武广客运专线红粘土地基沉降数值分析及试验研究

【作者】 李珍玉；

【导师】 王永和；

【作者基本信息】 中南大学 ， 岩土工程， 2009， 博士

【摘要】 红粘土是一种区域性较强的特殊土类,普遍认为它是一种较好的天然地基和良好的建筑材料,同时却因为具有明显的收缩性、裂隙性和分布不均匀等工程特性而存在着工程隐患。随着我国西部大开发战略的实施,在西南、华中、华南等红粘土地区修建高速铁路所遇到的红粘土问题也越来越多。对红粘土已有的研究成果尚很难解决高速铁路无砟轨道对地基沉降量严格要求的问题。因此,进一步深入地开展红粘土工程特性的研究具有重要的理论和工程实际意义。为此,结合武广客运专线建设的实际需要和铁道部重大研究课题,综合分析了国内外在该领域的研究现状,并应用室内土工试验、原位测试、现场工程监测及理论分析和数值模拟相结合的方法,对超固结残积层红粘土这一特殊土的变形规律,获得的主要结论和研究成果如下:(1)基于武广铁路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,获得该区域典型红粘土的工程特性参数。采用概率统计的方法分析红粘土各土性参数的空间变异规律,建立了各指标间的经验关系。研究了红粘土随埋置深度的增加,其含水量、孔隙比、液限、塑限、液性指数、塑性指数、压缩模量、前期固结压力等指标的变化规律。(2)通过室内大量固结压缩试验和三轴剪切试验,系统地研究了红粘土的应力历史、不同应力水平下的应力应变特性、不同固结状态下强度参数的变化规律,以及土层深度、围压等因素对红粘土强度和变形的影响情况。(3)在红粘土地基上进行了载荷试验及静力触探试验,分析了典型工点所得红粘土地基的沉降变形曲线,及其在外荷载作用下的变形规律。将不同深度的静力触探参数与室内土工试验进行对比,得到了两者参数之间的相互关系,并利用静力触探参数对红粘土地基土层的固结性状进行判断。(4)鉴于该区域红粘土的超固结特性,在分析红粘土地基固结沉降变形时,充分地考虑了其应力历史的影响。分析了在外荷载作用下,超固结红粘土地基可能出现的几种固结性状。对固结状态变化时的分界面采用临界孔隙水压力表示,并运用孔隙水压力消散水平表示其消散的程度。(5)考虑超固结比沿深度变化的特征,建立了超固结饱和红粘土的非线性固结控制方程。用有限差分法对固结方程进行数值计算,并用FORTRAN语言编制了相应的计算程序,获得了红粘土固结方程的有限差分数值解。用本文的方法结合课题的试验成果,分析了该区域红粘土在外荷载作用下的固结性状及其影响因素。(6)在工程应用中,对武广客运专线综合试验段的路基进行了373天的现场监测。根据现场监测的结果,分析路基填筑期间和完成后,红粘土地基的地表沉降、分层沉降及孔隙水压力的发展变化规律。除了运用本文方法对路基进行分析外,还采用有限元软件ADINA对红粘土路基进行数值模拟。将理论计算结果与监测值相对比,表明得到的理论分析值与现场测试结果之间较为吻合。(7)利用Bayesian理论对沉降修正系数进行了公式的推导。应用均匀分布的经验分布作为先验分布,在现场原位测试数据有限的条件下,利用小样本贝叶斯分析,建立了后验分布的概率密度函数,并采用马尔科夫链蒙特卡罗(MCMC)方法和Gibbs抽样法对该后验概率密度进行取样模拟,最大限度地利用有限的样本信息,推求出沉降修正系数的后验分布,进而对传统的沉降修正系数取值进行了优化。该方法最大程度地利用了以往的经验信息,充分地反映了其客观性。这一方法与岩土相关参数统计的实际过程一致,具有较高的应用价值,同时也为类似工程地基的沉降计算提供了又一条分析途径。更多还原

