混凝土芯砂石桩复合地基双层荷载传递机理及固结理论研究

The composite foundation with concrete-cored sand-gravel pile, which is composed of the concrete-cored sand-gravel pile, the geosynthetic cushion and the foundation soil, is a new technology with the advantages of the high strength prefabricated concrete pile and the better drainage and consolidation characteristics of the sand-gravel piles.The key point of strength and bearing capacity of the concrete-cored sand-gravel pile composite foundation is the mechanism of the double-layer load transfer between the prefabricated concrete pile and the annular sand pile and that between the annular sand pile and foundation soil.Centrifugal model tests will be conducted to analyse the behavior and mechanism of double-layer load transfer for concrete-cored sand-gravel pile composite foundation. Base on the assumptions the distribution behavior, the distribution of skin friction between the pile and the surrounding soil will be proposed and the settlement calculation method for concrete-cored sand-gravel pile composite foundation , considering the pile-soil interaction, will be proposed.The evolution of the additional stress with depth and time will be studied, and the solution of consolidation problem of composite foundation with annular permeable boundary condition with be derived.The influence of design parameters of composite foundation on the consolidation and settlement will be studied by numerical simulation, and the method for estimating the bearing capacity, total settlement and post-construction settlement will be proposed.Achievement obtained in this study will show the mechanisms of bearing capacity and consolidation characteristic of this new composite foundation, and will possess the referential value for the theorical and practical researchs on new techniques in foundation engineering.

混凝土芯砂石桩复合地基由竖向混凝土芯砂石桩、水平砂石垫层和地基土共同组成，能同时发挥预制混凝土芯桩强度高及砂石桩加快软土排水固结这两方面的技术优势。研究混凝土芯砂石桩复合地基受力与变形特性的关键是揭示混凝土芯桩与砂桩、砂桩与软土之间的双层荷载传递机理。采用土工离心模型试验方法分析复合地基工作性状，揭示混凝土芯砂石桩复合地基的双层荷载传递机理。基于离心模型试验与现场试验数据，提出桩侧摩阻力分布模式和附加应力随深度与时间变化的模型，建立考虑桩土共同作用的混凝土芯砂石桩复合地基沉降计算理论，推导环形透水边界条件下的复合地基固结解答。通过数值计算，研究复合地基设计参数对固结与沉降的影响，完善混凝土芯砂石桩复合地基承载力、总沉降和工后沉降计算方法。项目在研究手段与理论分析上的创新成果不仅能揭示混凝土芯砂石桩复合地基承载机理和固结特性，而且能为地基与基础工程领

混凝土芯砂石桩复合地基结合了刚性桩复合地基承载力高及砂井地基排水固结快这两个方面的优点。通过模型试验、现场试验、数值分析对混凝土芯砂石桩复合地基的荷载传递和固结特性进行了系统的研究。分析了路堤填筑及预压过程中混凝土芯砂石桩复合地基路堤填土的土拱效应，揭示了混凝土芯砂石桩复合地基的荷载传递机制是路堤填土的土拱效应、加筋体的拉膜效应、环形砂石桩的固结排水效应、桩土相互作用等的耦合作用。设置环形砂石桩加速桩间土的排水固结，加快桩周土超静孔压消散，增大桩土差异沉降，提高路堤填土的土拱效应发挥程度。提出了路堤填土-加筋体-桩-桩间土-下卧层相互协调的土拱效应计算方法，建立了能够考虑路堤填筑与桩间土固结相耦合的桩、土荷载分担计算模型，分析了不同影响因素对土拱效应及复合地基承载力的影响。通过对荷载传递函数模式的修正，建立复合地基沉降计算方法。提出固结计算中根据桩间土分担的荷载来合理地考虑芯桩的应力集中效应，在此基础上建立了考虑应力集中、附加应力变化和环形排水边界的混凝土芯砂石桩复合地基加固区的固结模型，并给出了解析解答。项目研究成果揭示了混凝土芯砂石桩复合地基荷载传递机理和固结特性。