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基于变形场和应力场的土质边坡稳定性研究
中文摘要

鉴于目前边坡变形与稳定性研究中存在的问题:1)脱离地质基础、轻视前期现场勘察、忽视破坏模式的情况下来分析边坡稳定性;2)目前边坡稳定研究的热点—强度折减法,存在只对强度参数折减,没有同时考虑其他力学参数的影响及其相应的调整措施;3)现有边坡稳定性的评价方法不够完善,如常用的极限平衡法和强度折减法,没有将评价方法与现场实测的数据及数值计算方法得到的变形场和应力场联系起来;4)边坡稳定性研究中往往重评价方法的“精确计算”和计算方法的研究,而忽略研究岩土体参数对评价结果的重要性等。本文以土质边坡为研究对象,基于边坡的变形场和应力场,重点对边坡稳定性分析中存在的相关问题进行研究,包括:有限元强度折减法的改进;在数值计算分析中引入根据单元应力水平来调整变形模量的分析方法,并用改进方法研究边坡变形场和应力场的特点,探讨边坡稳定与变形之间的关系,研究确定边坡潜在滑动面的方法及如何确定边坡的变形预警值;滑带土强度特性研究及其参数的确定方法等。全文共分八章,每章的具体研究内容如下: 第一章全面回顾了边坡变形与稳定性的研究历史与现状,并综述了包括极限平衡法、极限分析法和有限元法在内的多种边坡稳定性分析方法,比较了各种方法的优缺点,分析了它们之间的联系与区别。在此基础上,总结了边坡变形与稳定性研究中存在的问题,确定了本文的研究内容。 第二章分析了拉格朗日方法(FLAC)的力学背景、基本特点及计算公式等,找出其在岩土工程应用中的优缺点,并通过对其进行二次开发来实现本文的部分研究内容。 第三章对有限元强度折减法分析边坡中的若干问题进行了深入分析和研究,主要包括:1)失稳判据;2)剪胀角变化对边坡安全系数和滑动面位置的影响;3)重点对目前的强度折减法进行改进,改进后的方法在计算时不仅对强度参数c和f折减,对变形模量E和泊松比v也进行调整。研究发现,将变形模量E和泊松比v根据单元应力水平进行调整后对边坡安全系数、主应力差、最大剪应变γ〓、变形场、应力场和塑性区等均有影响。具体规律是:与折减泊松比v相比,折减变形模量E对应力和应变的影响更大; E和v折减后得到的边坡安全系数F〓比E和v不折减时获得的要小;E和v折减后滑移带位置差异不大,但是滑移带的带宽差异比较明显;E折减后的塑性区范围扩大。本章强度折减法的改进是通过对拉格朗日差分法(FLAC2D)软件经过二次开发实现的。 第四章基于目前数值计算方法分析边坡时采用固定变形模量存在的不足,根据邓肯-张模型(Duncan and Chang,1970)原理以及在第三章研究成果的基础上,经过对邓肯-张模型的简化,建立了变形模量E随土体应力水平变化而变化的计算方法,并总结了在没有压板试验数据的情况下,几种确定初始变形模量E₀的方法。对比计算结果知,与传统采用固定变形模量的计算方法相比,改进后的计算方法能更好的反映边坡渐进破坏过程的应力场和变形场变化规律,并可利用特征位置点变形来判断边坡的稳定状态、根据等效剪应变的贯通来确定边坡的最不利滑动面。利用计算得到的边坡安全系数与边坡关键点位移关系曲线可以确定边坡所处的阶段,并确定其变形预警值,对于边坡的预报和防治都是非常重要的。通过多个工程实例计算发现,用改进方法计算得到的边坡变形场和位移等值线与现场实测及模型试验资料基本一致,说明根据应力水平来调整岩土体变形模量的改进计算方法用于计算边坡变形是可行的。 第五章针对目前滑动面搜索方法存在的不足,在分析用改进方法得到的土质边坡的变形场和应力场特点的基础上,研究了直接通过边坡变形场和应力场确定临界滑动面的两种方法,并用均质土质边坡和含软弱夹层粘土边坡实例对这些方法进行了验证,与传统极限平衡法相比,这两种方法既可用于确定均质边坡的滑动面,也可用于确定非均质边坡的滑动面。 第六章主要通过现场水平推剪试验和室内试验研究了边坡滑带土强度特性,包括抗剪强度指标变化规律、含水量的变化对土体强度参数、变形特点及其力学性质的影响等。研究发现,对于渐进式滑坡,坡体一般有足够的时间形成其滑动面,这类边坡的稳定性取决于其土体的残余强度,而不是峰值强度,与峰值强度相比,土的残余强度是一个比较稳定的值,且与土的初始强度没有非常明显的关系。试验结果也表明,对于岩土体而言,由于取土的扰动及小试件等室内试验条件的限制,室内试验得到的抗剪强度参数c, f值与现场试验获得的数据有一定差异,现场试验得到的结果更接近岩土体实际强度。 第七章利用具体边坡工程进一步检验前面的研究成果,结果表明,改进方法在分析边坡稳定性时,不仅可以确定边坡的安全系数,重要的是能获得边坡的渐进破坏过程,而且可给出边坡的安全储备和破坏趋势,检验结果也表明利用本文的滑面确定方法得到的最不利滑面与现场实测结果较一致。 第八章对全文的研究内容、工作方法和得出的结论进行了总结,并在本文工作的基础上提出了更待解决的问题,作出展望。 关键词:土质边坡;稳定分析;应力场和变形场;强度折减法;拉格朗日差分法