【Abstract】 Red clay is a stronger regional special soil type. It is considered that red caly is a good natural foundation and good building materials. At the same time, there are a lot of engineering problems because it has obvious shrinkage, cracks and uneven distribution, etc. With China’s western development strategy implementation, there would be inevitably more and more questions about red clay when a lot of high-speed railways will be built on red clay ground in the southwest, central and southern China areas. State-of-the-art research of red clay is still difficult to meet the strict requirements of the high-speed railway ballastless track. So the further research about engineering properties of red clay is of important theoretical and engineering practical significance. In this thesis, we carried out research combined the practical needs of the building of Wuhan-Guangzhou Passenger Line with the major research topic of the Ministry of Railways. Based on the comprehensive analysis of the domestic and international research in this field, combining soil experiments, in-situ testing, field engineering monitoring with theoretical analysis and numerical simulation methods, it has been discussed that deformation law of red clay with over-consolidation characteristics and some the practical problems in engineering application. Some conclusions and research achievement are obtained as follows.(1) Based on the engineering geological investigation report of Wuhan-Guangzhou Passenger Dedicated Line and the results of many soil tests, the engineering properties parameters of typical red clay were obtained. Using the method of probability and statistics, this thesis has discussed the spatial variability of soil parameters. Many experiment relationships among these indicators have been set up. It was found that the change law of many indexes increased with depth increasing at red clay natural profile, such as water content, void ratio, liquid limit, plastic limit, liquid index, plasticity index, compression modulus, pre-consolidation pressure, etc.(2) Through a large number of compression tests and triaxial shear tests, it has been studied systematically that the stress-strain characteristics at different stress levels and the change regularity of intensity changes of the parameters under the different consolidation states. Also, it has discussed some factors influencing the red clay strength and deformation is discussed, such as soil depth, confining pressure and others.(3) Through the plate load tests and cone penetration tests on the red clay ground in typical region, the settlement deformation curves and deformation rules of red clay ground under load are obtained. Compared the parameters of different depths soil gotten by cone penetration test with those gotten by soil experiments in room, some relationships between parameters have been obtain. According to the results described above, consolidation behavior of red clay foundation can be judged.(4) In view of the over-consolidation characteristics of red clay, the influence of stress history on consolidation settlement of red clay ground has been taken into account fully. Several consolidation behaviors may occur when over-consolidation red clay foundation is under load. The critical pore water pressure is used at the time of consolidation of state changes. The level of pore water pressure dissipation is used to represent the extent of its dissipation.(5) Considering the changes of over-consolidation ratio with the soil depth increasing, it is built to analyse the nonlinear consolidation equations of over-consolidation saturated red clay. The numerical solution of consolidation equation has been obtained by means of Finite difference method and FORTRAN program. Combined the method suggested by this paper and test results, it has been analyzed that consolidation characteristics of red clay and its influences under load.(6) In engineering applications, there is 373 days in-site monitoring the roadbed of the Wuhan-Guangzhou Passenger Dedicated Line integrated test section. According to the results of site monitoring, it is discussed that development and change regularity of red clay ground surface subsidence, layered settlement and pore water pressure. In addition to the method suggested, Finite Element Method is also taken to numerical simulate using software ADINA. Theoretical calculation results are compared with the site monitoring value, which shows that theoretical value are more in line with the field test results. (7) This thesis derives the formula of settlement modified coefficient using Bayesian theory. Uniform distribution of the experience distribution is used as prior distribution. Under conditions that in situ test the datum are very limited, the posterior distributions of the probability density function are set up using Bayesian analysis of small samples. And posteriori probability densities of the samples are analog by means of Markov Chain Monte Carlo (MCMC) method and Gibbs sampling method, which makes fully use of limited sample information to infer posteriori distribution of settlement modified coefficient. The tradition settlement modified coefficient has been optimized through this method. In this way, the past experience has been used farthest extends, which fully reflects its objectivity. This approach coincides with the actual statistics process of the geotechnical parameters and has a high application value. In addition, it can provide alternative way to carry out settlement calculation for similar projects.更多还原