宁夏银北灌区排水暗管土工布外包料透水与防淤堵性能

有效地阻止排水暗管被淤堵又能保持其稳定的透水性,是暗管排水应用中亟需解决的问题。为了深入理解排水暗管土工布外包料透水与防淤堵性能,该研究选取了常用的7种土工布,其中3种纺黏聚丙烯(Polypropylene,PP)无纺布,4种热熔纺黏丝无纺布,并对其中一种布进行亲水剂浸泡处理。以宁夏银北灌区土壤为例,基于室内土柱试验,依据达西定律,分析不同土工布防护措施下系统的流量衰减过程、土工布的保土能力以及防淤堵性能,并对比分析了亲水处理后土工布的反滤效果。结果表明,在排水初期,土体和土工布的渗透性下降,导致系统的排水流量持续变小,土体渗透性的变化会成为影响流量变化的主导因素,对流量衰减有75%以上的贡献度。土工布在亲水处理后,整体排流量提高了15%左右,其保土能力和防淤堵效果处理前后变化不大。针对该土质,热熔纺黏丝无纺布的反滤效果要明显好于纺黏PP无纺布。试验筛选出了适合该地区土壤特性的土工布,为相似土质地区暗管外包料的选择和处理方式提供了理论依据与技术支撑。

Permeability and anti-clogging performance of geotextile envelope material around subsurface drainage pipe in Yinbei Irrigation District in Ningxia

Abstract: Geotextiles are widely used as envelope materials in the construction of subsurface drainage systems around the world, due to the multiple product series, light weight, and convenient transportation. The complex and diverse soil quality has gradually brought out a wide variety of techniques of geotextiles for subsurface drainage pipe in the agricultural mechanization of China. However, the unreasonable choice of geotextile has resulted in severely clogged pipes of subsurface drainage in many irrigation areas, even prematurely lost the drainage function. It is highly urgent to effectively prevent the drainage pipe from being clogged, and further maintain the stable water permeability in the application of subsurface drainage. Two techniques of geotextile envelope are commonly used at present, including the ordinary spun-bond Polypropylene (PP) nonwoven and hot-melt spun-bonded nonwoven geotextiles. In this study, seven types of geotextiles were selected using two techniques, one of which was soaked with a hydrophilic agent. Taking the soil of Yinbei Irrigation Zone in Ningxia of China as an example, an indoor hydraulic permeability test was carried out to measure the flow attenuation under different geotextile protection. An evaluation was made on the soil-retaining capacity and anti-clogging performance of geotextile. The filtration property of geotextile was also compared before and after hydrophilic treatment. The research results indicated that the permeability coefficients of both soil and geotextiles decreased significantly in the early stage of drainage, resulting in a continuous decrease in the flow rate. There was a much greater decrease in the permeability coefficient, but a much lower impact on the flow rate in the geotextile, compared with the soil. The soil permeability coefficient made a great contribution to the flow change, more than 75% of flow attenuation. In general, the pore size and thickness of geotextile directly determined the soil conservation effect and anti-clogging ability. Correspondingly, large apertures and high thickness of geotextiles led to high soil loss and blockage, thereby deteriorating water permeability in the irrigation areas. Furthermore, there was a decrease in the percentage of soil particle size where 90% of the soil particles were smaller than this value, due mainly to a large number of fine particles intercepted at the junction of geotextile and soil layer in the ordinary spun-bond PP nonwoven geotextiles with relatively small pore size. The formation of dense filter cake was easily induced to result in the reduction of overall outflow in this experiment. As such, the hot-melt spun-bonded nonwoven geotextiles were produced to meet the high requirements given by the Food and Agriculture Organization of the United Nations (FAO). Better water permeability with a high d90 value of soil was achieved, as the active particles increased in the sand content of upper soil, where the larger pore size was easy for the fine particles of soil to flow in. The overall drainage flow increased by about 15% in the ordinary spun-bonded PP nonwoven geotextiles after hydrophilic treatment. Nevertheless, there were better soil retention capacity and anti-clogging performance in the hot-melt spun-bond nonwoven geotextiles before and after treatment, compared with the ordinary spun-bonded PP nonwoven geotextiles. Consequently, the experiment screened out the geotextile envelopes suitable for the soil characteristics of the target area. The finding can provide a sound theoretical basis and technical support for the selection and treatment of buried pipe materials in similar soil irrigation areas.