【作者】 匡希龙；

【导师】 周志刚；

【作者基本信息】 长沙理工大学 ， 道路与铁道工程， 2012， 博士

【摘要】 在我国公路建设中普遍存在路基不均匀沉降现象,从而导致路基的破坏。如不能及时地采取经济、有效的措施加以解决,将造成公路建设严重的经济损失,如路面养护费用增加、使用年限缩短等。本文通过调研、室内土工试验、现场试验、离心模型试验、理论研究及数值分析的有机结合,并将混凝土结构工程中的预应力技术及弹性体高速碰撞中大变形的动力效应等相关原理引入路基工程中,跨学科进行理论上的探讨,更好地解决路基中不均匀沉降问题。即在广泛调研的基础上,对高填路堤稳定性和非均匀沉降等一系列问题进行研究分析,以室内试验、现场观测和理论分析为依托,将预应变加筋和动力强夯这两种典型的处治技术结合起来,围绕路基稳定性及非均匀沉降,科学、系统地提出其有效的控制措施。土工合成材料因其轻便、耐久、实用的特点而广泛应用于岩土工程中。使用土工合成材料加固路基,可缩短工期、降低造价、提高路基稳定性并有效延长其服务年限。但置于土中的土工合成材料长期力学性质的变化是否影响加筋土体长期稳定性,却是人们非常关心的一个问题。笔者通过对目前广泛应用于加筋土工程的土工网、土工格栅,进行了长达3年的不同应力水平作用下室内蠕变破坏试验。研究土工网和土工格栅蠕变特性及影响因素,同时探讨其蠕变断裂发生、发展直至破坏的机理,且揭示了外部荷载等级和温度变化对筋材蠕变特性的影响是有特定条件的,最后构建了土工合成材料蠕变计算模型的一般经验公式ε(t)=ε(t)=(σc/E)+(σct/η)。通过大量的实验结果分析,得出土工网、土工格栅的长期强度为抗拉强度的30%～40%。并指出在施工期及通车后各种荷载对加筋土中筋材所引起的总变形,不仅与初始应变有关,还与路堤填土高度引起的土体初始沉降及其各压缩层的正常沉降有关,同时还要考虑筋材在长期荷载作用下产生的蠕变,即加筋土中筋材所引起的总变形εi=△εi’+△εci+△εri’,而且在实际工程中得到了验证和推广。为全面推广预应变加筋法新技术,本文提出了预应变加筋法设计新思路及施工新工艺,发展了预应变加筋法的理论依据,提出了新的施工要求。首次将混凝土结构工程施工中的“反拱度”引入预应变加筋路基施工中,并就反拱度大小提出了新的理论计算公式,即反拱度δi=K0αLi(εti)0.5/2。通过数值分析进一步证实,土体变形模量和筋材拉伸模量之间的不同匹配,直接影响着加筋土的稳定效果。即土体变形模量不同,则选择的筋材必须具有相应的拉伸模量,才能充分发挥加筋效果。加筋土单元内土工合成材料的微观应力与筋材的抗拉强度、周围土体的特性及作用时间等因素有关；当加筋土单元宏观应力不变时,筋材产生应力松弛,使其单元的微观应力逐渐减小,土体单元微观应力逐渐增大,直到加筋土从粘弹性向粘弹塑性转变,单元的微观应力才会趋于稳定。基于不同的研究假设,本文进一步分析了加筋土体之间的相互作用,并从分析宏观加筋土体单元中土和筋材的微观应力角度出发,建立了基于循环荷载作用下加筋土粘弹塑本构模型,旨在为加筋土技术提供科学的理论依据。土工离心模型试验(Geotechnical centrifuge modeling)作为一种可再现原型特性的试验方法,正愈来愈受到岩土工程界的关注。本文按n=30的模型比尺进行加筋土离心模型试验,再一次揭示了土工合成材料能有效的限制土体的侧位移,阻止微裂隙的产生,从而提高了路基的稳定性。强夯法处治路基,其加固速度快、加固深度大,从而被广泛用于高速公路的路基加固,但强夯法加固机理和设计理论仍待进一步研究。本文结合工程实践,对强夯法处治红砂岩碎石土路基进行了系统研究。根据夯锤与土体的弹塑性碰撞特点,基于动力基础半空间理论,获得了强夯冲击应力和土体变形的模型,并进一步研究了影响强夯冲击应力和土体变形的因素及其规律。本文基于现场试验,借助沉降观测确定了强夯设计参数。此外,将弹性体高速碰撞中的Ansys/Ls-dyna有限元分析加以改进,引入弹塑性土体的强夯大变形的研究中,从而建立了强夯大变形的三维模型,对强夯的动力响应进行了数值模拟；揭示了强夯作用下土体的应力应变规律,建立了强夯后土体的应力场和位移场,并对比分析了理论研究结果、现场试验结果、数值分析结果,三者之间吻合较好。同时,本文通过两个实例对高填方路堤不均匀沉降预测的各种模型的拟合和预测精度进行了研究,得出双曲线和指数曲线更适合于6个月左右的中期预测,且两者中双曲线精度更高一些。皮尔曲线、灰色预测、龚帕斯曲线和皮尔神经网络方法更适合于一年以后的长期预测,且这四种预测方法中皮尔神经网络精度更高一些,灰色GM(1,1)模型的曲线拟合效果最好。更多还原

【Abstract】 At present, the phenomenon of differential settlement of roadbed is widespread in highway construction in China. Since the damage of roadbed is inconvenient to the destruction of maintenance and repair, maintenance and repair costs a lot. These phenomena show various degrees in Jiangxi and Hunan provinces. These problems will inevitably lead to serious economical loss in highway construction, for example, maintenance costs, investment waste and adverse social impacts, if they can not be settled by economic and effective measures.In this paper, through research, theoretical analysis, to combine laboratory test, Geotechnical centrifuge modeling test with field test aims to approach the theoretical study and solve practical engineering problems by cross-disciplinary approaches of prestrained technology in concrete engineering and collision theory. Namely, on the basis of extensive research, there is a comparative analysis on a series of issues the current embankment, such as, the stability and non-uniform settlement. With the helping of laboratory testing, on-site observation and theoretical analysis, around prestrained reinforcement engineering and dynamic compaction, combining lately advanced new technologies with methods of application of research, science, this paper systematically puts forward roadbed stability and settlement