【作者】 张军；

【导师】 郑俊杰；

【作者基本信息】 华中科技大学 ， 岩土工程， 2012， 博士

【摘要】 随着我国经济的飞速发展，对交通运输资源的需求日益增大，高速公路和高速铁路得到了大力发展。在高速公路和高速铁路建设中，不可避免地要穿过一些不适宜修建路堤的不良地基（高压缩性土、淤泥质黏土和泥炭土等）。桩承式加筋路堤具有工期短和成本低的优点，目前已广泛应用于上述基础建设工程。但是，随着桩承式加筋路堤工程应用的增多，发现其应用于工程中仍存在一些不足，包括路堤沉降、不均匀沉降和侧向位移过大，整体或局部路堤失稳以及筋材效率低等。针对桩承式加筋路堤传统技术的不足，研发出了一种新型地基处理技术——桩承式加筋路堤挂网技术。本文从理论研究、试验研究和数值模拟三个方面对挂网技术作用机理进行了系统研究，主要研究内容包括：（1）针对传统技术应用于工程中的上述不足，研发出了桩承式加筋路堤挂网技术，提出了该技术的具体施工步骤，并对其作用机理进行了定性分析。采用有限元法和两阶段法对挂网技术作用机理进行了深入研究，研究结果表明挂网技术可有效减小路堤沉降、差异沉降和侧向位移，提高桩体荷载传递效率。（2）为了减缓路桥过渡段差异沉降，本文提出了一种包括挂网技术、传统技术和加筋技术的联合地基处理方法，并应用于长安高速公路山西境内MCK40+826大桥东侧路桥过渡段。通过现场试验对桩承式加筋路堤挂网技术与传统技术进行了对比分析，研究了随着路堤荷载的增加两种工况下地基沉降、侧向位移、筋材上下表面土压力以及筋材变形的变化规律。试验结果表明：随着路堤填筑高度的增加，传统技术工况下路堤沉降和侧向位移增幅明显大于挂网技术；相对于传统技术，挂网技术工况下土拱效应对荷载传递的贡献略有减小，但张拉膜效应对荷载传递的贡献显著增大。（3）针对桩承式加筋路堤挂网技术受力特性，提出了筋材设计验算简化方法。同时，分析了挂网技术中筋材—桩体—桩间土在路堤荷载作用下荷载传递机理。根据位移和应力连续条件，将路堤填料和加固区视为整体考虑，将筋材视为具有一定刚度的薄板，基于大挠度薄板理论模拟筋材的挠曲变形，并考虑了土拱效应和桩土相互作用，建立了路堤荷载作用下桩承式加筋路堤挂网技术桩帽和桩梁两种工况下受力模型。同时，考虑到加固区土层分布的复杂性，采用有限差分法进行编程计算，提出了挂网技术的理论计算方法。研究结果表明本文方法的计算结果与现场试验监测数据较为接近，证明了本文计算方法的合理性。（4）通过数值模拟分析了桩承式加筋路堤挂网技术的工作特性。挂网技术建模时，筋材与桩在桩顶处共结点模拟固定连接体系，通过对比分析数值模拟计算结果与现场试验监测数据，证明了数值建模的合理性。同时，研究了挂网技术中不同地基土弹性模量、不同筋材抗拉刚度、不同桩长、不同桩间距、不同桩体弹性模量和不同交通荷载条件下的作用机理和工作特性。最后，基于数值模拟结果对挂网技术与传统技术两种工况下工程成本进行了对比分析。研究结果表明：相对于传统技术，挂网技术能有效减小路堤沉降，提高路堤稳定性，作用效果明显，经济效益显著。（5）通过建立二维流固耦合模型，系统分析了挂网技术中路堤沉降、差异沉降、侧向位移、筋材轴力和超孔隙水压力随时间的变化规律。最后，对挂网技术中筋材抗拉刚度、软黏土弹性模量、桩墙间距、桩墙弹性模量和桩墙宽度等重要设计参数进行了参数分析。数值模拟结果表明：路堤填筑完毕时，传统技术工况下超孔隙水压力明显大于挂网技术；相对于传统技术，挂网技术可有效减小路堤工后沉降、差异沉降和侧向位移，提高路堤稳定性；施工过程中，桩墙间距和桩墙弹性模量对挂网技术中各评价指标的影响较大，参数影响等级为中到高级；运营过程中，软黏土弹性模量、桩墙间距和桩墙弹性模量对挂网技术中各评价指标均有显著影响。更多还原

