多桩型复合地基作用机理与动力特性研究

对由碎石桩和CFG桩构成的多桩型复合地基的作用机理进行分析,通过数值模拟,对多桩型复合地基的动力特性进行研究,探讨桩型配比、桩径、桩长、CFG桩桩体刚度和碎石桩桩体渗透性等设计参数对多桩型复合地基动力特性的影响。研究结果表明:相同条件下地震期多桩型复合地基的动变形小于碎石桩复合地基而大于CFG桩复合地基,震后沉降量相对较小,在工程设计时碎石桩与CFG桩的桩型配比宜为4∶5;随桩体长度、桩体直径和CFG桩刚度的增加,多桩型复合地基地震期的竖向动变形逐渐减小;随碎石桩桩体渗透性的增加,多桩型复合地基中的超动孔隙水压力减小,震后沉降量降低。

Research on Mechanism and Dynamic Characteristics of CompositeFoundation with Multi-type Piles

To meet the requirements of bearing capacity and anti-liquefaction of liquefiable foundations, the reinforcement of liquefiable soil using CFG piles combined with gravel piles is used in engineering.In this study, a composite foundation with multi-type piles composed of gravel piles and CFG piles was analyzed.In composite foundations with multi-type piles, gravel piles are supplemented piles that are mainly used to accelerate the foundation drainage consolidation.CFG piles are the main piles that undertake greater seismic load and reduce the dynamic pore pressure and post-earthquake settlement of the foundation.A composite foundation with multi-type piles composed of gravel and CFG piles can improve the bearing capacity and liquefaction resistance of a liquefiable foundation.A three dimensional numerical model was established and the dynamic characteristics of a composite foundation with multi-type piles was studied through numerical simulation;the influence of design parameters such as the ratio of pile type, pile diameter, pile length, CFG pile body stiffness, and gravel pile body permeability on dynamic characteristics of a composite foundation with multi-type piles was analyzed.The results show that the dynamic deformation of a composite foundation, including gravel pile composite foundation, CFG pile composite foundation, and composite foundation with multi-type piles is obviously smaller than that of a natural foundation during earthquakes, and the dynamic deformation decreases with increase in the number of CFG piles.When the ratio of gravel piles and CFG piles is 4:5, the dynamic deformation curve of a composite foundation with multi-type piles is close to that of the CFG pile composite foundation and the influence of the increase in the amount of CFG piles on the reduction in the dynamic deformation of the composite foundation is no longer obvious.When the ratio of gravel piles and CFG piles is 4:5, the dynamic pore water pressure of the composite foundation with multi-type piles is relatively small compared to that of the CFG pile composite foundation, and the composite foundation settlement caused by the earthquake is also relatively low.In engineering design, an appropriate ratio of gravel piles to CFG piles is 4:5.The pile diameter, pile length, CFG pile body stiffness, and gravel pile body permeability can affect the dynamic deformation of a composite foundation with multi-type piles.With increase in the pile length, pile diameter, and CFG pile stiffness, the vertical dynamic deformation of the composite foundation with multi-type piles decreases gradually.With the increase of the permeability of the gravel pile body, the excess dynamic pore water pressure in the composite foundation with multi-type piles and the deformation after an earthquake decrease.