control of non-uniform effective method. It has a certain significance to improve the roadbed of the working conditions, the using performance of the road.Geosynthetics for its lightweight, durable, and practical characteristics in the form of reinforced soil is widely used in geotechnical engineering. Use of geosynthetic reinforcement of high filling embankment can shorten the construction period, reduce costs, improve the stability of the roadbed and the effective extension of its service life. However, geosynthetics has been placed in soil whether its the long-term changes in mechanical properties affects on solid projects stability, that concerns a lot all of us. Based on the creep experiments for geosynthetics, the creep characteristics of Netlon CE131geonet.SDL25geogrid and their influenc factors are studied for two years. Meanwhile, the mechanism of creep for Netlon CE131geonet.SDL25geogrid from occurring to be destroyed is studied too. Based on the experiments, the creep formula ε(t)=(σc/E)+(σc t/η)(in this formula σc is the stress level) for the CE131.SDL25is obtained. For the Netlon CE131geonet, when exterior load is larger than60%of the ultimate tensile strength and the temperature is higher than25℃the creep of Netlon CE131is affected apparently by the change of the temperature. And it is no longer affected by the temperature when stress level is below40%or the temperature is lower than25℃.Because lode of SDL25is not more than40%,the creep characteristics of SDL25is hardly affected. Meanwhile, the calculation model to estimate the prestrained value is also put forward (εi=△εi’+△εci+△εri’); It is important referencial value for prestrained reinforcement engineering.In order to popularize prestrained reforcement engineering, a new design thinking and construction technology are put forward. Reverse arch of concrete is applied to prestrained reforcement engineering of bed at first, a new count formula on revrese arch are put forward too, newly revrese arch δi=K0αLi(εti)0.5/2.Further confirmed by numerical analysis, soil modulus and tensile modulus of reinforcement between the different match, there is a direct impact on the stability of reinforced effect. Different soil elastic modulus reinforced slopes, a range of reinforcement tensile modulus matching to reinforcement should be chosen. A high tensile modulus of reinforcemen is used for the high elastic modulus of soil slope so that the role of reinforcement and soil is relatively more desirable properties.The micro-stress of geogrid in the reinforced soil unit is related to the tensile strength of geogrid, reinforced layer spacing, soil properties and time; When the macro-stress of reinforced soil unit unchanging, the stress relaxation of geogrid would lead to the gradually decrease of micro stress of geogrid unit and gradually increase of micro stress of soil unit, and the micro stress of unit wouldn’t tend to stable until the time of Tp while the reinforced soil arrived plastic state; The effect of model parameters of geogrid and the defqrmation and strength parameters of soil on Tp have different degrees. Based on different hypotheses, this paper analyzes the interaction between the reinforced earth and the mechanism of reinforced earth is reasonably explained; from the analysis of micro-stress of geogrid in