【作者】 李朝晖；

【导师】 张虎元；

【作者基本信息】 兰州大学 ， 地质工程， 2011， 博士

【摘要】 近年来中国汽车工业飞速发展,自2009年中国已经成为汽车产销第一大国。随着相关环境保护及汽车轮胎报废法律的日趋健全,废轮胎问题逐渐凸显。废轮胎问题是指：废轮胎作为固体废弃物,因其体积庞大不易直接填埋；直接焚烧会严重污染空气；传统处理方法如裂解、派生燃料、生产低等级橡胶制品等不能完全处置数量逐年上升的废轮胎。废轮胎处理已成为世界范围的环境问题。许多发达国家针对废轮胎问题除了采用传统的处理方法外,已将完整废轮胎、轮胎破碎物或称轮胎派生骨料(Tire Derived Aggregates,TDA)与天然土的混合物应用于岩土工程中。该领域近三十年的研究表明,废轮胎不易降解的“缺点”在岩土工程中可成为建筑材料耐久性的“优点”,同时因废轮胎具有轻质、隔热、高弹性、高摩擦性等特点,可用于天然土的改良,解决与应力、变形有关的岩土工程问题,如路堤回填、边坡支当、软弱地基处理等。我国黄土地区涵洞开裂问题十分普遍,素有十涵九裂之称。修复开裂涵洞难度大、费用高且影响道路畅通。因此涵洞开裂问题成为黄土地区岩土工程亟待解决的课题。本文借鉴发达国家的废轮胎处理经验,首次进行了废轮胎在我国岩土工程领域内的相关研究。从“以废治害”的思想出发,为废轮胎寻找在岩土工程中的新用途,同时开发出新型优质岩土工程材料,解决困扰公路建设的涵洞开裂岩土工程问题。研究对象为废轮胎颗粒与黄土混合物,以下简称GR-LM(Granulated rubber-Loess mixtures)。本文通过室内试验、现场试验、数值模拟等方法对GR-LM进行了岩土工程特性研究,测试了废轮胎颗粒及其与黄土混合物的基本物理、力学指标,研究了经典本构模型的适用性,通过现场试验验证了数值模拟方法的可行性并进一步验证了本构模型的适用性,采用数值模拟方法对涵洞减荷设计进行优化,为工程实践提供参考。本文的主要研究内容和取得的研究成果包括：1、物理特性研究测试了废轮胎颗粒的比重、吸水率,研究了废轮胎颗粒与黄土混合后密度的变化规律,发现随废轮胎颗粒体积掺量每增加10%密度减小0.78kN/m3。废轮胎颗粒的比重略高于水,吸水率很小,可以忽略。2、压实特性研究将废轮胎颗粒以0%-50%的掺量与黄土混合,研究了GR-LM的轻型、重型动力压实特性。试验研究发现,废轮胎颗粒掺量小于20%的混合土,其压实特性类似于黄土,掺量大于40%的混合土其压实干密度变化较小,且随废轮胎颗粒掺量的增加混合土最大干密度与最优含水率均减小。轻型击实能下30%掺量及重型击实能下40%掺量状态细颗粒充分填充孔隙,GR-LM压实效果显著。3、压缩特性研究RG-LM压缩特性介于纯压实黄土与纯废轮胎颗粒之间,总体随掺量增加压缩系数增大、压缩模量减小、可恢复应变增加。低应力条件时掺量约30%的GR-LM应变较小,随掺量增加GR-LM压缩模量减小。混合物内部颗粒接触结构类型及颗粒刚度特性是压缩特性变化的主要原因。4、应力-应变及剪切特性研究通过直剪试验和不固结不排水三轴试验对GR-LM的应力-应变及剪切强度特性进行了研究,试验结果发现除纯压实黄土外几乎所有混合物试样均表现出应变硬化特点。影响混合物剪切特性的因素主要有掺量、基质土密实程度、围压等。混合物剪切强度表现出随界限掺量呈区间性变化。在三轴试验应力范围内混合物没有出现明显的峰值强度,中、低压力下使剪切强度增大的最优掺量是30%和40%,直剪试验中,轻型击实能试样的最佳掺量为30%,重型击实能试样的最佳掺量为40%。掺量大于50%的混合物,体积应变表现出完全的收缩特性,应力-应变表现出近似线性。从细观结构角度对控制混合物抗剪强度的界限掺量进行了分析,利用孔隙充填模型和粘土基质物理状态的概念,合理阐释了废轮胎颗粒掺量对混合物抗剪强度的控制机理。5、GR-LM本构关系利用常规三轴压缩试验数据,得出了GR-LM双曲模型参数。采用该模型对不同围压下GR-LM的应力-应变进行预测并与试验数据进行对比,考察双曲模型的适用性。对比发现双曲模型只适用于低掺量(小于30%)GR-LM。30-40%掺量混合物表现出应力敏感性,低、中应力下其偏应力-应变基本符合双曲模型,高应力下表现为近似线性关系。高掺量(大于50%)GR-LM及纯废轮胎颗粒宜采用弹性模型。6、涵洞减荷效果检验及优化通过测试某高速公路方形盖板涵涵顶土压力,发现涵洞上方填筑一定掺比的TDA-LM后,涵顶土压力由高于涵侧14.8%变为低于涵侧20.6%。通过数值模拟试验对公路涵洞上方填筑GR-LM减荷设计进行优化,认为减荷效果可以通过调整减荷材料的掺比、铺筑位置、宽度、厚度达到最佳,铺筑减荷材料后可以改善涵顶、涵侧沉降及土压力分布曲线性质,对涵顶具有明显的减荷作用。通过上述研究得出GR-LM可用于岩土工程中,可改良黄土工程特性,是一种新型土工材料。将其用于岩土工程中可消耗大量废轮胎从而开辟新的废轮胎处理途径,同时另一方面节约天然土资源,并为解决与应力变形有关的岩土工程问题(如涵洞减荷)提供了新的方法。更多还原

【Abstract】 Automobile tires are becoming a large volume of solid waste that is prohibited to come into landfill site. China has been the first automobile producer and seller in the world since 2009. The problem of disposal scrap tires are seriously with the legislation of environment protecting and the legislation of discard as useless of automobile tires. Scrap tires problem is that scrap tires as the large volume solid waste regarding not easy land filled is a disposal problem worldwide. Some of the natural reused scrap tires such as tire-derived fuel for energy generation, remanufactured tires, high way crash barriers, low-grade rubber products et al. Although these recycling, reuse efforts consume 70% of scrap tires, there are still a large amount tires cannot be disposal correctly.Industrialized countries have been undertaking over thirty years in studying the possibilities of using tire shreds or tire-derived aggregates (TDA) as lightweight materials in civil engineering. Geotechnical research indicated that TDA possess some potential properties compared to natural soils, such as high durability, strength, thermal insulation capacity. This new kind of geomaterial is successfully used