交通荷载下桩网复合地基长期变形机制与计算方法研究

There are some problems with too much deformation of expressway or high-speed railway infrastructure on soft soil foundation under traffic load. Especially, the problem of excessive post-construction settlement of composite foundation seriously affects the operation of the infrastructure. The problem has been plaguing the academia and the engineering community. Pile net composite foundation is a widely used method for soft soil foundation treatment. Its deformation calculation method under traffic load cannot consider the effect of traffic load. The calculation method is impossible to predict the long-term deformation of composite foundation. Therefore, there is a need to analyze its deformation mechanics and develop the corresponding calculation method. A variety of measures will be involved in this proposal such as theoretical analysis, indoor test, model test and numerical simulation. The proposal aims to establish the deformation mechanics and propose the deformation calculation method of pile net composite foundation. Firstly, an explicit and implicit coupling long-term cyclic accumulation strain model is established, based on the cyclic elastoviscoplastic constitutive model for clay considering nonlinear kinematic hardening rules and structural degradation that proposed by Kimoto. Then, the pile soil interaction contact model is established based on the test results of pile soil interaction properties under cyclic load. Considering the interaction among pavement, embankment and composite foundation, the long-term deformation law of composite foundation will be gotten and the deformation mechanics of composite foundation is revealed. Finally, the long-term deformation calculation method of pile net composite foundation under traffic load is proposed to accurately predict the long-term deformation of composite foundation. This study not only helps the fine analysis of geotechnical engineering problems, but also provides the theoretical basis and technical support for the safety design of road operation.

交通荷载下软土地区道路基础设施易发生过大变形，特别是复合地基处理路段工后沉降过大问题严重影响设施运营，这一难题一直困扰学术界和工程界。桩网复合地基是一种广泛用于软土地基处理的方法，其变形计算方法不能有效考虑交通荷载的影响，无法预测其长期变形，因此亟待研究其变形机制并研发相应计算方法。拟通过理论分析、室内试验、模型试验和数值模拟等手段，开展交通荷载下桩网复合地基长期变形机制及计算方法研究。首先基于考虑非线性运动硬化和结构退化的循环粘弹塑性本构理论，建立显式和隐式耦合的长期循环应变累积计算模型；再基于循环荷载下桩土界面特性试验结果建立界面接触模型；考虑路面-路基-地基共同作用，揭示复合地基的长期变形规律和变形机制；最后提出大次数交通荷载作用下桩网复合地基长期变形计算方法，实现交通荷载下地基长期变形准确预测。本研究除了实现岩土工程问题的精细分析，还可为道路运营安全设计提供理论依据和技术支撑。

交通荷载下软土地区道路基础设施易发生过大变形，工后沉降过大问题严重影响设施运营，广泛用于实际工程的桩网复合地基长期变形机制有待揭示，预测或计算交通荷载下桩网复合地基长期变形对于道路基础设施的运营具有重要意义和工程应用价值。本项目采用室内模型试验、理论分析及数值模拟等研究方法，开展了交通荷载下桩网复合地基长期变形机制及计算方法研究。（1）基于非线性运动硬化规则和黏弹塑性理论，考虑软黏土结构退化的影响构建了一个关于软黏土的循环黏弹塑性本构模型，可用于长期循环应变累积计算；并通过有限元软件ABAQUS的二次开发平台，构建了一个可用于软黏土在循环荷载作用下动力响应分析的用户材料子程序。（2）研制了侧向增压试验装置，开展了循环荷载下单桩承载变形室内模型试验，研究了其承载变形特性，揭示了循环荷载下桩土相互作用规律，并通过理论分析构建了桩土相互作用模型，分析了桩基动态沉降发展规律。（3）开展了多组循环（交通）荷载下桩网复合地基长期变形室内模型试验，分析了多种因素下的桩网复合地基变形特性，得到了桩网复合地基的长期变形发展变化规律，揭示了交通荷载下复合地基的长期变形机制。（4）提出了大次数交通荷载作用下地基长期变形计算方法及预测方法，分析了相关参数对其长期变形发展的影响及交通荷载下地基长期变形发展特性，初步实现了交通荷载下地基的长期变形预测。本项目研究成果发表论文14篇（SCI、EI检索8篇），并录用SCI刊源期刊论文1篇及中文期刊论文2篇。申请发明专利6项（已公开），授权实用新型专利1项；已培养硕士研究生6人。