基于孔隙特征的反滤层设计准则研究

发布时间：2018-07-06 16:30

本文选题：孔隙特征 + 反滤准则　；参考：《西北农林科技大学》2017年硕士论文

【摘要】：世界大坝破坏实例调查结果表明,由渗透破坏而造成的大坝失事,占所有事故的40%以上。因此,土体的渗透破坏对土石坝安全影响程度很大。反滤层的使用既能保证防渗体的渗透稳定,又可充分保证排水体的排水效果,从而显著提高土石坝的安全度,由此可见对反滤层研究的重要性。现有的反滤层设计主要是从颗粒粒径的角度出发进行研究,而实际上对于被保护土是颗粒问题,对反滤层应该是孔隙的问题,也就是反滤层设计应该从被保护土的颗粒特性与反滤层的孔隙特征的对比来考察,才能真正地反映反滤保护的特征。本文以横泉水库坝体黄土为研究对象,开展了系列抗渗试验、激光粒度分析试验、压汞试验,并进行了离散元软件模拟,取得了以下几方面结论:(1)反滤层有效孔隙直径越小,被保护土的干密度越大,抗渗临界坡降就越大;将被保护黄土的抗渗强度作为因变量,反滤层有效孔隙直径、被保护土干密度作为自变量利用最小二乘法进行多元回归分析求得了两个主要影响因素的权重,为反滤层的重要性提供可靠的数据支撑。(2)现有反滤层设计中安全系数有较大的优化空间和提升潜力,在符合规范滤土排水要求的前提下,利用提出的临界坡降公式可作为预估抗渗临界水力坡降的一种手段,有效降低安全系数的取值,节省投资。(3)易流失土颗粒主要集中在小颗粒,皆位于小于被保护土颗粒级配的d50的颗粒范围内;反滤层钢珠直径越小,易流失土颗粒集中程度就越高。(4)激光法和比重计法具有良好的相关性,利用激光粒度分析仪代替传统的比重计具有可行性,而且激光法具有测量粒径范围广、重现性好、测量速度快以及操作简单的优点,为反滤抗渗试验流失土的测量提供了极大的便利,目前利用激光粒度仪测反滤抗渗试验流失土颗粒级配曲线的做法较少。(5)压汞试验主要用于测量块体内部或粉末表面的孔隙分布特性,对于测量散粒体的孔隙分布特性,目前方法还不成熟,有待进一步完善。(6)针对符合碾压式土石坝设计规范(SL274-2001)要求的反滤层采用离散元软件进行二维反滤层模拟,并加以CAD绘制孔隙,得到反滤层孔隙尺寸分布曲线。将该曲线上的孔隙直径与插值法得到的有效孔隙直径进行对比,得到有效孔隙直径为D_(孔20)。(7)在符合现有规范的前提下得到了小于0.075mm颗粒含量大于85%的粘性土基于孔隙特征的反滤层设计准则。该准则是在遵守规范的前提下对现有规范的补充,真正地反映反滤保护的本质,直观的了解反滤层孔隙与被保护土颗粒应满足的关系,可有效服务于工程。
[Abstract]:The results show that the dam failure caused by seepage damage accounts for more than 40% of all accidents. Therefore, the seepage failure of soil has great influence on the safety of earth-rock dam. The use of filter layer can not only ensure the seepage stability of seepage control body, but also fully guarantee the drainage effect of drainage body, thus significantly improve the safety degree of earth-rock dam, so the importance of research on filter layer can be seen. The existing design of filter layer is mainly from the angle of particle size, but in fact, for the protected soil is a particle problem, the filter layer should be a pore problem. In other words, the design of filter layer should be examined from the comparison between the particle characteristics of the protected soil and the pore characteristics of the filter layer, in order to truly reflect the characteristics of the filter protection. In this paper, the loess of the dam body of Hengquan Reservoir is taken as the research object, a series of impermeability tests, laser particle size analysis tests, mercury injection tests are carried out, and the discrete element software simulation is carried out. The following conclusions are obtained: (1) the smaller the effective pore diameter of the filter layer, the smaller the effective pore diameter. The higher the dry density of protected soil is, the greater the critical slope of impermeability is, and the effective pore diameter of filter layer is determined by taking the impermeability strength of protected loess as dependent variable, The dry density of protected soil is used as independent variable and the weight of two main influencing factors is obtained by using least square method in multivariate regression analysis. Provide reliable data support for the importance of filter layer. (2) in the design of filter layer, the safety factor has great optimization space and lifting potential. The proposed formula can be used as a means to predict the critical hydraulic gradient of impermeable soil, which can effectively reduce the value of safety factor and save investment. (3) the particles of easily runaway soil are mainly concentrated in small particles. The smaller the diameter of the steel beads in the filter layer, the higher the concentration of the particles in the easily lost soil. (4) there is a good correlation between the laser method and the hydrometer method. It is feasible to use laser particle size analyzer instead of traditional hydrometer, and laser method has the advantages of wide range of particle size measurement, good reproducibility, fast measurement speed and simple operation. It provides great convenience for the measurement of soil loss in filtration and impermeability test. At present, there are few methods to measure particle gradation curve of lost soil by using laser particle size meter. (5) Mercury injection test is mainly used to measure pore distribution characteristics of bulk or powder surface, and to measure pore distribution characteristics of granular body. At present, the method is not mature and needs to be further improved. (6) according to the design code of roller compacted earth-rock dam (SL274-2001), the filter layer is simulated by discrete element software, and the pore is drawn by CAD. The pore size distribution curve of filter layer is obtained. The pore diameter on the curve is compared with the effective pore diameter obtained by interpolation method. The effective pore diameter of D _ (pore 20). (_ 7) is obtained and the design criteria of filter layer based on pore characteristics of cohesive soil with less than 85% 0.075mm particle content are obtained on the premise that the effective pore diameter is D _ (20). (_ 7) in accordance with the existing specifications. The criterion is a supplement to the existing code under the premise of complying with the code, which truly reflects the essence of filter protection, and intuitively understands the relationship between the pore of filter layer and the particle of protected soil, which can effectively serve the project.
【学位授予单位】：西北农林科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TV640.33

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