PP织物袋在陕北淤地坝渗透破坏治理中的试验研究

发布时间：2019-06-21 06:26

【摘要】：淤地坝是小流域综合治理的重要水保工程措施之一,既可以增加耕地面积、提高农业生产力,又可以防止水土流失。上世纪70到80年代由于当地砂石料缺乏,建设经费不足,陕北靖边、定边地区所建淤地坝绝大多数未布设反滤材料,导致淤地坝产生渗透破坏而成为病险坝,这一问题目前一直未得到很好地解决,给当地淤地坝工程带来严重的安全隐患。坝后渗透破坏已成为制约当地淤地坝建设的一个重要问题。论文以陕西省榆林市靖边县高家沟乡淤地坝的筑坝土料粉砂质壤土为研究对象,通过室外模拟原淤地坝在渗流作用下的渗透破坏现象及过程,并用PP织物袋装填原状土作为反滤体对比其对渗透历时和浸润线的影响。对渗透破坏之后的坝体土样用扫描电子显微镜研究坝体土样的微观结构和孔隙特征,用马尔文激光粒度仪分析渗透破坏过程中的渗流泥沙颗粒级配,分析PP织物袋对渗透破坏的防治效果,为陕北靖定地区产生渗透破坏的淤地坝进行除险加固提供理论依据和技术支持,该项研究具有重要的工程实践意义。本论文的主要结论有:(1)筑坝土料的常规土工试验结论试验分析结果表明,该筑坝土料属于中粉质壤土,土样类别为低液限黏土。土料粒径分布不均匀,不均匀系数CU=6.12,CC=0.90,不能同时满足CU5及CC=1~3的条件,因此属于不良级配的土样,土壤较大土粒间的孔隙在渗流的作用下可被较小土粒较容易通过而造成渗透破坏。(2)PP织物袋的基本性质测定试验结论试验分析结果表明,PP织物袋一方面可以更好地与砂性土结合,并保证整个袋体的稳定性,另一方面,它抗拉伸和抗撕裂程度大,再加之袋体半身孔径较小,水流易通过,而土壤较大颗粒不易通过,所以PP织物袋适合作为淤地坝坝后防止渗透破坏的反滤材料。(3)坝后渗透破坏模拟试验结论1)随着渗透破坏的发生,两个模拟坝坝体内各个部位的水位高度逐渐增加到一定数值后达到稳定,即当前区域土体达到饱和,坝体内水位高度从坝前向坝后总体呈降低趋势。2)由于PP织物袋袋体孔径只容许水流和小颗粒土壤通过,因此PP织物袋装填原状土作为反滤体在防治渗透破坏时,可以减缓坝体内各个部位水位升高的速率并降低最大水位高度,使得坝体相对较难发生渗透破坏。另一方面,可以将坝体内多余水分排出,降低坝体浸润线,减缓渗透破坏的发生。3)坝体的渗透破坏过程大体可以分为:坝坡下游表层浸湿阶段、渗透破坏的发生发展阶段和渗透破坏阶段三个阶段。并且两个模拟坝的渗透破坏过程和现象相似,但是PP织物袋装填原状土作为反滤体的淤地坝渗透破坏发生的三个阶段的开始发生时间都要比原土坝晚且渗流泥沙量要比原土坝小,说明PP织物袋虽不能真正地解决发生破坏的问题,但在一定程度上可以减缓渗透破坏的发生时间和破坏规模。4)两个模拟坝的渗流量随着渗透破坏的发生均呈现线性增长的趋势,并且越往后增长的幅度越大,即先缓慢增加后显著增加,最后趋于稳定,直至坝体被完全破坏;PP织物袋作为反滤体的淤地坝要比原淤地坝的渗透破坏历时要长;原淤地坝的渗流效果远差于PP织物袋装填原状土作反滤体的淤地坝的渗流效果。(4)渗透破坏试样微观研究结论1)处于坝体浸润线以下的土样的孔隙率和孔隙平均直径都要比原土料和坝体其他部位土样大,颗粒平均直径都要比原土料和坝体其他部位土样小,而孔隙圆度和粒径圆度的变化规律不明显。处于坝体最底部的土样从坝前向坝后孔隙率依次减小,且PP织物袋作反滤体的淤地坝土样的孔隙率的增大程度不及原淤地坝。2)原筑坝土料和两个模拟坝的渗流泥沙颗粒分布区间主要为20μm-100μm,原淤地坝渗透破坏过程中通过颗粒的重新分布,土体细小颗粒和部分骨架大颗粒较易流失。而PP织物袋一方面起到了防止土体较大颗粒流失的作用,在一定程度上保证了坝体的稳定性。
[Abstract]:The silt dam is one of the important water conservation engineering measures for the comprehensive treatment of the small watershed, which can not only increase the cultivated area, improve the agricultural productivity, but also prevent the water and soil loss. In the 1970s and 1980s, because of the lack of local sand and gravel, the construction of sand and gravel in the Jingbian and Dingbian areas of northern Shaanxi had not been put into the anti-filter material, which led to the seepage and destruction of the silt dam and became a risk dam. The problem has not been well solved. It is a serious safety hazard to the local silt dam project. The seepage and destruction of the dam has become an important problem to restrict the construction of the local silt dam. In this paper, the seepage and damage phenomena and the process of the silt loam of the dam in Gaojiagou, Jingbian county, Yulin City, Shaanxi Province, are studied, and the infiltration and destruction of the original silt dam under the seepage of the original silt dam are simulated. The effect of the original soil as the filter body on the infiltration duration and the infiltration line was compared with the PP fabric bag. The micro-structure and pore characteristics of the soil sample of the dam body were studied by means of scanning electron microscope, and the grain gradation of the seepage and sediment in the process of seepage failure was analyzed by the Marvin laser granulometer, and the control effect of the PP fabric bag on the penetration failure was analyzed. It is of great practical significance to provide the theoretical basis and technical support for the risk removal and reinforcement of the silt dam that produces the seepage and destruction in the Jingding area of northern Shaanxi. The main conclusions of this paper are as follows: (1) The test and analysis results of the conventional geotechnical test for dam-building materials show that the dam-building material belongs to the medium-silty soil, and the soil sample belongs to the low-liquid limit clay. The particle size distribution of the soil is not uniform, the non-uniform coefficient