地下增层开挖托换桩的屈曲稳定临界荷载分析

Buckling stability analysis on critical load of underpinning pile for excavation beneath existing building

为了研究既有建筑物地下室增层开挖对托换桩基础屈曲稳定的影响,提出托换桩桩身屈曲失稳临界荷载及稳定计算长度的理论计算方法.以甘水巷3号组团地下室建设工程为背景,结合Winkler弹性地基梁理论建立托换桩的桩-土体系总势能方程,利用最小势能原理,导得托换桩屈曲失稳临界荷载及稳定计算长度表达式,并分析托换桩屈曲临界荷载影响因素.结果表明:随着半波数的增加,托换桩的临界荷载逐渐收敛;桩侧摩阻力及桩身自重对托换桩的临界荷载影响不明显;托换桩的临界荷载随开挖深度的增大而急剧减小,随桩身直径的增加而逐渐增大;当开挖深度大于4m时,土体水平反力比例系数对托换桩临界荷载的影响可忽略不计.

A theoretical analysis was carried out to estimate the critical bucking capacity and the effective length of the underpinning pile.The influence of excavation beneath existing building on the buckling stability of underpinning pile was studied by the No.3subsection of the Ganshuixiang construction project.The total potential energy of the pile-soil system was determined by employing the Winkler's elastic beam theory.The expressions of critical buckling capacity and effective length of underpinning pile were deduced by using the minimum potential energy principle.The influence factors on the critical buckling capacity of underpinning pile were analyzed.Results indicate that,the critical buckling capacity of underpinning pile converges with the half-wave number increasing;the shaft resistance and the selfweight of pile impose little effect on the buckling load of pile shaft;the critical buckling capacity decreases rapidly with excavation depth increasing but increases steadily with pile diameter increasing.Furthermore,the proportional coefficient of horizontal reaction force imposes insignificant effect on the buckling load when the excavation depth exceeds 4m.