客运专线红黏土地基固结变形及桩网加固机理现场试验

【作者】 王亮亮；

【导师】 杨果林；

【作者基本信息】 中南大学 ， 岩土工程， 2010， 硕士

【摘要】 红黏土是一种区域性较强的特殊土,在天然红黏土地基的竖直剖面上,红黏土的稠度状态自地表往下依次为坚硬-硬塑→可塑→软-流塑。一般情况下,处于坚硬、硬塑和可塑状态的红黏土层层厚远远大于软-流塑状态的土层厚度,对于普通建筑,红黏土可作为天然地基或建筑材料,但由于红黏土具有明显的胀缩性、各物理力学指标试验数据离散性大、裂隙性、分布不均匀等工程特性而会给工程建设带来安全隐患。随着我国高速铁路网规划的出台,高速铁路建设的全面铺开,在高速铁路修建过程中遇到的红黏土问题也越来越多。红黏土广泛分布于我国的西南、华中、华南地区,现阶段我国高速铁路规划网中有多条线路经过该地区,而目前对红黏土的研究成果尚很难满足高速铁路无碴轨道对地基沉降量严格控制的要求。为确保工程质量,高铁红黏土地基大部分采用桩(CFG)网复合地基的方法加以处理。国内外关于桩网复合地基的研究比较多,但岩土工程中土体种类、状态等的变化,会引起土体工程性状发生相应的变化,进而对地基的加固效果产生影响,现阶段,针对桩网复合地基加固处理红黏土地基的研究资料不多见。为此,结合武广客运专线建设中的实际需要、国家自然科学基金项目和铁道部重大研究课题,进一步深入地开展红黏土工程特性和红黏土桩网复合地基处理方面的研究工作,具有重要的理论和工程实际意义。主要内容归纳如下：(1)基于武广客运专线沿线工程地质勘察报告,通过大量的室内土工试验,获得该线典型红黏土的工程特性参数。采用概率统计的方法分析红黏土各物理力学指标,获得了各指标的均值,置信区间,建立了各指标间的经验关系；聚类分析表明红黏土的常规物理力学指标基本上可分为结构、强度和状态三类；主成分分析表明可利用综合主成分值进行红黏土路用性能的评价。(2)选取线路一红黏土横断面,在不同深度埋设单点沉降计,孔隙水压力计,监视红黏土地基不同深度的沉降和孔隙水压的变化,并在监测断面附近不同深度钻孔取样,进行室内固结及膨胀性实验,根据现场监测数据和室内试验结果,研究了红黏土地基的变形特性及其内在机理。(3)在CFG桩加固段一横断面,在褥垫层中桩顶和桩间土位置格栅上间隔安装柔性位移计,测试加筋体土工格栅随荷载、时间的变化情况,结合实验结果深入分析格栅变形规律。(4)预先在CFG桩内埋设混凝土应变计进行实时监测,结合室内常规土工试验,研究了红黏土地基中CFG桩桩身不同位置应变随荷载、时间的变化规律及其内在作用机理。(5)在调研国内外现有的桩承式路堤土拱效应计算模型基础上,分析了各模型的局限性,针对大部分路基,其填筑高度较小,路基填料为散体材料等特点,对桩承式路堤拱效应计算模型进行了新的探索。更多还原

【Abstract】 Red clay is a kind of special soil with strongly regional characteristic. On the vertical section of natural red clay foundation, consistency state of red clay could be divided into three types:hard plastic state→plastic state→soft flow～mould state. Generally, the layers with hard plastic state or plastic state are thicker than the soft flow-mould state layers. For normal constructions, it is considered that red clay is a good natural foundation and good building material. However, there are a lot of engineering problems because of it’s obvious dilatability and contractibility, large discreteness of its physical and mechanic parameters and uneven distribution, etc. With high-speed railway network plan has been carried out, the work of high-speed railway construction is now in full swing, and red clay engineering problems in construction are increasing.Red clay is widely distributed in southwest, southern, central china areas. Research productions of red clay which have been obtained are difficult to meet the strict requirements of ballastless track of high-speed railway. To guarantee the quality, designers use pile-net composite foundation to reinforce red clay foundation. Researchers at home and abroad have done lots of works about pile-net composite foundation. Different soil has different engineering characteristics, so the work-mechanism of pile-net composite foundation will change with soil type. On the stage, there is rarely data about red clay pile-net composite.So the further research about engineering properties of red clay is of important theoretical and practical significance. In this thesis, combined with the practical needs of Wuhan-Guangzhou passenger dedicated railway, we have carried out researches with the supports of national natural science foundation of china and Ministry of Railways. The main achievements are as follows:(1)Based on the engineering geological investigation report of Wuhan-Guangzhou passenger dedicated railway and the results of many soil tests, the engineering properties parameters of typical red clay have been obtained. using the Theory of Multivariate Statistical Analysis, through statistic analysis, mean and 95% Confidence Interval for mean of each parameter are obtained. What more, many experimental relationships among these parameters have been set up. Hierarchical cluster analysis indicates the property of red clay can be divided into three parts:structural index, strength index and status index. Principal component analysis indicates that values of comprehensive principal component can be used to assess road performance of red clay.(2) Embed single-point settlement sensors and pressure gauges at different depth of red clay foundation to measure deformation and pore pressure. Combined with results of consolidation and swell-shrinking test, system analysis of red clay foundation deformation character and its mechanism have been done.(3) In a cross section of red clay foundation where reinforced by CFG piles, flexible displacement meters have been fixed on the geogrid of pile top and between piles location to monitor the geogrid deformation as load and time change. Combined with monitoring results, the deformation mechanism has been analysis deeply.(4) The concrete strain meters have been buried in CFG piles to monitor the deformation. Combined with the results of laboratory tests, the behaviors of CFG pile which were changed with load and time and the internal interaction mechanics between pile and red clay are studied.(5) Through investigating computational model of soil arching effect of subgrade with Composite Foundation, limitions of these models have been analyzed. Considering that fill heights of most subgrads are not tall, and their fill materials are granular materials, a new computational model of soil arching effect has been established in this thesis. But there are a lot of works need to do to improve the model.更多还原