置换率是确定CFG桩复合地基的关键指标之一，根据土层分布明确桩长后针对目标附加荷载选择置换率是竖向结构体系决策的基础，目前缺少不同置换率复合地基力学性状附加荷载影响规律共同认知。通过进行2组相同附加荷载和加固深度、不同置换率的复合地基离心模型试验，研究复合地基桩身轴力、桩侧摩阻力、桩土应力比和地基沉降响应附加荷载的分布及变化规律。研究结果表明，因置换率的增大，（1）CFG桩所承受的轴力有所减小，且轴力最大值所在位置上移；（2）摩阻力零点位置和桩体上部负摩阻力最大值位置出现上移且后者变化速率加快，桩端最大正摩阻力值明显减小；（3）桩土应力比有所减小，且在深层土体中其沿深度方向的减小速率变小；（4）地基沉降和地表沉降明显减小，地表沉降与荷载呈线性关系变化，CFG复合地基的复合模量有所提高。

Replacement rate is one of the key indicators for designers to determine the composite foundation of CFG piles. After determining the pile length according to the distribution of soil layer, the choice of replacement rate is the basis of vertical structure system decision-making according to additional load for target. At present, we have a lack of common knowledge and understanding of the mechanical properties of composite foundation affected by additional load under different replacement rates. Two centrifuge model tests with the same additional load and reinforcement depth and different replacement rates have been carried out to study the change law of the pile axial forces, pile side frictional resistances, pile-soil stress ratio and foundation settlement of the composite foundation during loading process. As the increase of the replacement rate, the test results show that: (1) The axial force of CFG pile is reduced; and the position of the maximum axial force is up along the pile. (2) The positions that the direction of pile side frictional resistance changes or that has the maximum negative frictional resistance in the upper part of the pile are also up along the pile; and the rate of change of the latter is reduced. The maximum positive frictional resistance in the lower part of the pile is obviously reduced. (3) The pile-soil stress ratio is reduced and its reduced rate along the depth direction in deep soil is decreased. (4) The foundation settlement and the ground surface settlement are effectively decreased; and the surface settlement changes linearly with the load; and the composite modulus of CFG composite foundation is improved.