自80年中期以来，复合地基一直是我国地基处理最广泛应用的方法之一。当复合地基采用强度、压缩性均与被加固土体有较大差异的柱状加固体并在加固区形成了显著的非均质和各向异性时，不同基础宽度与深度基础下复合地基复杂的破坏模式和破坏机理、基础宽度与埋置深度对复合地基极限承载力的影响规律一直没有得到深入研究，导致考虑基础宽度和埋置深度影响的复合地基极限承载力理论一直未建立。因此，我国地基基础、地基处理相关规范一直采取了不考虑基础宽度影响、最低程度考虑基础埋置深度影响的保守方法，并众所周知地导致了复合地基承载力被不同程度低估。拟采取理论解析与数值分析、模型试验、离心机试验等，研究不同基础宽度、埋置深度下复合地基中加固体破坏模式及复合地基整体破坏机理、破坏模式、破坏面特征及极限承载力，提出复合地基破坏模式、破坏面特征的系统分类，建立考虑基础宽度和埋置深度影响的复合地基极限承载力理论计算方法与简化方法。

Composite ground has been one of the most extensively used ground improvement methods since mid-1980's. When columns with comparatively high strength and stiffness are adopted to reinforce the soft ground, the reinforced zone of soil with column type reinforcement elements exhibits significant heterogeneous and anisotropy behavior because that the strength and stiffness of column body are significantly different with that of native soil. The failure modes, failure mechanism and ultimate bearing capacity of composite ground under rigid foundation slab considering the effect of width and embedded depth of foundation slab have not been investigated. This leads to that the theory of composite ground ultimate bearing capacity taking into account the effect of foundation slab width and embedded depth has not been built up. Consequently, the simplified method available in the main technical codes regarding the design of ground improvement only consider the effect of embedded depth but doesn't take into account the effect of width of foundation slab. This has been well recognized to lead to the under-estimate the ultimate bearing capacity of composite ground to some extent. Theoretical and numerical analysis, model tests and centrifuge tests are to be performed to study the failure mechanism, failure modes, slip surface and ultimate bearing capacity of composite ground and the effect of width and embedded depth of foundation slab. The failure modes and slip surface will be systematically classified. Finally, the theoretical and simplified methods of ultimate bearing capacity of composite ground are expected to be suggested.