【作者】 吴丽君；

【导师】 蒋关鲁；

【作者基本信息】 西南交通大学 ， 道路与铁道工程， 2011， 博士

【摘要】 饱和土理论作为土力学的基石,理论体系已经日趋成熟,并且在工程实际中得到广泛应用。与饱和土相比,非饱和土在自然界中的分布范围更广,在工程实际中的应用也更多,其工程特性更为复杂,但理论体系尚不十分完善,工程应用有很大的局限性。尤其是受到试验条件的限制,我国对非饱和土的研究还处于起步阶段。非饱和土研究包括固结理论和强度理论两个重要组成部分。在岩土工程中,这两个部分分别对应岩土体的变形和稳定。现代高速铁路的设计和施工,以沉降变形控制为先导,同时满足系统的强度和稳定性要求。为保证线路的安全性和平顺度,既有规范已经对高速铁路工后沉降作出了明确而严格的规定。因此,对于不同种类的非饱和土,根据自身特点建立合理的固结理论和适用可靠的计算方法显得非常重要。从非饱和土的分类出发,考虑非饱和土四相组成及各项组分的特点及其与饱和土的差异,在非饱和土中除作用在土骨架上的净应力以外,还有作用在收缩膜上的孔隙气和孔隙水所形成的基质吸力。饱和度的高低决定了土中孔隙水和孔隙气的分布形态及流体的运动规律,进而影响到基质吸力的大小。宏观上,非饱和土的饱和度(基质吸力)直接或间接决定了其固结压缩特性和渗透性,易造成地基沉降不均匀、工后沉降过大、工期规划不合理及地基处理成本增加等弊端。本文基于既有的非饱和土理论,针对胶济客运专线沿线广泛分布的深厚非饱和土(粉质粘土和粉上)开展大量的试验和计算,阐明了与水土特性相关联的非饱和土固结压缩特性,在此基础上结合饱和土理论研究非饱和土渗透系数和相关固结参数。笔者通过对比离心机模型试验和长期沉降观测成果,分析深厚非饱和土地基沉降变形特性和应力传递机理,进而提出适用于非饱和土(粉质粘土和粉土)的沉降计算理论。本文的研究工作主要包括以下几个方面的内容：(1)概括已有的非饱和土研究成果,提出适用于高速铁路深厚非饱和土地基沉降计算和分析的新思路和新方法。(2)通过固结试验和控制基质吸力的固结试验,对华北和胶州地区的非饱和粉土、粉质粘土进行重新分类,重点对非饱和土的水土特征和变形特性进行研究。对比饱和土的相关特性,结合水土特征曲线和体积变化规律预测非饱和土的渗透系数和固结系数等影响地基沉降与时间关系的重要参数变化。考虑到空气的扩散性和不易量测的缺点,本文提出简化的非饱和土固结方程,对非饱和土地基沉降曲线进行修正使其与工程实际更加吻合。在此基础上,利用有限元程序分析不同工法下的非饱和土地基沉降变形和应力分布,以优化高速铁路非饱和土路基填筑工艺和工期规划。(3)离心机模型试验采用分层填筑和一次性填筑两种方式对未加固地基、强夯加固地基和水泥搅拌桩加固地基四组模型的沉降变形规律和荷载传递机理进行研究。研究结果表明,以上四组模型填筑期和放置期内地基完成沉降量占总沉降的70%以上,路基填筑完成之后放置1.5年,地基沉降完全稳定。分层填筑的地基沉降明显小于一次性填筑的地基沉降,控制路基填筑速率,优化路基填筑工艺可降低高速铁路路基地基沉降变形。离心机模型试验分别测试路基基底中心和路肩处基底应力,双层地基的基底应力分布和附加应力衰减与未加固地基类似。实测基底中心应力介于比例荷载和均布荷载之间,基底应力分布和附加应力衰减与路基宽高比有关。结合弹性路堤法、离心机模型试验和Plaxis有限元计算结果,本文提出改进的附加应力和基底应力计算方法。运用改进方法计算地基沉降可解决布氏理论计算值远远大于实测值的问题,从而缩短工期,降低地基处理成本。(4)根据胶济客运专线的地基土性质和工程实际需要,采用平板荷载试验、旁压试验、静力触探试验和标准贯入试验量测非饱和土地基各项岩土参数。结合现场长期沉降观测成果,对比现场原位测试与室内试验所获得的岩土参数,分析各种原位测试方法的适用范围和适用条件。为了尽可能减小试验过程中地基变形所引起的土层结构性变化和吸力波动,笔者提出适用于胶济线非饱和粉土、粉质粘土地基的原位测试方法及合理的岩土设计参数。试验结果表明,胶济客运专线浅层松软土地基的静力触探试验结果与实测沉降值吻合。由于标准贯入试验成本低廉,操作方便,试验数据相关性较好,能全面、真实的反映非饱和土地基岩土性状。本文通过分析典型工点的标准贯入试验数据,提出胶东半岛及华北部分区域非饱和粉土、粉质粘土的压缩模量与标贯捶击数的经验修正公式,不仅为标准贯入试验在非饱和土地基原位测试中的应用提供了广阔的前景,也为进一步完善高速铁路非饱和土地基原位测试技术提供了科学依据和理论基础。(5)现场长期观测通过监测非饱和土地基竖向沉降、水平位移、深层沉降以及孔隙水压力变化分析其沉降变形特性,确定地基压缩层厚度,检验地基加固效果,验证非饱和土地基沉降计算理论和工后沉降预测方法的正确性。观测结果表明,填筑期内地基沉降可完成总沉降的80%-95.8%。天然地基距地表以下6m范围内沉降量大,约占总沉降的55%以上。非饱和土地基经换填、强夯和水泥搅拌桩处理后,地基沉降量和侧向位移明显减小,系统整体约束性和抗变形能力增加,路基沉降均匀,稳定性良好。与传统的布氏理论相比,天然地基和双层地基采用改进后的基底应力和附加应力计算地基沉降,与现场实测值更加接近。(6)综合以上试验及计算分析成果,对换填、强夯和水泥搅拌桩加固后的地基加固效果进行检验。现场观测和有限元程序计算表明,换填和强夯加固非饱和粉上、粉质粘土地基的承载力提高,压缩模量增大,地基沉降减小,但沉降稳定时间有所增加,工后沉降量反而增大。相反,水泥搅拌桩加固非饱和土地基,沉降速度快,工后沉降小,有利于非饱和土地基沉降变形控制,适合非饱和土地基加固。更多还原

【Abstract】 Soil mechanics based on saturated theory, which has already been gradually maturing and widely applied to engineering practice. Compared with saturated soil, distributing scope of unsaturated soil is wider in nature. Unsaturated soils have been also applied on engineering practice more widely, which engineering menchanic characteristics are more complicated. However, the theory system of unsaturated soil is still not quite perfect. Engineering applications are also limited. Specailly, because of experimental condition’s restriction, researches on unsaturated soils are in the beginning stages in our country. The researches on unsaturated soil mainly included consolidation theory and strength theory. In geotechnical engineering, these two parts controlled distortion and stability for rock and soil mass. Design and construction on high speed railway declined to control settlement and distortion, and satisfied strength and stability requests of system. In order to ensure the safety and smooth degree, the current norms have made explicit and strict rules for post construction settlement of high speed railway. Therefore, according to self-characters, it’s very important to establish