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.