【作者】 陈炳初；

【导师】 赵明华；

【作者基本信息】 湖南大学 ， 岩土工程， 2013， 博士

【摘要】 相对于高路堤而言,低路堤具有占地少、造价省,符合科学发展观的特点,近年来越来越受到工程界的亲睐,但当面对一些特殊土地质,尤其在穿越软土地区时,如果不采取有效的软基处理措施,采用低路堤的效果往往会不尽如人意,这是由于低路堤因有限的填土高度无法有效扩散上部荷载,容易引起差异沉降量过大的问题,为解决在软弱土地区内进行低路堤设计中的荷载扩散问题,本文提出将土工格室与其内碎石等填料组成的加筋结构层置于路基上部,构成一种新型的土工格室低路堤-刚性路面结构体系。它综合了土工格室结构层能抗弯抗剪的特点,低路堤在土地资源节约上的优势以及混凝土刚性路面的原材料在我国可以自给自足、更适合重交通量、设计寿命期长等长处,而具备良好的发展潜力,但是对该体系的研究尚在起步阶段。为此,本文结合国家自然科学基金项目“散体材料桩复合地基承载机理及其按变形控制设计理论研究”(项目编号51078138),以理论分析结合有限元数值模拟以及室内模型试验为手段,针对此种新型结构体系的承载机理、沉降两方面开展较为深入、系统的研究,主要工作分为以下几点：(1)通过对国内外已有的相关文献的总结分析,较为全面的梳理有关低路堤结构、路基对交通荷载的响应,以及作为加筋土类中重要一员的土工格室的应用与加固机理的知识,作为对本文提出的新体系进行深入研究的基础性资料。(2)针对土工格室结构层作为下面层的适用性开展了研究,主要分为土工格室结构层的抗弯能力和抗冲刷能力两部分。在研究土工格室结构层的抗弯能力时,通过有限元反分析,定量的建立起弯曲模量与跨中挠度的经验关系,可作为同类型实验的数据处理工作的参考；进一步,设计了6组叠梁试验来研究土工格室结构层的弯曲模量测定及其影响因素,试验结果表明：格室的展开宽度对弯曲模量值有较大的影响,在实际工程中应尽可能的将格室展开至近正菱形。在分析刚性路面下基层的冲刷机理时,认为冲刷现象的内因可归结为积聚于板底的自由水的浸泡软化作用,外因是交通荷载导致的动水压力的反复冲刷作用。而采用土工格室碎石结构层不但可以在刚性路面下形成良好的排水通道,使渗入水分可以及时排出,而且因为土工格室碎石结构层独特的强度与刚度的形成机理,它受到的水的软化作用较小；借鉴土工膜袋防冲刷的成功经验,在土工格室结构层上覆一层透水土工布,可减少动水压力对结构层的直接冲刷作用,保证它的抗冲刷能力。(3)全面地阐述了本文所提出的土工格室低路堤-刚性路面结构体系,说明了软弱土地区的土工格室低路堤-刚性路面结构体系的主要组成部分及各部分的功能,并深入地研究了该结构体系承载特性。利用数值分析软件ADNIA建立起平面应变模型,计算了交通荷载产生的应力与变形在路堤中的扩散问题,证明了土工格室结构层的存在将大大改善混凝土路面板的受力状态,并让路基内部应力更快的衰减。在工程设计实用性计算方面,研究结果表明,可用现行规范中的弹性地基双层板计算模型来分析新体系的路面板临界荷位处的荷载应力。(4)通过有限元模拟计算,定性地比较了路面下有无土工格室结构层时的变形特点,证明了设置土工格室结构层可以有效减小地基表面的差异沉降；而与设置同样厚度同样参数的土工格室垫层于地基表面的情况进行了对比研究时,发现总沉降值在采用土工格室结构层时比以垫层形式置换出软基中的部分软土时明显减小,而在控制差异沉降的表现上两者相当。进一步对可能影响到板间差异沉降的7个因素设计了3个水平的正交试验,对以板间差异沉降为试验指标时进行的极差分析与方差分析都表明,各因素的影响大小顺序为：土工格室结构层厚度>低路堤高度>软基模量>低路堤填土的模量>土工格室结构层模量>路面板厚度>路面板模量,所以要控制好板间差异沉降,最有效的方法是提高土工格室结构层的高度和低路堤的填土高度。(5)基于相似理论,设计并完成了两组具有可比性的室内模型试验,将模型试验中的六个小项分成三个阶段来进行,藉此来比较有无土工格室结构层时两种体系工作性能的差异,以研究土工格室低路堤-刚性路面体系的承载和变形特性。试验中采用加装变速箱的强制式搅拌机驱动将圆周运动转变为往复直线运动的连杆体系,成功的控制了小车运动距离和速度,实现了交通荷载的周期性模拟。试验结果验证了本文提出的土工格室低路堤-刚性路面结构体系的可行性。更多还原

