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 percentage of soil particle size where 90% of the soil particles 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.