【作者】 牛建东；

【导师】 刘宝琛； 徐林荣；

【作者基本信息】 中南大学 ， 道路与铁道工程， 2006， 博士

【摘要】 在软基上修建高速铁(公)路需要解决工后沉降控制和提高施工速度两大技术难题。桩-网复合地基的推出为解决稳定性和工后沉降控制这两大技术难题提供了新的途径。目前该方法在工程上已经有-定应用并取得较好的效果，但研究偏少。为此铁道部在京沪高速铁路进行了由一家设计院、两个工程局和三所高校共同参与的软土地基路桥设计参数特大型试验。本文以此高速铁路软土路堤昆山试验段为工程背景，对地基沉降、孔隙水压力、桩土应力比以及土工格栅应力、应变等项目进行系统测试、分析与总结，并在现场试验的基础上利用数值计算方法对桩-网复合地基的承载机理，稳定性及沉降规律进行研究，获取如下主要结论：(1)现场测试确定桩-网复合地基现场测试项目、测试元器件的埋设方案、现场数据采集方案及测试频率；总结出一套针对高速铁路桩-网复合地基试验路堤的元器件埋设、测试方法及数据整理的方法并获得丰富、可信的现场实测资料，可供类似工程项目参考。(2)测试分析成果基于地表沉降、分层沉降、剖面沉降和侧向变形的观测数据得到桩-网复合地基的沉降和变形规律；基于孔隙水压力消散数据获得桩-网复合地基中地基土的固结特性；通过基底应力、桩-土应力比和加筋垫层中土工格栅应力应变的观测数据得到桩-网复合地基的承载机理和荷载传递机理。(3)性状分析针对桩-网复合地基中采用的不同桩型，提出了各自适合的平面应变等效方法；对于砂桩，桩体刚度采用面积等效方法，加固区地基土层水平向渗透系数必须进行等效计算；对于搅拌桩，桩体刚度采用刚度等效的方法。确定了数值模拟中地基土、筋材、筋-土和桩-土界面所采用的数值模型及各模型所需计算参数。通过模型效验，验证计算模型及参数正确。得到了桩-网复合地基加筋垫层中筋材拉力、界面剪应力和界面相对位移的变化及参数影响规律。利用有限元强度折减法可以有效地解决桩-网复合地基稳定性分析问题，得到桩-网复合地基整个填筑过程安全系数变化规律、桩-网复合地基破坏机理及各组成部分对稳定性的影响规律，确定桩-网复合地基可以有效的改善路堤稳定性，提高填筑速率，缩短工期。通过数值计算，对桩．网复合地基沉降规律进行研究，得到桩-网复合地基中地基土参数、桩长、桩体模量、桩的置换率、垫层弹性模量和筋材刚度等参数对总沉降量、加固区压缩量、下卧层沉降量及工后沉降的影响规律。确定桩-网复合地基中提高桩长、桩体模量及增加桩的置换率均可有效地减小和控制工后沉降，这些参数均存在临界值，超过参数临界值后再增加各参数量值，对控制工后沉降的作用有限。(4)设计方法基于实测数据和加筋垫层及稳定性计算结果，确定桩-网复合地基加筋垫层的设计参数——筋材抗拉刚度、筋材抗拉强度、加筋层数及筋土界面系数的取值范围和方法。根据沉降修正系数法，提出了桩-网复合地基沉降的计算方法，确定桩的设计参数——桩长、桩体模量、桩间距和桩径。根据以上结果，得到桩-网复合地基设计方法和步骤。更多还原

【Abstract】 Residual settlement control and construction speed improvement are two technology difficulties if high speed railway and express road are built in soft soil. There emerged Pile-net Composite foundation, which a new way to solve stability and residual settlement control, and it is used in construction with effective performance but less theoretical research.Therefore, China National Railway Ministry made The Design Parameters for Railway and Bridge on Soft Ground Project, which responsible by The Fourth Survey and Design Institute from Ministry of Railways and Tongji University、Central South University、Shouthwest Jiaotong University, China Tie’Er’Shiju Civil Engineering Group Co., Ltd and China Tiesiju Civil Engineering Group Co., Ltd worked together. With In-situ test of Kunshanhigh-speed railway trial embankment, pile-net composite foundation have been careful studied in settlement and lateral displacement and contact pressure and pile-soil stress ratio and the stress and strain of geo-net aspects. Based on the above research, numerical calculation of Pile-net composite foundation, bearing mechanism, stability calculation and settlement law were made advanced research by test. The main conclusions of this paper are as follow:(1) In-situ testIn-situ monitor program, gauges burying schemes, in suit data connection and test frequency were confirmed, which obtained a series of in suit survey information and provide reference for similar constructions in future.(2) Test resultBased on the in-situ data, settlement and deformation of Pile-net composite foundation were studied from surface and magnetic settlement, the settlement profiles across the embankment aspects. Soil consolidation of Pile-net composite foundation was studied by Excess pore pressure dissipation data. Based on soil stress and pile soil stress ratio data, bearing and load mechanism of Pile-net composite foundation were studied and embankment fill, reinforced cushion and soil interaction were researched as well.(3) Properties of Pile-Net Composition FoundationAs far as sand pile and deep mixing pile are concerned, pile modulu and plane strain hydraulic conductivity were calculated and the finite element model was build up and every parameter was confirmed. In-situ results were compared with calculated results. Sand pile stiffness used area equivalent method, and horizontal permeability of reinforced foundation must make matching calculation, and deep mixing pile stiffness used elastic modulus equivalent method. Numerical model and calculation parameters of soft soil of foundation, reinforcement, reinforcement-soil interface and pile-soil interface are confirmed, which proved to be correct. Reinforcement axial forces, interface shear stress and interface relative displacement changes in reinforced cushion of Pile-net composite foundation were researched and parameter effect was studied as well.Safety parameters in every filling stages of Pile-net composite foundation construction were studied by Strength Reduction of the finite element model. Failure mechanics of Pile-net composite foundation and every parts effect on foundation stability were researched.Pile-net composite foundation settlement was studied by the finite element model, as well as how every parameter of foundation Pile, reinforced cushion and reinforcement effect settlement, composite foundation settlement, underlying soil layer post construction settlement and post construction settlement(4) Design MethodRange and method of reinforcement tensile stiffness, reinforcement tensile stress, reinforcement layer and interface coefficient are confirmed by test data and calculation results, which are design parameters of Pile-net composite foundation. Pile length, pile modulu, pile distances and pile diameters are confirmed by correction factor settlement as well as calculation methods. Therefore, calculation methods and steps of Pile-net composite foundation are clarified.更多还原