变荷载下悬浮TDM桩复合地基固结分析

T形水泥土搅拌（TDM）桩是具有扩大头的变直径搅拌桩，T形水泥土搅拌桩复合地基的固结机理较传统的等直径水泥土搅拌桩复合地基复杂得多，固结计算也更为困难。为了获得悬浮T形水泥土搅拌桩复合地基的固结计算模型，基于加固区桩-土等竖向应变假设，推导出变荷载作用下悬浮T形水泥土搅拌桩复合地基的一维固结控制方程和求解条件。将固结方程和求解条件进行函数变换，利用3层地基一维固结理论建立单级加荷条件下T形水泥土搅拌桩复合地基的固结解析解，包括加固区、桩间土和下卧层土中的平均超静孔隙水压力解答和复合地基整体平均固结度解答。然后，通过与固结度有限元数值计算结果的对比，验证固结解析解的合理性。最后，利用固结度解析解对影响复合地基固结速率的主要因素进行分析，研究悬浮T形水泥土搅拌桩复合地基的固结特性。研究结果表明：复合地基固结度的解析解与有限元数值解较为一致；悬浮T形水泥土搅拌桩复合地基的固结速率随水泥土搅拌桩贯入比、压缩模量、下部小直径搅拌桩的置换率以及下卧层土压缩模量的增加而增大，搅拌桩贯入比、下卧层的刚度对复合地基固结速率的影响更为显著；扩大头尺寸和刚度的变化对T形水泥土搅拌桩复合地基固结速率的影响很小。

Consolidation Analysis of Composite Ground with Floating T-shaped Deep Cement Mixing Columns Under Time-dependent Loading

A T-shaped deep cement mixing (TDM) column with an enlarged head is a variable-diameter column. The consolidation mechanism of composite ground with TDM columns is significantly more complicated than that of composite ground improved by traditional equal diameter deep cement mixing (DCM) columns, and its consolidation calculation is more difficult. To obtain the consolidation calculation method for composite ground with floating TDM columns, based on the equal vertical strain assumption of the TDM column and surrounding soil within the improved zone, the one-dimensional equations governing consolidation and corresponding solution conditions of the composite ground were derived under time-dependent load. By means of the functional transformation of excess pore water pressures, the corresponding consolidation solutions were developed under ramp load using the one-dimensional consolidation theory of three-layer soil ground, including the average excess pore water pressures within the improved zone, surrounding soil, and the underlying stratum, as well as the overall average degree of consolidation of the composite ground. Subsequently, the correctness of the proposed solution was proved by comparing the consolidation rate with the results obtained by the finite element method (FEM). Finally, the main influence factors were analyzed to investigate the consolidation behavior of the composite ground using the proposed analytical solution. The results indicate that the proposed consolidation solutions and FEM results show a good match. The consolidation rate of the composite ground increases with an increase in the penetration ratio and constrained modulus of the TDM column, area replacement ratio of the DCM column beneath the enlarged head, and constrained modulus of the underlying stratum. The most important influence factors are the penetration ratio of the TDM column and underlying stratum stiffness. Changes in the size and stiffness of the enlarged head of the TDM column have an insignificant effect on the consolidation rate of the composite ground.