【作者】 张伟；

【导师】 茜平一；

【作者基本信息】 武汉大学 ， 岩土工程， 2004， 博士

【摘要】 非饱和渗流问题、堤防的渗透控制措施的优化以及渗流场和应力场的相互影响和耦合计算问题是岩土工程学科发展中很重要的一个方面。非饱和渗流是非饱和土力学重要研究内容之一，许多非饱和土问题都与流量边界条件下非饱和土体中的暂态渗流情况有关，对非饱和渗流进行系统的研究无论在理论上还是在工程应用中，都具有十分重要的意义；我国的河道堤防非常的多，其发生破坏的原因在很大程度上是由于渗流问题引起的，对堤防的渗流控制方案进行研究和优化是很有必要的；渗流场和应力场是岩土工程力学环境中的最重要组成部分之一，二者之间是相互联系、相互作用的，岩土介质的渗流场和应力场的相互影响体现了两场之间的耦合关系，把渗流场和应力场作为一个系统，研究和探讨渗流场和应力场的耦合问题，也是十分有必要的。 本文在总结前人研究成果的基础上，主要研究和探讨了以下四个方面的内容：饱和非-—饱和、稳定—非稳定渗流计算的有限元分析；堤防渗控措施的比较和优化；土体湿化以及湿化变形的计算；土体渗流场和应力场的耦合计算问题。 1．阐述了土体的土水势理论；对非饱和渗流的基本理论、土—水特性曲线和渗透系数的关系以及材料非饱和渗透参数的确定等进行了研究和探讨； 2．从渗流基本理论出发，以压力水头为基本未知量推导多孔介质三维饱和—非饱和、稳定—非稳定渗流问题的微分方程以及方程的有限元格式；在饱和非饱和渗流场的有限元分析中，不仅考虑了饱和区的水体渗流情况，而且也考虑了非饱和区的水分运动情况，将饱和渗流场与非饱和渗流场统一起来进行研究，整个渗流场采用一个支配方程。 3．利用三维饱和非饱和渗流有限元程序，对工程算例进行了计算，对水位发生上升和下降的变化时渗流场的变化情况进行了分析和探讨。可知：随着水位的上升，负压区的范围变小，饱和区域的孔隙水压力变大，部分土体由非饱和状态变为饱和状态，零孔压线的上升和水位的上升相比，存在着滞后的现象，孔压等值线的局部区域变陡，局部区域孔压变化梯度比较剧烈，水力坡降增大；而且在负压区局部区域，孔压等值线变得密集的现象比较显著；水位上升越快，土体的渗透系数越小，这种滞后的现象越明显；上游水位上升对坝体中靠近下游的区域的影响相对于其它的区域要小。上游水位下降，负压区的范围变大，正压区的范围和孔隙水压力变小，上游坝坡附近出现了顺坡向上游的渗流，水位下降越快，土体的渗透系数越小，顺坡渗流越明显，上游坝坡附近的水力坡降就越大，由此产生的顺坡向的渗流动水压力也越大，对坝体的渗流稳定的威胁也越严重。 4.介绍了堤防渗透控制的主要内容、垂直防渗和水平防渗的措施;对堤防工程堤基的类型、堤防工程渗流的特点进行了分析，研究和探讨堤基渗透性能的各向异性和堤基表层的薄弱透水覆盖层厚度对渗流场的影响。堤基和堤身渗透性能的各向异性，造成渗流进出口水头等势线密度大，剩余水头比较大，渗流场中浸润线的位置升高，渗流出逸点的位置也相应地被抬高;随着弱透水覆盖层厚度的增加，背水侧堤脚的剩余水头和出逸比降变小，使得堤防容易达到安全状态的要求，有利于堤防的渗透稳定。 5.分析了在堤基为上强下弱、堤基为深厚的强透水层等多种情况下，各种垂直防渗墙(全封闭式防渗墙、半封闭式防渗墙和悬挂式防渗墙)的适用条件和防渗方案的优化等，同时探讨了防渗墙的渗透系数对防渗效果的影响。 结果表明:全封闭式防渗墙的防渗效果显著，但因其工程造价高，一般只能在堤基的强透水层不厚的情况下采用; 透水堤基上设置悬挂式防渗墙时，防渗墙的影响范围有限，防渗作用不大，在实际的应用中，悬挂式防渗墙经常和其它的水平防渗措施相结合; 半封闭式防渗墙必须与多元结构的堤基结合才能组成合理的防渗体系，适合于有弱透水夹层的深厚型强透水堤基，防渗依托层是评价半封闭式防渗墙技术可靠性的关键因素，防渗依托层应该是连续的、有足够的厚度和足够小的渗透性; 防渗墙的防渗效果取决于防渗墙与土体渗透系数的比值。 6.阐述了土体的湿化变形以及湿化变形产生的机理，对湿化变形的计算方法作了一些探讨; 结合算例，采用非线性弹性模型，对土体的分级加荷、土体湿化所引起的应力场、位移场的变化等进行了分析。 土体湿化以后，考虑土体的湿化变形作用，浸水区域的应力和应力水平明显降低，算例中湿化前后浸水区域底部最大的主应力的差别几乎达到50%，浸水区域湿化前后的应力水平的差异也比较显著;土体浸水以后，位移场也发生了变化，水平位移和竖直位移变大，水平位移和竖直位移最大值分别增加了20%和10%左右。 7.以达西定律、质量守恒定律等为基础，推导出了考虑孔隙比变化的非稳定渗流场的微分方程和有限元方程; 探讨了渗流场和应力场的相互作用的藕合机理，针对应力场对土体孔隙率的影响、渗流场引起的应力场的变化等进行了量化的分析，探讨了考虑应力场变化影响的渗透系数的计算方法; 考虑渗流场和应力场的相互作用，得到岩土介质渗流场和应力场祸合的数学?更多还原

