不同围岩强度下大直径嵌岩钻孔灌注桩 承载力尺寸效应的数值模拟

利用数值模拟的方法，通过模拟20种不同工况得到不同岩体和不同直径的大直径嵌岩钻孔灌注桩的桩侧和桩端阻力尺寸效应系数，分析开挖引起的天兴洲大桥直径达3.4 m嵌岩钻孔灌注桩极限承载力尺寸效应问题。结果表明，（1）围岩强度越小，极限端桩阻力和极限摩阻力尺寸效应越大，尺寸效应系数越小。当围岩强度为1～5 MPa时，围岩在开挖过程中破坏明显，尺寸效应显著；当围岩强度大于10 MPa 时，围岩破坏不明显，尺寸效应明显减弱；（2）相同围岩强度下，桩径越大，极限端桩阻力和极限摩阻力尺寸效应越大，尺寸效应系数越小，相比桩侧阻力，桩端阻力尺寸效应更明显，尺寸效应系数略小。（3）极限端桩阻力和极限摩阻力尺寸效应系数与直径成双曲线函数关系。

Numerical simulation of size effect on bearing capacity of large diameter rock-socketed piles under different strengths of surrounding rocks

The size effect coefficients of side and tip resistance of large diameter rock-socketed pile under 20 different conditions are obtained by using FLAC3D. The size effect on ultimate bearing capacity of rock-socketed bored piles with diameters of up to 3.4 m for Tainxingzhou Bridge caused by the excavation has been analyzed. The results show that: (1) The smaller the surrounding rock strength, the size effect of ultimate end of the pile resistance and ultimate friction resistance become greater, and the smaller the size effect coefficient. When the surrounding rock strength is 1-5 MPa, the damage of surrounding rock during excavation is obvious; the size effect is obvious. When the surrounding rock strength increasing to 10 MPa, the damage of surrounding rock during excavation is not obvious, the size effect is significantly weakened. (2) Under the same rock strength, the larger the pile diameter, the larger the size effect of the extreme end of the pile resistance and ultimate friction resistance and the smaller the size effect coefficient. Compared with pile side resistance, the size effect is more pronounced and the size effect of tip resistance coefficient is slightly smaller. (3) The relationship between size effect coefficient of ultimate end of the pile resistance and ultimate friction resistance and pile diameter is well fitted with the hyperbolic function.