既有高层建筑地下增层开挖桩端阻力损失

Pile base resistance loss for excavation beneath existing high-rise building

针对既有高层建筑地下增层开挖引起原基础底板下桩基承载力损失的问题,在嵌岩桩极限端阻计算公式的基础上,分别应用简化公式以及Mindlin应力解考虑开挖引起的附加应力,计算开挖后极限端阻损失.利用有限元法计算桩端阻力并与理论计算结果进行对比,研究增层开挖条件下桩端极限阻力损失比随不同增层开挖宽度和深度的变化规律,分析桩端参数对桩端阻力损失比的影响.结果表明:损失比随增层开挖宽度的增大而增大,开始增大较快然后变缓并趋于稳定;损失比随增层开挖深度的增大而增大,大致呈线性趋势;岩体的质量越好,损失比越小,当组成岩体的岩块强度较高时更明显;随着桩体嵌入基岩深度的增加,损失比先减小后趋于稳定,当岩体质量较好时更明显.

Excavation beneath the existing high-rise building would lead to the loss of pile bearing capacity. The pile ultimate base resistance loss due to the additional stress caused by excavation was obtained based on the calculation formula for rock-socketed piles by using Mindlin~ s stress solution and a simplified method, respectively. The results of theoretical analysis were compared with that of finite element analysis. The relationship between the ultimate base resistance loss ratio and excavation width and depth was analyzed. Parametric studies were conducted to analyze the influencing factors of the loss ratio. Results show that the loss ratio increases with the increase of excavation width and it shows an initial faster increase followed with a slower increase until a constant value. The loss ratio was approximately linear function of excavation depth. The better the quality of the rock mass, the smaller the loss ratio, which is more obvious for higher unconfined compressive strength of the intact rock. With the increasing of embedded depth, the loss ratio decreases gradually to stable values, which is more obvious for better quality rock mass.