deduces the respective load sharing ratio of soil and pile when designing according to the composite pile foundation.