【作者】 陈西安；

【导师】 王保田；

【作者基本信息】 河海大学 ， 岩土工程， 2007， 硕士

【摘要】 渗透破坏是江河大堤在汛期的常见险情之一。在病险堤坝的处治过程中，形成了一些比较成熟的治理技术，积累了丰富的经验。垂直防渗技术已广泛用于堤坝的除险加固，是病险堤坝的主要防渗加固措施。防渗墙是垂直防渗技术中的一种，按其结构型式可以分为三类：封闭式、半封闭式和悬挂式。长江中下游地区堤防防渗现状研究成果表明，长江中下游堤基大多为二元结构且多为深厚的软弱土，缺乏可靠的防渗措施。长江中下游堤防虽经历代帮宽加高，仍存在着堤身土质杂乱、压实度小、填筑质量差、防洪标准低、堤基严重渗漏、岸坡冲刷、人类活动及生物破坏严重、穿堤建筑物年久失修且严重老化、堤防长期持续沉降等隐患。本文结合长江中下游堤防堤基的特点，制作了渗流槽来模拟二元结构堤基的渗流特点，进行了系统的室内试验，讨论了悬挂式防渗墙在阻滞二元结构堤基土发生渗透破坏中的作用。试验用土取自长江堤防南京段长江南岸，上层为粉质粘土，下层为粉土。试验用土与现场土是一样的，这样试验过程和堤基发生渗透破坏的水力要素是一致的。对粉土和粉质粘土进行了以下试验：比重、颗粒分析、液塑限、渗透系数。试验结果表明，粉土缺乏中间粒径，颗粒级配不良，易于发生渗透变形。粉土的渗透系数与粉质粘土的渗透系数相差20倍，在汛期高水位作用下，在粉质粘土层的底部容易形成较大的水头压力，从而导致险情的发生，因此有必要采取有效措施来阻滞险情的发生与发展。根据长江堤防堤基土的特点，制作了渗流槽模型，渗流槽用有机玻璃制成，其尺寸为：长2米，高1米，宽10厘米。将粉土和粉质粘土装入模型槽，模拟二元结构堤基土发生渗透变形的特点以及研究悬挂式防渗墙在阻滞堤基土发生渗透变形中的作用。模拟试验通过改变粉质粘土组成的悬挂式防渗墙的入土深度来模拟实际渗出比降情况。由于土的级配、干密度等与现场土的相同，临界水力梯度和抗渗效果等与现场一致。室内试验过程中，分别进行了没有悬挂式防渗墙，不同防渗墙深度时堤基土的渗流变形特性试验。对于上部为粉质粘土，下部为粉土的二元结构堤基，发生渗透变形时首先在粉土层的薄弱部位发生涌砂，接着在粉质粘土层与粉土层的结合层面发生接触冲刷，在水位持续升高，超过了临界水位后，渗透通道从下游向上游发展而贯通，即发生渗透破坏。同时，研究发现在悬挂式防渗墙作用下，堤基土发生渗透破坏的条件有明显改善，表现在渗透破坏时的作用水头有较大的增长，临界表观水力梯度有明显提高，渗流量显著减小，以及孔隙水压力的变化。研究结果表明，悬挂式防渗墙可以有效控制渗透破坏的发生条件，而且施工相对容易，也比较经济合理，可以在工程中推广应用。更多还原

【Abstract】 Seepage failure is one of the high frequent disasters for dike engineering during flood season. At present, a number of ripe vertical cut off techniques have been widely used in levee project, and many rich experiences have been accumulated in the treatment of diseased levee project. The vertical seepage controlling technique has been widely used in levee project, and it is the main reinforcing methods for seepage preventing. The seepage controlling wall is one of the techniques of vertical seepage controlling method, and it can be divided into three types: closed seepage controlling wall, semi-closed seepage controlling wall and suspended seepage controlling wall.The research of seepage preventing indicates that the foundation of the middle and lower reaches of Yangtze Rive is mostly composed of dual subsoil layers which is often soft clay and lacks reliable methods to prevent seepage. The middle and lower reaches of Yangtze Rive has been widen and reinforced, but there are still some hidden troubles, for example, disorder embankment soil, small degree of compaction, lower construction quality, lower criterion of controlling flood, serious leakage of dike foundation, sever eroding of embankment slope, badly destroyed by the human being, demolishing and aging of the buildings that across the embankment, long-time and continuous settlement and so on.On the basis of the characteristics of the middle and lower reaches of Yangtze Rive, a seepage sandbox has been made to simulate the specialty of the dual subsoil layers. The tests have been done indoors and the functions of suspended seepage controlling wall in preventing seepage failure have been discussed. The following are the main contents.The soil that is used in the test is from the south bank of NanKing dike of Yangtze Rive. The upper layer is composed of silt clay and the under layer is composed of silt. The soil is same to that of the local spot, so the hydraulic factors of seepage failure is also the same. The tests of the two kinds of soil have been carried out which are specific gravity, coefficient of permeability, particle size analysis, liquid limit and plastic limit. The results indicate that the silt lacks middle particles and the particle size is symmetrical which can easily leads to seepage deformation. The hydraulic conductibility of silt is 20 times that of the silt clay. Under the function of high water level during flood season, great hydraulic pressure can be easily produced under the bottom of the silt clay layer which can cause some disasters to happen. So, some effective measures must be taken to prevent dangers.Based on the foundation characteristics of Yangtze Rive embankment, a seepage sandbox has been manufactured which is made of plexiglass. It is 2 meters long, 1 meter high, and 10 centimeters wide. Silt clay and silt are put into the sandbox. It can be used to analyze the characteristics of seepage failure and the function of suspended seepage controlling wall which is used to prevent seepage failure. The actual hydraulic gradient is simulated by changing the deepness of the suspended seepage controlling wall which is composed of silt clay. The mechanical composition and dry density of the soil are same to that of the local spot, so the critical hydraulic gradient and the effect of preventing seepage are consistent with that of local spot.During the time of the tests indoors, the tests which have different depths of suspended seepage controlling wall have been done. For the dual subsoil foundation which are composed of silt clay upside and silt subside, sand spring occurs at the feeble spots, then contact erosion occurs at the face that silt clay and silt integrate. When the water level rises continuously and exceeds the critical water level, the seepage channel develops from downstream to upstream, and runs through the whole soil. At this time, the seepage failure occurs. Research indicates that under the function of suspended seepage controlling wall, the qualification of seepage failure has been improved, for example, the water level rises greatly, critical apparent hydraulic gradient increases obviously, the seepage quantity reduces distinctly and the pore-water pressure changes evidently. The results of the research are that the suspended seepage controlling wall can effectively block the seepage failure, at the same time, it is constructed easily and acceptable in economy, so it is worth applying in project.更多还原