黄河三角洲暗管排水土工布外包滤料的试验研究

黄河三角洲地区多为近代黄河泥沙淤积形成的粉细砂土,其质地均一、结构松散,在农田排水明沟建设中边坡不稳定的问题突出。近年来该地区大力开展了暗管排水系统建设,但当地砂滤料来源不足,因此,迫切需要筛选出适合当地土壤特点的土工布外包滤料。该文在对研究区土壤特性分析的基础上,利用自制水力渗透仪,通过理论计算和渗透试验观测,研究了所选择土工布的反滤、透水以及防淤堵性能。结果发现,在满足测试条件的2种型号土工布中,Typar 3201G能够满足防淤堵与透水要求,但是有一定的淤堵风险;另一型号土工布(Typar SF20)则能较好的满足研究区暗管排水外包滤料的反滤、透水与防淤堵要求。研究结果表明,满足研究区特殊土壤类型的土工布外包滤料厚度不宜过大,土工布的开孔直径应符合选择标准。研究成果可为黄河三角洲地区暗管排水土工布外包滤料的选择提供技术支撑。

Experimental study on geotextile envelopes for subsurface drainage in the Yellow River Delta

Abstract: In recent years, subsurface drainage has been greatly advocated in the Yellow River Delta area for salinity control and land reclamation. With the very uniform textured silty sand as major soils in the Yellow River Delta, and lacking of gravel envelope material, there is an urgent need to select proper synthetic envelope for subsurface drainage construction in the area. Proper selection of envelope materials is critical for a subsurface drainage system construction. Geotextile envelope has multiple advantages, including good water conductivity, retaining soil particles from clogging the drains, low cost and convenience for mechanical construction. Thus geotextile envelope is widely used in subsurface drainage system constructions throughout the world. In China, however, very few subsurface drainage projects used geotextiles as envelope materials for various reasons. Therefore, geotextile envelope may find its wide application in many poorly drained areas, such as the Yellow River Delta in China provided that proper selection criteria are met. Based on soil particle size analysis and theoretical calculations, this paper presents an experimental study on geotextile material used for subsurface drainage envelope in the Yellow River Delta, China. A testing permeameter was built on the basis of existing literature-Materials for subsurface drainage system (IDP 60). The selection criteria have three major factors, including thickness, permeability and O90. After analyzing the soil particle size distribution and measuring the saturated hydraulic conductivity (Ks) with the falling head method, we chose two types of geotextiles as the tested samples. One of these geo-textiles (Geotextile A) has a larger O90 than that in the criterion by IDP 60, while the other one (Geotextile B) meets the criterion. With these essential information, we conducted a series of experimental studies to evaluate the performance of geotextiles in filtration, permeability and anti-clogging. After each run of experiment, we measured the mass and particle size distribution of the soils passed the geotextile, and the weight of the geotextiles before and after use. In addition, continued experiments were conducted to monitor the changes of saturated hydraulic conductivity of the geotextiles using the permeameter. The results showed that, among the final two candidate geo-textile materials, one type (Typar 3201G) satisfied the anti-clogging and the permeability requirement but exhibited the risk of siltation; the other one (Typar SF20) satisfied the requirements of filtration, permeability and anti-clogging. These results indicated that the appropriate geotextile envelope for the study area should be thin enough and the O90 of the material should meet the selection criterion. We also found that the all Ks of the geotextile systems decreased with time and became relatively stable after a certain time period. The deceases of Ks may be caused by clogging of the geotextiles or that of the soil columns itself. With an additional experiment to examine key factors for reducing hydraulic conductivity of the experimental system, we found that the clogging of soil columns was the primary factor and the geotextiles performed well in conducting drainage water. Findings from this research may provide technical support for subsurface drainage construction in the Yellow River Delta.