Study of pile group effect coefficient for super-long bored piles

The theory of the stress superposition for the pile group effect coefficient formula takes into consideration of,among other factors,pile length,spacing and arrangement,as well as the characteristics of soils between piles.Based on stress superposition theory,a quantitative analysis is conducted for the relationships between the number of piles,pile spacing,pile length of super-long large-diameter bored pile groups and the pile group effect coefficient.The calculations show that the pile group effect coefficient decreases as the number of piles and pile length and diameter increase,and as pile spacing decreases.When the number of piles are more than 10×10,any change in the number of piles has a small effect on the pile group effect coefficient.For long piles,the pile spacing to satisfy the general requirements of about 10D needs not to take the effect of the pile group into account.When the pile length is less than 50D,the effect quickly decreases,whereas when the pile length is larger than 50D,the effect decreases slowly.A large-scale field model static loading test of eight groups of pile is conducted to verify the applicability of the stress superposition pile group effect coefficient formula.