【作者】 冯晓静；

【导师】 杨庆；

【作者基本信息】 大连理工大学 ， 岩土工程， 2009， 博士

【摘要】 在土中加入一定的抗拉材料而形成的加筋土工结构,可以起到有效提高岩土构筑物的稳定性、防渗性、排水性、防冻性及隔离污染等多种作用.尽管目前加筋土结构的应用在数量上和规模上都是史无前例的,但是关于加筋结构工作机理尚未得到清楚的认识,设计理论和方法还远远落后于工程实践,缺乏严密的分析理论与计算方法。边坡失稳是路堤等岩土构筑物的主要破坏形式,研究和实践证明加筋边坡可以提高其稳定性,然而影响加筋边坡的因素众多,要想合理布置而更加有效地起到加固土体的作用就需要抓住重要因素,忽略次要因素,因此有必要对影响加筋边坡稳定性的因素进行敏感性分析,本文基于塑性极限分析的上限定理对该敏感性问题进行了分析研究。一直以来,粒状填料在加筋土结构中一直予以推崇,规范中也建议使用粗粒土,然而我国幅员辽阔,地质条件千变万化,在缺乏优质填料的区域,一味地追求填料性质往往会造成过量投资,因此研究细粒土尤其是黏性土填料的加筋结构特性将大为有利加筋土结构的推广和应用,节约大量的占地和人力物力,为国家谋取更大的社会效益和经济效益。本文利用大型拉拔仪,对土工格栅在红黏土中的拉拔特性进行了试验研究。另外拉拔力的有效预测是加筋结构准确设计的必要条件,根据试验资料以及以往的分析方法,本文对土工格栅在黏土中的拉拔荷载预测提供了新的计算方法。另外,加筋支挡结构中常用的面板,目前实际使用的类型很多,然而人们在设计中很少考虑不同面板对于加筋结构性状的影响,本文根据已有的面板类型,在室内制作了模型,并通过模型墙试验分别研究了各类面板对挡墙承载力和变形特性的影响。具体地,论文的主要研究内容和取得的成果包括以下方面:(1)加筋陡坡临界高度的影响因素敏感性研究基于塑性极限分析的上限定理,利用自编程序分别计算了不同坡脚、顶面倾角、内摩擦角、粘聚力、筋带抗拉强度、加筋间距、加筋形式、填土重度、地震烈度、顶部荷载共10种影响因素作用下加筋陡坡的临界极限高度。根据正交分析方法给出了各个因素的敏感性顺序,结果显示土的内摩擦角和地震作用对陡坡临界高度的影响最为显著,粘聚力敏感性则较缓坡有所下降。因此对陡坡应重视对土的内摩擦角的选取,并在设计中对地震作用予以重视。(2)土工格栅加筋路堤的现场试验研究本文对黑河至大连一级公路榆树至大口钦段的加筋路堤进行了现场试验测试分析,试验分别对两种格栅类型,三种不同加筋间距等工况下的土压力、格栅应变、路堤沉降进行了现场观测,研究了加筋层数及加筋类型对路堤结构性能的影响。通过试验结果的比较分析,探讨了包裹式柔性支挡结构的土压力分布规律;格栅应变沿筋带的分布及其随时间的变化规律。同时,加筋对于控制土体沉降,限制冻胀的作用在试验中也进行了探究。试验显示了加筋路堤的真实工作状态,结果为土工格栅加筋结构的后续研究和工程实践提供参考。(3)土工格栅在红黏土中的拉拔试验研究及拉拔阻抗的预测通过室内大型拉拔试验设备对土工格栅在黏土中的拉拔特性进行了系统测试,测试结果发现土工格栅在黏性填料中主要表现为拔出破坏,含水率对拉拔力的影响显著,拉拔极限荷载随含水率的增加逐渐降低,在塑限附近趋于一常数,且此时土的拉拔力与法向荷载关系不大,即格栅与填料之间的似摩擦系数接近0。格栅的应变分布特征证明含水率的增加导致筋土摩擦力的显著减小。停止加载后,格栅应变在土中会进行重分布,结果横肋应变增大,而纵肋应变减小。含水率除了影响极限拉拔力,还影响格栅的拉拔过程。拉拔力-位移关系曲线大致可以分为三个阶段,线性上升阶段、非线性上升阶段以及极限承载力阶段,随着含水率的增加,第二阶段逐渐缩短,即格栅的线性增长结束后很快达到极限承载力。目前规范中关于拉拔阻抗的计算仍然是在土料的内摩擦角基础上乘以一个折减系数而获得,此法简便实用。而要使得极限拉力的预测更加精确则应该寻求更为合理且有效的方法。本文基于拉拔阻力来自横、纵肋的摩擦与横肋阻隔作用的叠加,对各部分抗力作用分别予以计算,并根据试验数据拟合得出了红黏土中拉拔阻抗计算的公式及其随含水率的变化。(4)挡墙面板刚度对土工格栅加筋挡墙工作特性影响的模型试验研究目前用于加筋土结构的设计方法仍然基于极限平衡设计理论,在普通结构的基础上考虑筋带提供的拉力作用,而加筋土结构的面板在设计方法中并不予考虑,部分研究证明这会导致设计偏于保守。根据目前实际工程中常用的几种面板类型,本文在室内制作了模型面板包括一个混凝土模块式、一个铰接式和一个格栅包裹式,并在试验槽内实施了加筋土挡墙模型试验,顶部加载采用局部加载的方式,试验结果显示面板刚度越大,同样附加荷载下挡墙面板的变形越小,格栅的应变也会更大。此外,面板类型还影响应变沿格栅的分布。结果说明面板刚性越大,挡墙的承载力也将越大,但是破坏时的延性却会变差。更多还原

