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复合桩基在达到整体极限承载状态时,因桩的“遮拦作用”使得地基极限承载力较天然地基有一定提高。其分析可简化为地基竖向极限承载力和地基土水平向绕桩作用产生的极限承载力提高值的叠加。利用下限有限元方法,求解得到地基的极限承载力和不同深度处土体绕桩阻力的数值解,并建立了绕桩阻力计算公式。绕桩阻力系数ks随桩间距的增加而逐渐减小。地基极限承载力提高值Δfu随桩间距的增加而逐渐降低。计算表明:复合桩基下绕桩阻力存在并不可忽视,承台下地基极限承载力有明确的提高,可以作为地基的安全储备。
When the composite pile foundation reaches the overall ultimate load state, the ultimate bearing capacity of the foundation increases more than the natural foundation due to the “obstruction effect” of the pile. The analysis can be simplified to the superposition of the ultimate bearing capacity of the foundations and the increase of the ultimate bearing capacity of the subsoil due to the action of the pile in the horizontal direction. The finite element method of the lower bound is used to solve the ultimate bearing capacity of the foundation and the numerical solution of the resistance of the soil around the pile at different depths. The calculation formula of the resistance of the winding pile is established. The resistance coefficient ks around the pile gradually decreases with the increase of pile spacing. The increase of ultimate bearing capacity of foundation, Δfu, decreases with the increase of pile spacing. The calculation results show that the resistance of the composite pile around the pile is not negligible, and the ultimate bearing capacity of the foundation under the pile cap is clearly increased, which can be used as the safety reserve of foundation.