【作者】 魏丽敏；

【导师】 王永和；

【作者基本信息】 中南大学 ， 道路与铁道工程， 2005， 博士

【摘要】 稳定和过量沉降是软土地基工程中必须面对的两大问题。路基的过量沉降或不均匀沉降将导致线路运营条件恶化、乘客舒适度降低、甚至危及行车安全。严格控制工后沉降量是设计和修筑软土路基的技术关键,而合理、准确地预测沉降发展过程,又是经济合理地选择地基处理措施、科学安排施工进度、合理确定路面铺筑时间、有效减少工后沉降的技术基础。本文结合湖南省和广东省的相关科研项目,针对软土路基沉降分析和预测这一课题,基于粘弹塑性大位移问题的双重非线性流—固耦合分析方法,从室内试验、现场监测、理论研究、数值模拟到工程应用,进行了系统深入的探讨。主要工作有: 1.通过室内试验,分析了广东省西部沿海地区软粘土的基本物理力学特性、水理特性、应力—应变特性、应力历史特性等;并通过长期蠕变试验,研究软粘土的流变特性、流变参数、超载预压对软粘土变形规律的影响。 2.基于丰富翔实的现场实测数据,全面地分析了软粘土地基的竖向位移（沉降和分层沉降）、水平位移的发展规律和孔隙水压力的消散规律;获得了“薄层轮加法”施工对软土路基稳定性和变形的影响规律。研究表明,对具有明显流变特征的软粘土地基上分级修筑的路基进行双重非线性流—固耦合分析能更合理地考虑时间、荷载效应对变形的影响。 3.将任意固结度υ_i下土体强度指标φ_i、c_i与常规固结不排水剪试验所得强度指标φ_cu、C_cu或φ′、c′之间的关系引入Mohr—Coulomb屈服准则,提出了修正Mohr—Coulomb准则。首次提出了有限元分析中考虑软土地基强度随固结度增长的方法,该方法能合理地考虑强度增长对土体应力场、位移场的影响。 4.考虑软土变形的大位移、大应变、流—固耦合及依时性特点,创建了采用粘弹塑（西原）模型模拟土骨架,并采用动态“生”、“死”单元模拟路堤的施工过程,以及考虑强度随固结度增长的软土路基双重非线性流—固耦合分析模型,推导了用于增量分析的连续性方程和U.L.J.格式平衡方程,建立了分析软土路基的双重非线性有限元列式和迭代求解算法,并编制了大型实用化有限元分析程序LSVEP,该程序除了具有上述流—固耦合双重非线性分析与施工过程仿真分析更多还原