in highway embankments and backfills behind retaining structures over weak or compressible soils foundation.It is necessary to perform the research of using TDA or TDA-Soil mixtures (TDA-SM) in geotechnical application in our country. The thesis studies the geotechnical properties of scrap tires and loess mixtures in China firstly with referencing the achievement of scrap tires disposal in civil engineering in developed country. Using "waste" to solve rode structure problem while can exploit a new high-profile geotechnical material and a new way of scrap tires disposal.The physical and mechanical properties of TDA and TDA-SM are different from natural mineral soils, changing with the tire style, tire grain size, tire content, matrix property, compaction manner et al. This thesis focus on the mechanical property of granulated rubber and loess mixtures (GR-LM) through laboratory study including compaction test, compression test, direct shear test, and unconsolidated undrained triaxial test. The test data are analyzed based on the macroscopic mechanical phenomenon of binary packing mini-fabric, and the relationship between shear strength and mini-fabric was explained. The major results are as follows:1. Physical properties of GR-LMThe specific density and water absorption of granulated rubber were tested. The density of granulated rubber loess mixtures decreased with increasing rubber content, at a rate of approximately 0.78 kN/m3 per 10% rubber content by weight. The specific of granulated rubber is slightly higher than that of water, and the water absorption is neglect.2. Compactibility of GR-LMThe compactibility of GR-LM was studied by standard and modified Proctor tests. The result shows that with the range of 0% to 20% of granulated rubber content,GR-LM has a similar compactibility to that of loess, but the dry density and water content of mixtures have a less change when the granulated tires content is large than 40%. An effectiveness compaction were gained when the compaction performed of 30% granulated rubber under Proctor compaction energy, and compaction performed of 40% granulated rubber under modified Proctor compaction energy respectively.3. Compression properties of GR-LMCompression tests have been used to investigate the compressibility of granulated rubber and loess mixtures. The result indicated that the compression properties of mixtures are between the compacted loess and the compacted granulated rubber. The modulus of compressibility of the mixtures decreases with increasing granulated rubber content, while the coefficient compressibility elastic strain increases with increasing content. One of the main reasons in changing of compressibility of mixtures was interpartical contact structure. The elastic of granulated rubber causes an increase of low modulus of compressibility. It was considered that the property of modulus of mixtures varying with content could be used in geoengineering applications deal with deformation such as reducing load of culvert and dynamic stress release.4. Stress-strain and shear strength of GR-LMShear strength and stress-strain properties of GR-LM were investigated through direct shear test and unconsolidated undrained triaxial test. The effects on shear strength of varying confining pressure and rubber content w evaluated. It is found that