【Abstract】 Reinforced structures formed by bringing the tension material into the soil can improve the stability,anti-seepage,drainage,anti-freezing and insulate the contamination effectively. Although the application of reinforced structures has been tremendous both on the quantity and scope currently,the deformation behaviour and working mechanism of reinforced earth structures have not been well understood and rational analysis theory and design methods for these structures are not available.Sliding damage is the main failure mode of the slopes, researches and practices indicated that the reinforced slopes can improve the stability evidently. However,there are many influence factors so that it is necessary to do the sensitivity analysis to determine which ones are the principal factors and which ones are the secondary factors.It will contribute to focus on the most important factors to achieve the optimum arrangement.In this paper,the upper bound limit analysis method is used to probe into the sensitivity of influence factors that affect the limit height of reinforced slopes.Coarse-grained soil is always recommended for the reinforced structures both by standards and other manuals.Whereas China is vast and complicated in territory,geological conditions are various among different district,it will be not reasonable and economic to only use the coarse-grained soil in the area which be lack of this kind of fills.Therefore,the research on the application of reinforced structures using fines especially for clay must be significantly.This paper presents the research of pullout behavior of geogrid embedded in red clay.An experimental investigation is conducted using geogrid tests of eight different moisture content of the soil.Effective predication of the ultimate pullout resistance is a necessary condition for the design of reinforced structures.Based on the results of experiment and analysis method proposed by Koerner in 1989,a new method to predict the pullout resistance applicable to clay fills.Wall facing is an indispensable part in the retaining walls,but it is never considered in the design. The researches indicates that the wall facing can induce the design inclined to be conservative. According to the real wall facing used in practice,three model facing were made in the laboratory.The influence on the behavior of model retaining walls including displacement of facing,deformation of the geogrid and the ultimate bearing capacity from wall facing were tested in this paper.The main investigations and achievements are composed of following portions.(1)Studies of sensibilities of influence factors on critical height ofreinforced steep slope Based on the fundamental theory of upper-bound limit analysis of plasticity,the limit heights and stability coefficients of the reinforced steep slopes with different slope angles,top slope angles,internal friction angles,cohesive,reinforcement tension strengths,reinforced spacing,reinforcement arrangement,unit weights,seismic intensities and additional loads are calculated based on a code written by the authors.The sequence of sensibilities is listed;and the results show that the internal friction angle and earthquake are the key factors that influencing the critical heights of the reinforced steep slope.Whereas,the sensibility of cohesive is descend contrast to the gentle slope.Therefore,the emphasis should be placed on the selection of the internal friction angle for steep slope and the effect of earthquake as well.(2)Field experimental research of geogrid reinforced embankment.This paper reports the results of field experiment on geogrid reinforced embankments constructed on a part of first-order highway from Heihe to Dalian.In the test,The structural responses including earth pressures,geogrids strain,and settlements on pavement are investigated for the reinforced embankments with two geogrid types,three different reinforcement spacing and one district without reinforcement.Based on the contrast analysis, the distribution of earth pressure behind the flexilbe facing and the geogrid strains with height or reinforrnent layer,and their dependence on the time are discussed.Also the influence of the reinforcement on the settlement and its restriction to the frost heaving of the soil are given.In general,this experiment reveals the embankment’s real work condition,and the results showed here gives a good reference for the succeeding research and the similar engineering.(3) Pullout behavior of geogrid in red clay and the PredictionThis paper presents a research of pullout behavior of geogrid embeded in red clay.An experimental investigation is conducted under eight different moisture content of the soil.Tests results indicate that the geogrid mainly represents pullout failure embedded in clay,and the ultimate resistance is water-sensitive.It decreased with the rise of the moisture content firstly, and then tended to a constant around the plastic limit where the ultimate pullout force is independent of the normal pressure.The display of strain demonstrates that the decrease of the ultimate pullout force is due to the reduction of the friction capability between the soil and geogrid.Besides this,the moisture content influenced the process of the pullout behavior as well.The load-displacement curve can be separated into three parts:linear ascending segment, nonlinear ascending segment and ultimate segment,the increase of moisture content shortened the second segment,which means that the ultimate pullout force will be reached soon after the end of the first segment.The prediction of the ultimate resistance in current standard is depend on the internal friction angle times a ratio to simulate the interaction between reinforcement and soil.While the more accurate prediction needs more consideration.This paper based on the ultimate pullout resistance comes from three parts those are friction resistance from longitudinal and transverse ribs and the bearing resistance from transverse ribs.According to the results of experiment,each part was calculated individually and the prediction equation changed with moisture content was obtained.(4) The influence of facing stiffness on the performance of three geogrid reinforced soil retaining model wallsConsideration of the influence of the facing type on reinforcement loads is lacking in current limit equilibrium-based design methods for the internal stability design of geosynthetic reinforced soil walls.Also the displacement of walls and the strain of geosynthetics are also related to the facing type.This paper reports the results of the three instrumented model walls. The walls were nominally identical except one wall was constructed with a rigid concrete block face,the other with a hinge joint wood face,and another with a flexible wrapped face.The displacement of wall face decreased with the increase of the stiffness of wall facing under the same surcharge.And the reinforcement strain in the flexible wall will be greater than the stiff one.Besides this,the stiffness of wall face also effects the strain distribution of each level.The results demonstrate quantitatively that a stiff facing wall can bear more surcharging but it expressed as brittle failure.更多还原