【Abstract】 Stability and excessive settlement are two important issues encountered in soft ground engineering. Excessive settlement or differential settlement of embankment will deteriorate the road condition., reduce the coziness of the passengers, and even threaten traffic safety. Therefore, strict control of settlement after construction is the technical key in design and construction of soft soil subgrade. Reasonable and accurate prediction of the development in settlement forms the foundation of economically and effectively choosing managing measures and scientifically planning construction schedule. What’s more, reasonable arrangement of paving time and effective decrease in settlement after construction are based on such a prediction.Aimed at settlement analysis and prediction of soft soil subgrade, this paper, on the basis of relative projects in Hunan province and Guangdong province and the Double Non-linear (visco-elastic-plastic and large strain) Fluid-solid Coupled Analysis Method, conducted a comprehensive and in-depth study, which included lab tests, field monitoring, theory analysis, numerical simulation and technical application. The issues conducted in this paper are generalized as follows:1. A series of lab tests were performed for the soft clay samples from the west coastal region in Guangdong province, to study the basic physical and mechanical property, permeability characteristic, tress-strain behavior and stress history. In addition, by means of long-term creep tests, rheological properties and parameters of soft clay were determined, and the effect of surcharge precompression on the deformation law of soft clay was obtained.2. Based on sufficient and creditable data from field monitoring, the developing tendency of vertical displacement (surface settlement and deep settlement), horizontal displacement and pore water pressure were analyzed comprehensively, and the effect of construction with ’Applied Folium Step by Step’ method on stability and deformation ofembankment on soft soil ground was acquired as well. The results show that the Double Non-linear Fluid-solid Coupled Analysis Method applying to staged filled embankment on soft clay ground with typical rheological characteristic may bring about more reasonable consideration of the effect from time and load on deformation3. The relationship between strength indexes (<pt and c.) under any degree of consolidation Ut and the strength indexes cra and ^ (or c and <p ) from routine CU-test was introduced into Mohr—Coulomb yield criterion and used to modify it. It was proposed for the first time that the fact that the strength of soft soil ground increases with the increase in the degree of consolidation should be taken into account while employing finite element analysis. This proposal calculates rationally the effect of strength increase on stress field and displacement field of soft ground.4. Based on the deformation characteristics of large displacement, large strain, fluid-solid coupling and time-dependence of soft soil, the analysis model was built independently, in which the soil skeleton was simulated by Visco-elastic-plastic Model, the embankment construction process was simulated by dynamic "Birth" and "Dead" elements and the Double Non-linear Fluid-solid Coupled Analysis Method concerning the fact that the strength increases with the increase in the degree of consolidation was established. The continuity equation and equilibrium equation of U.L.J. form for increment analysis were derived and the finite element formulas and iterative solution for double non-linear problems of soft soil subgrade were established. Additionally, this paper developed a large-scale practical finite element analysis program LSVEP, which provided not only emulational analysis for construction process and Fluid-solid Coupled Non-linear Analysis, but also various methods for various sites, calculating the degree of consolidation, which varies with time in construction5. Sensitivity analysis of 9 parameters was conducted deeply to investigate the effect of parameter change on developing trend of ground surface settlement, deep settlement, horizontal displacement and pore water pressure. Finally, it proved that the sensitivity of influence from each parameter on ground settlement was as follows order: Poisson’sratio jo., coefficient of permeability k, angle of internal friction tp, elastic modulus Ee, flow coefficient of viscoplasticity yvp, cohesion c, the ratio of &i/￡2,viscoelasticity modulus ijve,flow coefficient of viscoelasticity yve.6. On the basis of double non-linear fluid-solid coupled mechanical model proposed in this paper, the optimum mathematic model for parameters was obtained, which took advantage of the Flexible Tolerance Method appropriate to various observation information. Furthermore, back analysis method of calculation parameter of embankment was formed and relevant calculating program BAVEP was developed. Resorting to the Monte-Carlo Method, this paper first acquired general optimum solution, settling the puzzle that the use of Flexible Tolerance Method is liable to result in partial optimum solution. For the application to projects, "the Stages Multi-level Dynamic Construction Parameters Back Analysis Technology" was established acceptable for parameter back analysis of soft soil subgrade. As was indicated in practical projects, this technology was available and effective. The acquired parameters can synthetically reflect effects imposed by geologic condition, soil distribution, drainage property and loading course, and so on. The theoretical values were coincident well with the measured values, which validates the theory in this paper is correct and the program is credible.7. An organic system for settlement prediction of soft soil subgrade, Parameter Back Analysis Settlement Prediction Method, was established, in which the counting parameters were determined by back analysis program BAVEP, and the settlement prediction was performed by means of the double non-linear fluid-solid coupled analysis program LSVEP. Compared with Fitting Curve Method and Unequal Time-interval Model of Recent Information of Identical Dimension GM(1,1) Grey Model, the Parameter Back Analysis Settlement Prediction Method obtained in this paper bears the characteristics of clear physical meaning and constitutive relation, and of reasonable parameter selection. The settlement law reveals the settlement essential of soft soil subgrade, especially the fact that the settlement during late period is in good coincidence with the measured settlement, so it is of important significance in theory and practical value to predict the settlement after construction and determinethe time of construction of pavement.更多还原