【Abstract】 The unsaturated seepage problem, the optimization of seepage control measure to dykes and the interaction and coupling between seepage field and stress field are the importance problems in geotechnical engineering. The unsaturated seepage problem is one of the important studies of the unsaturated soil mechanics. Many unsaturated soil mechanics are related with the transient seepage of unsaturated soil under the flux-boundary. Considering the theory problem and engineering appliance, it is very significative for us to make a systematic study. Because there are many riverway-dyke projects, whose breakage reasons mostly ascribe to the seepage, it is necessary to research the seepage-control case and optimization. Seepage field and stress field are the most important composing-parts of geotechnical engineering mechanics. The interaction between seepage field and stress field of rock and soil medium embody the coupling relation between two fields. Considering two fields as a system, it is also essential to research and discuss the coupling problem between seepage field and stress field.Being based upon summarizing the existing research, this thesis mostly covers the Finite-Element Modeling of the saturated-unsaturated and steady-unsteady seepage, the compare and optimization of dykes-seepage measure, soil slaking and its displacement-calculation, the interaction and coupling between seepage field and stress field.1. This thesis first introduces soil moisture potential theory, then research and discuss the basic unsaturated seepage theory, the relation of soil-water’s characteristic curve and seepage coefficient and the confirmation of the material unsaturated seepage coefficient.2. Beginning basic seepage theory, thesis introduce the 3D saturated-unsaturated and steady-unsteady seepage differential equation of porous media and the FEM regarding pressure water head as basic unknown quantity. On the saturated-unsaturated seepage field FEM, both the seepage in the saturated area and the hydrodynamic effect in the unsaturated area are considered, unifying saturated-unsaturated seepage field andapplying uniform derivative governing equations in the wholly seepage field.3. Applying the 3D saturated-unsaturated FEM program and calculating one project instance, the change of the seepage when water head rises and descend also are researched and discussed. That shows that with the water head rising, negative pressure area reduces, pore water pressure in saturation area enlarges, partly soil changes from unsaturated status to saturated status and the area matric suction loses or minishs. During the water head rises, zero pore water pressure-line rises lagging hysteresis effect comparing to the rise of water head, pore water pressure isoline becomes abrupt on the local region, the grads of pore water pressure in local area are marked and waterpower slope-drop enlarges. Moreover, pore water pressure-isoline becomes evidently denseness in local negative pressure area. The more rapidly the water head rises and the smaller the seepage coefficient is, the more evident the lag is. The rise of the upriver water head has little effect on the midland close to backward position of the dam. Upriver dam has seepage along the slope. The more rapidly the water head descend and the smaller the seepage coefficient is, the more evidence the lag and seepage along the slope are, and the greater the waterpower slope-drop at the upriver dam slope is, correspond to which the greater the seepage hydrodynamic pressure along the dam slope and the more the seepage-steady in the dam is affected badly.4. Dyke seepage control, upright defence seepage and horizontal defence seepage are introduced. The style and the specialty of the dyke foundation are analyzed. The anisotropism of the penetrability in soil layer and the effect of the thickness of surface overcast low penetrability layer are researched. Anisotropism of the penetrability of dam and foundation material arouses that the density of the equipotential line of water head at entrance en更多还原