英文摘要

Some problems are present in slope research on stability analysis and deformation. Firstly, the study on stability analysis of slope is often divorced from the geology characteristic, and sites investigation is despised and destruction pattern of slope is ignored. Secondly, the popular method for stability study of slope—strength reduction method has the defect of just reducing the strength parameters not considering effects of other mechanical parameters on stability analysis of slope. Thirdly, some methods require being perfected in the current evaluation methods of slope stability, for example: the limit-equilibrium method and the strength reduction finite element method. The two methods are not related to the spot data from slope site and the deformation field and the stress field gained by numerical calculating methods. Fourthly, the“precise calculation”of evaluation methods and the calculation method are always emphasized in the research of slope stability analysis, and the importance of physical and mechanical parameters of rock and soil mass to evaluation results is frequently neglected. This paper takes soil slopes as the research object, mainly studies some problems related to the stability analysis of slope based on the deformation field and the stress field of slope, including: improving strength reduction FEM, adjusting deformation modulus according to stress level in numerical computation and analysis of slope and using it to analyze the characteristics of the deformation field and the stress field of slope, find the potential sliding surface of slope and determinate deformation warning value of slope, studying strength properties of slip soil and the methods to determine the strength parameters. Eight chapters are applied in this paper, and the concrete contents are as follows: Chapter One: The history and present situation of the research on slope stability is reviewed, and many methods for analyzing soil slope stability, including limit equilibrium method, slip line method, limit analysis method and FEM are systematically summarized, and by comparing these methods their relations and differences are analyzed. After providing the problems in current researches on stability analysis and deformation of slope, the contents of this paper are presented. Chapter Two: The mechanical background, basic features and calculation formula of the FLAC(Fast Lagrangian Analysis for Continuum ) was analysied, and the advantages and disadvantages of the FLAC method was evaluated when being applied in geotechnical engineering, and does secondary development to it and accomplish partial contents of the paper with the results of secondary development. Chapter Three: Some problems existing in slope stability analysis by strength reduction method are studied, including instability criterion, the effects of dilatancy angle changing on both the factor of safety and slip surface position of slope. Then the improvement of the strength reduction method is the stress to study. In the improved strength reduction method, not only shear strength parameters c & f, but also deformation module E, and even poissons ratio v may be reduced. The results show that the reduction of deformation module E and Poissons ratio v according to stress level of rock and soil has significant effects on the slope safety factor, principal stress difference, maximum shear strain γmax, deformation field and stress field, and plastic region of slope , etc. The calculation result shows that the reduction of deformation module E has a more significant effect on stress and strain of slope, than that of poissons ratio v. The slope safety factor decreases after reduction of the deformation module E and poissons ratio v compared to before reduction. The position of slip surface of slope changes little, but the width of slip belt of slope has obvious alteration with reduction of deformation module E and Poissons ratio v, and the plastic area of slope enlarges after reduction of deformation module E. In this chapter, the improvement of strength reduction method is achieved by means of the second development of Fast Lagrangian Analysis of Continua(FLAC2D) Software. Chapter Four: The numerical computation method using invariable deformation module E for analyzing slope stability has some problems. Based on the research results of Chapter Three and the principle of Duncan-Chang model, the old calculation methods is improved so that the deformation modulus may change with the variation of stress level of soil. Several methods for determining initial deformation module E of rock and soil are summarized, when there are difficulties to obtain the data from plate loading test. Comparing the old method and the improved method indicates that the improved method can exhibit stress field and deformation field of progressive failure slope better, and utilize the deformation characteristics of slope bodies to assess the state of slope stability, and also confirm critical sliding surface of slope by run-through plane of equivalent shear strain. The production also shows that the relationship curves between slope safety factor and the displacement key points of slope bodies may be used to ascertain the state of slope stability, which is very important for prediction and protection of the slope landslide. Through calculating several engineering cases, the results reveal that the improved method can produce the deformation field and the displacement isoline of slope bodies consistent with the results of field measured and model tests, which validates that the improved method is feasible. Chapter Five: Due to the shortages of the current methods for searching critical slip surface in slope stability analysis, three new methods based on the characteristics of deformation field and stress field of slope for searching the most dangerous failure surface of slope are presented in this chapter. The validity of those new methods is demonstrated by the homogeneous soil slopes and soil slopes with soft interlayer. Compared with the limit equilibrium method, these new methods can be applied to both the homogeneous soil slopes and anisotropic soil slopes. Chapter Six: The strength characteristic of sliding-zone soil is studied through horizontal push-shear tests in situ and shear tests in laboratory, including the change law of shear strength parameters, the effects of the change of water content on the parameters of shear strength and deformation properties and mechanical properties of slope soil. The results of tests show that the progressive landslides have enough time to form a sliding surface so that the stability of this kind of slopes depends on the residual strength, not the peak strength of soil in slide zone. Compared with the peak strength, the residual strength of soil tends to a steady value, and there are no obvious relationship between the residual strength and the initial strength of soil. The results also indicate that, for rock and soil mass, the data of shear strength of soil acquired in laboratory and in field are different, and the data from field fit better with the fact value of soil. Chapter Seven: A slope engineering is provided to verify the achievements of the research. The results reveal that the improved method can obtain the safety factor and progressive failure process of slope, and also ascertain security degree and failure trend of slope. The results also show that the critical slip surface obtained from the methods presented by this paper agrees well with the measured results in situ of the slope. Chapter Eight: The research contents and methods were summarize, conclusion is drawn., and the future study expectation is given. Keywords: soil slope; stability analysis; stress field and deformation field; strength reduction methed; finite difference method

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