交通荷载下筋箍碎石桩复合地基承载变形机理及长期沉降计算方法研究

In recent years, along with the development of the high way construction, it is becoming increasingly necessary to construct infrastructure in districts where were previously considered unsuitable to. Construction of road embankment over soft subsoil can result in failure or large, often differential, settlements on the surface of the embankment. A variety of techniques including some innovative techniques such as the new foundation treatment referred herein concerned with geosynthetic encased stone columns are required to solve these problems. Despite of the many successful field applications, the geosynthetic encased stone column is still not widely used at the same level as those conventional methods such as piling, due to the lack of design procedures. Limited work has been done on the working mechanism of load embankment supported by encased stone columns under traffic loads. Relative analysis methods is lacking as well. The working mechanism of the composite foundation reinforced with geosynthetic encased stone columns under traffic load is going to be studied by indoor model tests, theory and numerical simulations. Many researches will be conducted to study the dynamic characteristics and evolution of several soils, encased stone column and compound stone—soil body, distribution mode of dynamical subsidiary stress and its cycle cumulative effect, and the dynamic consolidation of the composite foundation. .On the base of that, a new long-term cumulative settlement analysis method is proposed by employing time-varying damage mechanics theory. The research of this project will have a contribution to further improving the design theory of this foundation treatment and popularizing its application.

随着我国高速公路的迅猛发展，大量线路需穿越深厚软土地基。如何在较短工期内处治好该类地基，控制工后沉降和不均匀沉降，已成为制约该类地区修筑高速公路的技术难题。在传统碎石桩外设置土工加筋套筒形成的新型筋箍碎石桩复合地基技术为解决此类问题提供了新的有效途径，但其相关研究仍处于初级阶段，特别是对交通循环移动荷载下筋箍碎石桩复合地基的荷载传递机理及其变形特性研究尚缺乏深入系统的研究。本项目拟从土工试验、室内模型试验、数值分析和理论分析三方面入手，深入分析长期循环移动荷载下桩、土及其复合土体动力特性、桩－筋－土界面的循环损坏演化规律，动附加应力传递模式及循环累积规律，复合地基动力固结特性等，研究交通循环移动荷载下筋箍碎石桩复合地基系统的承载变形机理，在此基础上，引入损伤时变分析方法，深入研究循环荷载下筋箍碎石桩复合地基沉降计算方法，以期促进该处治技术及其设计理论的进一步完善，加速其推广应用。

随着我国高速公路的迅猛发展，大量线路需穿越深厚软土地基。如何在较短工期内处治好 该类地基，控制工后沉降和不均匀沉降，已成为制约该类地区修筑高速公路的技术难题。在传统碎石桩外设置土工加筋套筒形成的新型筋箍碎石桩复合地基技术为解决此类问题提供了新的有效途径，但其相关研究仍处于初级阶段，特别是对交通循环移动荷载下筋箍碎石桩复合地基的荷载传递机理及其变形特性研究尚缺乏深入系统的研究。本项目通过试验分析、数值模拟、理论研究等多种途径对交通荷载下筋箍碎石桩复合地基承载变形机理及长期沉降计算方法进行较深入研究。研究主要内容及重要成果如下：.（1）通过室内无侧限压缩试验和颗粒流数值模拟，研究分析了循环荷载下筋箍碎石桩单元体动力响应特性，建立了单元体动力参数与循环次数之间的函数模型，获得累积变形与循环次数的函数关系，桩体动弹性模量、阻尼比与轴向应变的函数关系。.（2）通过室内模型试验及三维离散元-有限差分耦合数值模拟，研究分析了循环荷载下筋箍碎石桩复合地基的荷载-沉降特性、承载变形特性、桩周土孔隙水消散规律等动力响应特性，进而揭示了循环荷载下筋箍碎石桩复合地基承载变形机理。.（3）通过理论分析结合ABAQUS数值模拟，研究分析了土工加筋路堤的路面结构层受力变形特征、加筋垫层变形特性、路堤中动应力传递等动力响应问题。.（4）基于弹性地基上Timoshenko梁理论、双层Euler梁理论等，分别考虑土拱效应、筋土界面摩阻效应、桩土刚度差异、路面结构层刚度、碎石桩的排水固结效应等影响，提出了“筋箍碎石桩+土工加筋垫层”双向增强复合地基沉降计算方法。.（5）基于Kelvin地基上有限长梁理论，获得了交通荷载下黏弹性地基有限长梁的瞬态问题半解析解；在此基础上，建立了移动荷载下土工加筋路堤的改进双层地基梁分析模型，并采用一阶摄动理论获得了相应的内力位移解答，进而揭示了交通荷载作用下的土工加筋路堤的动力响应特性。