【作者】 周红星；

【导师】 曹洪； 莫海鸿；

【作者基本信息】 华南理工大学 ， 结构工程， 2011， 博士

【摘要】 堤防是世界上历史最悠久的防洪工程措施,也是防御洪水的最后一道屏障,其重要性不言而喻。而堤基渗透破坏在以往以及可预见的岁月里,仍将是堤防工程的最直接和最大的威胁。尽管对堤基渗透破坏的研究在以往取得了一定的成果,但仍对其产生、发展(包括渗流出口的形成)规律的缺乏深刻认识,使得堤防工程的实践多依靠经验。因而,本文针对双层堤基渗透破坏发展过程进行了以下几个方面的工作:1.双层堤基渗透破坏试验技术研究针对双层堤基的特点,对试验装置和方法进行了研究。制作了适合双层堤基特点的试验装置。对模型试验的比尺进行了分析。针对当前堤基渗透破坏模型试验中缺乏对覆盖层的影响研究,着重分析了不同覆盖层与下卧砂层接触性质,并根据试验结果,指出了分析了有机玻璃、水泥砂浆、密闭柔性水袋三类覆盖层模拟材料对堤基渗透破坏发展、上溯的影响,认为覆盖层的作用不仅起到隔水的作用,也体现到对下卧砂层的约束作用,而后者往往被忽视。考虑到渗流出口是渗透破坏的必要条件。因此,根据双层堤基典型断面,研究了在试验中如何实现覆盖层薄弱区的模拟,提出了通过改变模拟材料的配比达到对覆盖层性质的控制。2、双层堤基渗透破坏过程试验研究。这项研究主要有两部分:1)渗流出口形成过程试验研究通过改变堤后覆盖层薄弱区不同尺寸,研究堤后覆盖层在下卧承压水作用下形成渗流出口的一般规律。同时还研究了覆盖层薄弱区土层厚度和土体性质对其破坏规律的影响。2)双层堤基渗透破坏发展、上溯试验研究首先,采用水泥砂浆为覆盖层模拟材料,对渗流出口砂沸和集中渗流通道形成过程进行了一般规律的试验研究。其次,对膨润土、柔性水袋两种覆盖层模拟材料进行了对比试验研究。最终,从试验研究中认识堤基渗透发展上溯的实质和规律3、渗透破坏发展过程机理研究基于试验研究结果,对渗流出口状态进行了分析,指出渗流出口是渗透破坏的必要条件,没有渗流出口就没有渗透破坏。以试验为基础,研究了堤基渗透破坏发展、上溯的内在因素的影响,提出了堤基渗透破坏发展过程的最终型式为土体整体破坏,其实质是土体抗渗强度与渗流强度相互作用的结果。基于对渗透破坏发展上溯过程机理的认识,提出了考虑渗流力以及土体应力环境下土体渗透稳定判据,以及考虑土体运移稳定的泥沙动力学平衡判据。考虑到堤基渗透破坏区域较小,堤基大部分区域仍按满足达西定律的稳定渗流场计算。同时,将集中渗流通道做为渗流场的边界条件处理。根据等效水力半径将集中渗流通道简化为半圆形变截面通道,按照水力学管流特点给出水头和流量关系。4、数值模拟研究1)渗透破坏发展过程数值模拟研究依据对渗透破坏发展实质的认识,并基于破坏区域相对堤基整个区域较小的特点,采用二维轴对称有限元计算土体渗流场。取以渗流通道走向纵剖面为计算面,采用二维平面应变法计算应力场,并结合提出的两个判据,对堤基渗透破坏发展过程进行数值模拟计算,计算结果与砂槽试验结果相近,表明该方法是可行、合理的。应用双层堤基渗透破坏发展有限元程序对双层堤基进行数值模拟研究,提出了“无害管涌”的准确含义。2)覆盖层破裂数值模拟研究根据试验观察和分析认为,双层堤基覆盖层在承压水作用下形成渗流出口的过程其实质就是裂缝出现、发展的过程,提出了基于的断裂力学理论基础,采用扩展有限元法对覆盖层破坏进行数值模拟,由此对这方法在参考文献的基础上进行了研究,并开发线弹性二维覆盖层裂缝扩展有限元程序。数值模拟结果与试验对比表明该方法是可行、合理的。应用上述程序对覆盖层在承压水作用下开裂,以及裂缝扩展过程进行了数值模拟,其结果表明:薄弱区周围,即堤脚部位是最可能发生渗透破坏的部位。实际工程中,仅增加覆盖层压重,尽管提高承压的能力,但使得破坏形式发生改变,出现破坏很突然。这对汛期抢险工作极为不利。更多还原

【Abstract】 Dike is the world’s oldest flood control engineering measures. And it is the last line of flood protection. The importance of dike engineering is self-evident. Seepage failure, in the past and for the foreseeable years, was and will be the most direct and biggest threaten to the dike. Although the research on seepage failure made a little progress, the general law of seepage failure is still not enough to be recognized. To improve the awareness of seepage failure of double-layers foundation of dike, the following jobs are carried out in this dissertation:1. Research on the experimental technique of model test. According to the characteristics of double-layer of dike foundation, the test apparatus is designed and the method is studied. The scales of model test are analyzed.In view of the lack research on the impact of overburden layer on the development of seepage failure, the nature of contact between the different simulating materials and sand is emphatically analyzed. According to the test results, the effection of the covering layer is not only impervious. The stress effection is also not neglected.Considering the seepage exit as the necessary condition of seepage failure, how to simulate the weak spots of the overburden layer is studied. By changing the ratio of compositions, the characteristic of overburden layer is controlled.2.Experimental research on the seepage failure.1) Experimantal study on the formation of seepage exitBy changing the size of the weak spot of the overburden layer, the general law is studied on the formation of seepage exit. Also the effection of the properties and the thickness of the covering layer on the formation of seepage exit are researched.2) Experimatal research on the development of seepage failureFirst, using cement mortar as the covering layers, progress of the seepage exit and concentrated seepage channel are analyzed. Secondly, results of experiments, using the bentonite and seal flexible water bag as the overburden layer, are compared. The effection of overburden layer on the seepage failure is analyzed.3. Research on the mechanism of seepage failure Based on the experimental results, the mechanism of formation of seepage exit is analyzed. It is pointed out that the seepage exit is the necessary condition of seepage failure.According to the results of experiments on the development of seepage failure, the influence of the inner factors on the seepage failure is studied. It is put forward that the final failure model of seepage failue is flow soil. The development of concentrated channel is the result of interaction between the anti-permeability of soil and seepage strength. Based on understanding of the seepage failure mechanism, two criterions are derivate. One is the stress strength, considering the seepage force. The other is the limited balance of the rotational moments of soil particle.Considering the failure zone is lesser, Darcy law is still satisfied on the most of the region. Meanwhile the relationship between the water head and flow is available throught the hydraulic method.4. Research on numerical simulation1) Numerical simulation on the progress of seepage faiure Based on understanding of seepage failure mechanism, the seepage field is computed by axisymmetric FEM. Compared the results between the experiment and numerical simulation, the above research method and two criterions on the seepage failure are reasonable, feasible.By applying of above program on the simulation of seepage failure, the precise definition of“harmless piping" is put forward.2) Numerical simulation of seepage exit formationAccording to the experimental observation and analysis, the formation of seepage exit is result of cracking and expansion. Based the theory of fracture machanics, the formation of seepage exit may be simulated by the extended finite element method. And on the basis of the references, the program of linear elastic 2-D extended finite element is developed. Compared the results between the experiment and numerical simulation, the above research method are reasonable, feasible.更多还原