Research on Effect Coefficient of Extra-long Large Diameter Bored Pile Groups

In order to study the effect coefficient of extra-long large diameter bored pile groups,five formulas or methods for effect coefficient of pile groups were analyzed.It is found that the formula based on stress superposition fits the calculation of the effect coefficient of extra-long large diameter bored pile groups.The formula takes into the pile length,pile diameter,friction angle of soil layers and stress superposition.The effect coefficients of 2×2 pile groups and 3×3 pile groups were calculated based on the data of the soil layers,pile length and diameter for the pile groups under the fifth main pier in the Sutong Yangtse River Highway Bridges in P.R.China.The calculated theoretical values are compared with those of the centrifugal model test.The calculated ones are lower only by 7.2~12.7 percent.This shows that the formula based on stress superposition for calculating the effect coefficient of extra-long large diameter bored pile groups is reasonable and can serve as a reference to design types of pile groups.