rational consolidation theories and applicable computation methods.Considering the fact that four phases composite and individual characteristics of different component as well as their differences of saturated soils, the difference between pore-air pressure and pore-water pressure on water-air interface constituted matric suction in addition to the net stress which is imposed on soil skeleton. The saturation degree decided the distribution form and movement rule of pore-air and pore-water in soil, and then influenced the matric suction. On the macro view, the saturation degree directly or indirectly decided consolidation and compress characteristics and permeability. According to existing saturated theory, this text illustrated the consolidation and compression of unsaturated soil in relation to water-soil characteristic through many experiments and computation for deep unsaturated soil (silty clay and silt), which widely distributed along JiaoZhou-JiNan passenger dedicated railway.We researched the permeability coefficient and consolidation parameters of unsaturated soil. Comparing the centrifugal model experiment and long-term settlement observation results, author analyzed the foundation settlement characteristic and stress transfer mechanism, and put forward settlement computation theory applicable to unsaturated soils (silty clay and silt).The textual research work mainly included several contents as follow:(1)Generalizing previous research results of unsaturated soil, author put forward new thoughts and new methods adapting to settlememnt computation and analysis of unsaturated soil foundation for high-speed railway.(2)Reclassified the unsaturated silt and the silty clay through consolidation test and consolidation test under controlling matric suction.We specially researched water-soil characteristics and deformation characters toward unsaturated soils. Comparing the characters of saturated soil, predicted many important parameters, which permeability coefficient and consolidation coefficient influenced the relation between foundation settlement and time. Considering the air diffusion and the weakness of not easy measure, this text brought forward simplified consolidation equation for unsaturated soils, then revised the curves of foundation settlement to come close to engineering practice. On this condition, took advantage of finite element program to analyze the settlement deformation and stress distribution of unsaturated soil under different technique. At the same time, we optimized the subgrade filling technologies and construction time planning.(3)Centrifugal model experiment adopt filling in layers and one-off filling to research the settlement deformation regularity and loading transfer mechanism toward untreated foundation, dynamic compacting foundation and reinforced by cement mixing piles.Results showed, above four models’settlement have achieved more than 70% of total settlement in filling stage and placement stage, embankment settlement have been stable after placing 1.5 years.The embankment settlement by filling in layers is less than one-off filling, which settlement of embankment and foundation for high-speed railway could reduce settlement by controlling the speed of filling and optimizing the filling technology. Centrifugal model experiment respectively tested base center stress and stress under subgrade shoulder, the base stree distribution and additional stress attenuation for double-layer foundation are same with untreated foundation. The measured base center stress is intermediate between proportion load and uniform load, which are relevant to aspect ratio. Combining elastic embankment method, centrifugal model experiment into computation results by Plaxis Element Program, modified calculation methods for the base center stress and the addition stress. Using modified formula calculated foundation settlement solved the solution of Boussinesq was greater than the measured value. At the same time, we could shorten the construction time and reduced the cost of disposing foundation.