【Abstract】 Recently, the low embankment has been receiving more and more attention for the design of road structures attributed to its advantages, such as economic space occupa-tion and saving construction cost, compared with the high embankment. However, for some special land especially the soft soil area, the low embankment cannot exploit its advangages if effective soft ground treatment measures were not taken. The reason is that the limited filling height of the low embankment cannot diffuse the upper load ef-fectively which easily leads to excessive differential settlement problems. In order to solve the issue of load proliferation for the design of low embankment in soft soil area, this thesis presented a new type of geocell reinforced low embankment-rigid pavement system (GRLERPS) by putting the geocell and its internal gravel packing placed on the top of the embankment. As a new road structure type, the GRLERPS has a good poten-tial for applications, because it combines the high flexural and shearing strength of geocell and land resource-saving of the low embankment, as well as advantages of the concrete rigid pavement, such as readily available raw materials, capability of carring heavy traffic and long design life. But the new system is still in the exploratory re-search stage. In this thesis, an in-depth systematic research on GRLERPS is carried out from two aspects:load bearing mechanism analysis and the settlement analysis, by means of theoretical analysis, model test and finite element analysis. The main work can be clarified as follows:(1) Through the relevant existing literature at home and abroad, the knowledge has been summarized and analyzed as the references for the investigations on the pro-posed new system, which includes low embankment structure, the response of the em-bankment under the traffic load, as well as the application and its reinforcement me-chanism of geocell structural layer.(2) The research of the applicability of the geocell structural layer as the lower layer is conducted dividing into two parts:the flexural capacity of the geocell structure layer and its anti-erosion ability. On the basis of the finite element analysis of the flexural capacity of geocell structure layer, a flexural modulus and mid-span deflection relations is established quantitatively. This can be used as a reference for the same type of experiment data processing. Subsequently,6trials based on superposed beam theory are designed to study the of geocell structure layer bending modulus determination and its influencing factors. The trial results show that the expanded width of the geocell has great influence on the bending modulus, geocell should be expanded as far as possible to nearly diamond shape. Analysis of the rigid pavement base erosion me-chanism indicates that, the internal reason of flushing phenomenon can be attributed to the soak softening effect of the free water accumulated in the bottom of the board, the external one due to repeated flushing of the hydrodynamic pressure caused by traffic. The utilization of the geocell gravel structure layer can not only form a good drainage channel under the rigid pavement to make the infiltrated water drain in time, but also be softened slightly by the water because of its unique strength and stiffness formation mechanism. Learning from the successful experience of the geomembrane bag against erosion, a layer of permeable geotextile is adopted to put on the geocell structure layer, to reduce the direct scouring action of the hydrodynamic pressure, thus to ensure its anti-erosion ability.(3) A comprehensive introduction on the main parts and their function of the GRLERPS in soft soil area is presented in this thesis, and its load bearing characteris-tics are further analyzed. Subsequently, the ADNIA is used to establish its plane strain model to calculate the proliferation problem of the stress and deformation in the em-bankment caused by traffic load. This model proves that the presence of the geocell structure layer will improve the stress state of the concrete pavement significantly and make the stress inside the roadbed decayed faster. In the engineering design of prac-tical calculation, the results reveal that the elastic foundation layer board model available in the existing norms can be utilized to analyze the load stress at the critical load position for the road panel of the new system.(4) By the finite element simulations, the deformation characteristics of the structure layer of the road with geocell are compared qualitatively with that without geocell. Results indicate that the geocell structure layer can effectively reduce the dif-ferential settlement of the foundation surface. Furthermore, it is found that the total settlement value reduced significantly by adopting geocell structure layer, in case of a comparative study of setting the same thickness of the same parameters geocell cu-shion on the ground surface. However, the performance of controlling differential set-tlement between the two methods is nearly the same. What is more, the orthogonal tests of three levels and seven factors that might affect the differential settlement be-tween the boards are designed. Variance and range analysis show various influence factors in this order from high to low:geocell structure layer thickness, the height of low embankment, the modulus of the soft soil, the modulus of low embankment, the modulus of the geocell layer, the thickness of road panel, the modulus of road panel. Thus, the most effective way, to control the differential settlement between plates, is to increase the height of geocell structure layer and the fill height of the low embank-ment.(5) Based on the similarity theory, two sets of the comparable model tests are de-signed and completed. To study the load bearing and deformation characteristics of the GRLERPS, six small items in the model test are divided into three stages to compare the difference of the performance between the two systems possessing the geocell structure layer or not. The simulation of periodic traffic load is carried out by a model car running back and forth on the roadway slabs. The car is drived by a novel link mechanical system which transforms the circular motions of concrete mixer into reci-procating linear motions. The model test results show that the proposed GRLERPS is feasible.更多还原