【Abstract】 With the rapid economical development, China has undergone a massivedevelopment in transportation infrastructure in recent years. Many highways andrailways have been constructed. However, weak ground soils (for example, highlycompressible soft soil, alluvial clay, peat, etc) are inevitably encountered in engineeringpractice. Geosynthetic-reinforced and pile-supported (GRPS) embankment is wildly usedin the above-mentioned infrastructures due to its short construction period and low costs.However, with increasing application of the conventional technique of GRPSembankment (named CT embankment), many problems are exposed (i.e., intolerabletotal or differential settlements, large lateral displacement, global or local instability, lowefficiency of geosynthetic, etc). To solve these problems, a new ground improvementtechnique referred to as the fixed geosynthetic technique of GRPS embankment (namedFGT embankment) is proposed. For further and better understanding this new technique,the theoretical analysis, field test and numerical analysis are employed to study theperformance of FGT embankment in this dissertation, respectively, and the main contentsare presented as follows:(1) In view of those deficiencies of CT embankment, the FGT embankment isdeveloped in this study. The principles and construction techniques involved in the FGTembankment are described firstly. Then, the numerical analysis method and two-stageanalysis method are used to study the performance of FGT embankment, respectively.The results show that the FGT embankment can reduce the total and differentialsettlements, and promote efficient load transfer from the subsoil to piles significantly.(2) To distribute the differential settlement between a bridge and adjacent backfillembankment over a longer transition zone, three techniques (a) the FGT embankment,(b)the CT embankment, and (c) geosynthetic-reinforced embankment without piles are usedat the same trial bridge approach site, which is located at the east of MCK+826No.0Bridge in Shanxi Province, the central region of China. The variation of the settlements,the lateral displacements, the pressures at the top and bottom of the geosynthetic layer and the strains of the geosynthetic layer with the increase of the embankment heightbetween the FGT and CT embankments are investigated by field tests. The results showthat the settlements and lateral displacements in the CT embankment are larger than thosein the FGT embankment. The differences of settlement and lateral displacement betweenthe FGT and CT embankments tend to be greater with an increase of the embankmentheight. In the FGT embankment, the soil arching effect is slightly weakened and the loadtransferred through the soil arching effect is reduced. The FGT embankment promotes ahigher tensioned membrane effect and the load transferred through the tensionedmembrane effect is increased significantly.(3) Based on the discussion about the mechanical characteristics of FGTembankment, a simplified check method of the requirement of geosynthetic tensilestrength is proposed. Then, the load transfer mechanism of geosynthetic, pile and subsoilunder the embankment load is analyzed. The embankment and improved area are treatedas a whole with continuous displacement and stress. The geosynthetic is modeled as athin plate and the deformation is calculated by the thin plate theory. The soil arching inthe embankment and the interaction between pile and soil are also considered. Amechanical model of FGT embankment is proposed. Two conditions, the pile cap andpile beam conditions are considered in the mechanical model. The finite differencemethod is used to solve the mechanical model owing to the complexity of the soil strata.Then, the numerical procedure is programmed. Finally, a field test is conducted to verifythe mechanical model and the calculated results are in good agreement with fieldmeasured data.(4) The numerical analysis is performed to investigate the performance of FGTembankment. In the FGT embankment, the geosynthetic and pile are treated as conode atthe top of pile to model the fixing system. The model calibration is conducted to ensure agood representation of the numerical modeling for the embankment application. Aparametric analysis on the influencing factors is conducted to investigate the performanceof FGT embankment, which include the elastic modulus of soil, tensile stiffness of geosynthetic, pile length, pile spacing, pile elastic modulus and traffic load. Based on thenumerical results, the cost evaluation between the FGT and CT embankments is alsocompared. The results show that the FGT embankment can reduce the settlement,enhance the stability and be a more economical and effective scheme for theembankment construction.(5) A two-dimensional numerical simulation by coupled mechanical and hydraulicmodeling is conducted to investigate the time-dependent behaviors of FGT embankmentincluding the settlement, differential settlement, lateral displacement, geosynthetictension, excess pore water pressure, etc. A sensitivity analysis is performed to discuss theinfluencing factors such as tensile stiffness of geosynthetic, pile wall spacing, elasticmodulus of soft clay, elastic modulus of pile wall and pile wall width. The results showthat the excess pore water pressure at the end of construction in the CT embankment ismuch larger than that in the FGT embankment. In comparison with CT embankment, theFGT embankment can sufficiently reduce the post-construction settlement, differentialsettlement and lateral displacement, and enhance the stability of embankment during thepost-construction period. During the construction period, the pile wall spacing and elasticmodulus of pile wall have medium to high influences on the performance of FGTembankment. During the post-construction period, the elastic modulus of soft clay, pilewall spacing and elastic modulus of pile wall have high influences on the performance ofFGT embankment.更多还原