刚性荷载下现浇X形桩复合地基极限承载力特性研究

现浇X形桩是通过等截面周边扩大原理，将圆形截面的正拱变为反拱而成的。作为一种新型的异型截面桩，目前对其极限承载力的计算仍采用规范中建议的经验公式。结合南京桥北污水处理厂地基处理工程的现场静载荷试验，应用有限元软件ABAQUS，建立刚性荷载下现浇X形混凝土桩复合地基的模型，模拟不同桩身模量、桩周土模量、桩长、褥垫层厚度和模量等参数下现浇X形混凝土桩复合地基的荷载-沉降关系，从而得出复合地基的极限承载力。结果表明，现浇X形桩单桩复合地基极限承载力比等截面面积的圆形桩单桩复合地基增大20%以上，X形桩4桩梅花形复合地基极限承载力比等截面面积的圆形桩大12.35%。极限承载力随桩身模量、褥垫层模量、桩周土体模量或者桩长的增大而增大，而且在众多影响因素中桩周土体模量对复合地基极限承载力的影响最为明显。

Analysis of ultimate bearing capacity of X-section cast-in-place concrete pile composite foundation under rigid load

Based on the principle of enlarging perimeter with the same section area,X-section cast-in-place concrete pile(abridged XCC pile) is developed by changing the convex of circular-section to concave.As a new special section pile,the ultimate bearing capacity is calculated by empirical formulas in standard.The in-situ static load tests are carried out based on the foundation treatment project in Qiaobei sewage treatment plant in Nanjing.Besides,a finite element model is established to simulate the XCC pile composite foundation under the rigid base by software ABAQUS.The ultimate bearing capacities are discussed considering some factors including elastic modulus of pile,modulus of surrounding soil,pile length,cushion thickness and cushion modulus.The results indicate that XCC single-pile composite foundation can increase the bearing capacity by 20% more than that of traditional pile.The ultimate bearing capacity of XCC four-pile composite foundation can increase the bearing capacity by 12.35% more than that of traditional pile.The ultimate bearing capacity increases with the increase of pile modulus,cushion modulus surrounding soil modulus and pile length.From the factors,the effect of modulus of surrounding soil is most obviously.