超长钻孔灌注桩群桩效应系数研究

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

应力叠加理论的群桩效应系数公式理论性较强,考虑了桩长、桩距、桩的排列、以及桩间土性质等多种因素的影响。基于应力叠加理论,通过多种工况的算例,定量地分析超长大直径钻孔灌注群桩中桩数、桩间距、桩长以及桩径与群桩效应系数的关系。计算表明:桩数的增加、桩间距的减小、桩长的增加、以及桩径的增大都使得群桩效应系数减小,但它们各自影响的程度不一样,当桩数超过10×10后,桩数的变化对群桩效应系数的影响非常微小;对于超长桩,一般要求桩间距达到10D左右可不计群桩效应的影响;桩长L<50D时,衰减较快,当桩长L>50D时,衰减较慢。最后通过进行8组超长群桩(1、2、4、9桩多种桩群和多种桩距、桩径)的大比例尺现场模型试验,验证应力叠加的群桩效应系数公式的适用性,可为超长钻孔灌注桩设计提供参考。

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.