the reinforced soil unit based on macro the reinforced soil unit, constitutive model of reinforced soil is established based on geogrid viscoelasticity in order to provide the scientific theory for reinforcemen technology.Geotechnical centrifuge modeling is deeply concerned more and more in geotechnical engineering because it is regarded as the test of revealing soil’s true features. According to modern theory of relativity on the absolute equivalence of gravity and the principle of inertia, so that1/n scale model of the geotechnical centrifuge acceleration field in the run, and to ensure that model and the prototype of the stress and strain are equal, the deformation is similar to the same failure mechanism, the prototype representation Deformation characteristics. This model by n=30for Geogrid Scale Flexible bridge model test, once again reveals the geosynthetic material can effectively limit the lateral displacement of soil to prevent the generation of micro-cracks, thus improving the stability of the roadbed.In recent years, with the rapid development of highway, the problem of improving compaction quality and decreasing post-construction settlement of embankment should be solved quickly. Dynamic compaction has been adopted to improve embankment for its wide adaptation to the soils, remarkable effects, economic building materials, low cost and short construction period etc,. However, some problems in the reinforcement mechanism and design theory still exist. Due to the shortage of the standard of design and theoretical basis of dynamic compaction, and the design of its construction parameters has been experiential(without practice) and confused. In the case, it has to be determined by means of small scope tests, so the result for the architects acts blindly and randomly. Putting the dynamic compaction into construction, crushed-stone embankment is improved by dynamic compaction is systematically studied in this paper. Considering the characteristics of imperfect elastic collision and the theory of dynamic foundation in half space, vibration equilibrant equation of hammer is established and the process of impact is analyzed. Solutions of impact stress and deformation are also obtained, furthermore, the influence factors and orderliness of impact stress and deformation are researched in theoretically. The paper determines the parameters of dynamic compaction and analyzes the strengening effect and deformation orderliness via a novelty in-situ experiment. The numerical simulation of whole dynamic process is carried out and the contours of displacement&stress are obtained with explicit dynamic finite element program Ansys/Ls-dyna. The results show that the orderliness of stress&strain are quite consistent with the experiment results and theoretical analysis results.At the same time, the prediction precision of kinds of predicting models on roadbed settlement is researched, and it can be drawn that hyperbola and index curver are more suitable for the prediction in middle period about half a year. Pearl curve、gray prediction、 Gompertz curve method and Pearl-neural network are more suitable for the long-period about a year; moreover, Pearl-neural network is the highest precision in four prediction methods, and the precision of GM(1,1) predicting model is the highest.更多还原