(4)According to the properties and engineering practical requests of JiaoZhou-JiNan passenger dedicated railway, geotechnical parameters are measured by plate loading test, pressure-meter test, static cone penetration test, standard penetration test. Combining the long-time settlement observation results, author contrasted the geotechnical paramaters between the in-situ tests and laboratory tests, analyzd kinds of in-situ tests’adaptability. For reducing the structural movement and suction fluctuation on foundation in test processes, author presented appropriate in-situ tests and geotechnical parameters toward unasaturated silt or silty clay. Experiment results showed the results of static cone penetration test accorded with value of practice。Beacause standard penetration test has low cost and operational, experiment data have perfect correlation, comprehensively and truly reflected the geotechnical characters of unsaturated soil. In this text, analyzed the datum of standard penetration in typical construction poins, and bought forward the modified fomula for unsaturated silt and silty clay in JiaoDong peninsula and north china section. Above conclusions not only provided wide foreground for the application of standard penetration test on the in-situ test technology for unsaturated soil, but also perfected in-situ tests for the unsaturated soil foundation of high-speed railway.(5)The field long-term observation analyzed the characteristics of settlement and distortion though monitoring vertical settlement, horizontal displacement, deep settlement and pore water pressure.Then author ensured the thickness of compressive layer and inspected the reinforcement effect. At last, validate the settlement computation theories and post construction settlement prediction methods. The observation results showed, the seetlement account for 80%～95.8% of total settlement. The settlement and lateral displacement of unsaturated soil evidently reduced after reinforced by replacement, dynamic compacting and cement mixing piles. Integrity restriction and anti-deformation capability has been enhanced. The subgrade settlement is uniform. And the embankment has favorable stability. Comparing to traditional Boussinesq theory, the settlement of natural foundation and double-layered foundation are close to practice value with modified base center stress and additional stress.(6)Synthesising above test fruit and calculation analysis, inspected the foundation reinforcement effect for replacement, dynamic compacting and cement mixing piles. Field observation and element program computation showed, if the unsaturated foundation is reinforced by replacement and dynamic compacting, the bearing capacity and compression modulus has been enhanced. Therefore, the settlement decreased, but post settlement increased.On the opposite, if the unsaturated foundation reinforced by cement mixing piles, the speed of settlement is slow, and the post settlement is small. So it’s bennificial to controll the unsaturated foundation settlement更多还原