大直径扩底灌注桩单桩竖向承载力优化设计

Optimized Design of Vertical Load Carrying Capacity of Single Pile with Large Diameter Expanded Bottom Infill Pile

深基础是以下部坚实土层或岩层作为持力层的基础,其埋深较大。必须在确保建筑物安全的情况下,节约用料,方便施工,且可提升经济效益。为了探究大直径灌注桩作为深基础的构件在承担上部荷载的条件下,其单桩竖向承载力的发挥情况,研究在同种地层沉积条件下,将大直径灌注桩分为同直径不同桩长、扩底式不同桩长两种情况,并按JGJ/T 225—2010《大直径扩底灌注桩技术规程》进行了计算、对比与优化,确认了定型原则,提出了合理的建议与结论。结果表明:桩身几何尺寸较短时不必进行扩底,桩身几何尺寸超过一定长度后可以进行扩底,扩底后的单桩竖向承载力会有相应的提升。扩底会出现几何长度不变但能够发挥桩侧阻力的有效长度缩短的现象。同时,桩扩底施工是否能够成功不同程度地受到地层条件与水文地质条件的制约。

As a foundation with a large burial depth and a solid soil or rock layer below as the bearing layer,deep foundation must save materials and facilitate construction while ensuring the safety of the building and striving to enhance economic efficiency.In order to investigate the performance of the vertical bearing capacity of the single pile of large diameter infill pile as a member of deep foundation under the condition of bearing the upper load,the study divides the large diameter infill pile into two cases of different pile lengths of the same diameter and different pile lengths of expanded bottom type under the deposition condition of the same stratum,and carries out the calculation,comparison and optimization according to the current relevant codes,confirms the sizing principle,and puts forward reasonable suggestions and conclusions.The results show that it is not necessary to expand the bottom when the pile geometry is short,and it is possible to expand the bottom after the pile geometry exceeds a certain length,and the vertical bearing capacity of the single pile after the expansion will be improved accordingly.The bottom expansion will appear the geometric length of the same but can play the pile side resistance to shorten the effective length of the phenomenon.At the same time,the success of pile bottom expansion construction is subject to the constraints of stratigraphic conditions and hydrogeological conditions to varying degrees.