CU = 6.12, CC = 0.90, the condition that the CU5 and CC = 1 to 3 cannot be met at the same time, therefore, the soil sample with bad grading and the pore between the large soil particles can be more easily adopted by the small soil particles under the action of the seepage, so that the seepage and the damage can be caused. (2) The test results of the basic properties of the PP fabric bag show that the PP fabric bag can be better combined with the sandy soil in one hand, and the stability of the whole bag body is ensured, and on the other hand, the PP fabric bag has the advantages of high tensile strength and tear resistance, and small aperture of the body of the bag body, The water flow is easy to pass, and the large particles of the soil are not easy to pass, so the PP fabric bag is suitable to be used as an anti-filtration material for preventing the seepage from being damaged after the dam of the silt dam. (3) After the dam, the seepage failure simulation test (1) increases to a certain value after the level of the water level in the two simulated dam bodies is gradually increased to a certain value with the occurrence of the seepage failure, that is, the soil body in the current region is saturated, because the pore diameter of the PP fabric bag body is only allowed to pass through the water flow and the small particle soil, the PP fabric bag is filled with the original soil as the anti-filter body, The rate of water level rise in various parts of the dam body can be reduced and the maximum water level height is reduced, so that the dam body is relatively difficult to penetrate and destroy. On the other hand, the excess water in the dam body can be discharged, the infiltration line of the dam body is reduced, and the occurrence of seepage failure is reduced. and the seepage failure process and the phenomenon of the two analog dams are similar, It is indicated that the PP fabric bag can not really solve the problem of failure, but it can slow the occurrence time and the destruction scale of the penetration failure to a certain extent. and the larger the amplitude of the later growth, that is, the increase is obviously increased after the slow increase is first, and finally is stable until the dam body is completely destroyed; the silting dam of the PP fabric bag as an anti-filter body needs to be longer than that of the original silting dam; The seepage effect of the original silt dam is far from that of the silt dam in which the PP fabric bag is filled with the original soil as an anti-filter. (4) The porosity and the average diameter of the soil sample below the infiltration line of the dam body are larger than that of the original soil and the other parts of the dam body, and the average diameter of the particles is smaller than that of the original soil and the other parts of the dam body, And the variation law of the circularity of the pore and the roundness of the particle diameter is not obvious. The porosity of the soil sample at the bottom of the dam body is reduced in sequence from the front of the dam to the rear of the dam, and the increase of the porosity of the soil sample of the silt dam of the PP fabric bag as an anti-filter body is less than that of the original silt dam. The re-distribution of the particles, the fine particles of the soil and the large particles of the part of the skeleton can be easily lost during the infiltration and destruction of the original silt dam. And the PP fabric bag plays an important role in preventing the large particle loss of the soil body, and the stability of the dam body is ensured to a certain extent.
【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】：S157.31

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