GR-LM is stress-strain hardening behavior except for specimens of pure loess at low confining pressure. The test results showed no well-defined clear peak shear strength. The optimum granulated tire content (i.e., the one leading to the maximum shear strength) was about 30% at low and medium confined pressure (50-100kPa) in triaxial test. The optimum granulated tire content in direct shear tests was about 30% and 40% at Proctor compaction energy and modified Proctor energy respectively. Tests showed that the content of 30-40% was found to be sensitive to the shear strength of GR-LM under different confining pressure used in this study. The GR-LM with sensitive content shows high strength at low confined pressure (<100kPa) and hybolic, but shows nearly line deviatoric stress-strain behavior at high confining pressure (>200kPa). When the content of GR-LM are over 50% showed fully contractive volumetric strain behavior and nearly line deviatoric stress-strain behavior. The critical content of GR-LM is analyzed from the viewpoint of granulated rubber loess mixtures’s meso-structure. By combination of porosity structure and loess matrix state, the influence of rubber content on the shear strength of compacted GR-LM was reasonably explained.5. Constitutive model of granulated rubber and loess mixturesThe hyperbolic model is relatively simple, well validated and it reliably represents soil behavior. Parameters of hyperbolic for granulated rubber loess mixtures were calculated using data derived from conventional triaxial compression tests. The comparison between the hyperbolic model and the laboratory data is performed and the suitability of hyperbolic model can be used for low rubber content (less than 30%) mixtures. The mixtures with 30-40% rubber content shows sensitivity of stress-strain to stress. The deviatoric stress-strain of 30-40% mixtures under low to middle stress (<200kPa) can be described with hyperbolic model, while under high stress the deviatoric stress-strain expresses nearly line variation. Stress-strain behavior of high rubber content mixtures and of pure granulated rubber can be described with elastic model.6. GR-LM as load reduction materials and design optimizedThe earth pressure over square culvert were tested incite. The results shows that the earth pressure on the top of the culvert with filled GR-LM is less than 30% compared with earth pressure of no mixtures over culvert. Numerical modeling performs the load reduction design over culvert of filling mixtures. The effects of load reduction are connected with rubber content of mixtures, position of mixtures, width and thickNess of mixtures. It has been derived that use GR-LM lined on the culvert can change the behavior of soil pressure distribution and settlement on the top and side of culverts. The load reduction of culvert is distinct.It has been found that granulated rubber and loess mixtures are fit to use in geotechnical engineering applications. The salient benefits of using GR-LM can solve problems with stress and settlement in geotechnical engineering. The benefits include reducing density of fill, adequate stability (with the rubber content of about 30-40% at low or middle confined pressure), variable modular (with different content of rubber and different pressure, the modular of mixtures are different).更多还原