基于渗流槽试验的吸附性外包滤料改善暗管排水脱盐效果

    Improving the desalination of subsurface drain pipe with envelope adsorption filter using seepage tank test

    • 摘要: 农田暗管排水再利用是缓解西北干旱、半干旱地区灌溉水资源短缺的有效途径,而外包滤料的结构与性状是改善暗管出流水质的关键。利用自行研制的渗流槽物理模型试验设备,将取自宁夏银北暗管排水项目区的土样,结合当地盐渍化土壤特征进行重新配置,以吸附性材料代替传统砂滤料,设置了仅敷裹土工布和外裹土工布+10 cm混合滤料两种暗管外包滤料,模拟研究冬灌淋洗盐分条件下,外包滤料结构型式对暗管排水区土壤水盐运移状况的影响及其出口水质状况。监测结果表明:淋洗试验初期,渗水逐渐浸润土壤,土壤中的盐分随水流垂直向下迁移并积聚于暗管周围,即埋深60~90 cm的土层中。淋洗中期,饱和带浸润水位自下而上逐渐上升,仅敷裹土工布的暗管,当饱和带水位超过暗管轴线位置时便开始排水,而包裹混合滤料的暗管,在饱和带水位达到暗管顶部后才开始排水。仅敷裹土工布时土壤整体的平均脱盐率比铺设混合滤料时的小11.45个百分点,两轮淋洗试验后,进入铺设混合滤料暗管水样的平均矿化度较仅敷裹土工布时的水样检测值分别降低了1.89和1.21 g/L,且其暗管排水流量亦明显增大。淋洗后期,试验系统停止供水后,受重力疏干排水滞后效应影响,当饱和带浸润水位接近暗管底部时,暗管排水逐渐衰减,土壤中的盐分多呈现以暗管为中心的凹曲线分布。研究成果可为宁夏银北灌区暗管排水再利用提供参考依据。

       

      Abstract: Drainage water can be recycled from subsurface pipe networks in farmland, in order to alleviate the shortage of irrigation water resources in the arid and semi-arid regions of Northwest China. The outsourcing filter material and structure of subsurface pipes play a key role in the effluent water quality. In this study, a self-developed seepage tank device was used to simulate and investigate the effects of different outsourcing filter material structures on soil water and salt transport, drainage water quality and flow rate, as well as saturated zone water quality and water level, under winter irrigation and leaching salt conditions. Adsorption materials were used instead of traditional sand filter materials. Two types of outer filter materials were tested, namely geotextile only and geotextile wrapped with 10 cm mixed filter materials. The soil water and salt dynamics were monitored from the start of irrigation to the end of drainage. The results showed that in the early stage of the leaching test, the water gradually infiltrated the soil, where the salt migrated vertically downward with the water flow, and then accumulated around the subsurface pipes in the soil layer at a depth of 60-90 cm. In the mid-stage of leaching, the water level of the saturation zone gradually rose from the bottom to the top. The subsurface pipe with geotextile only started draining, when the water level exceeded the axis of the pipe, whereas, the subsurface pipe wrapped with geotextile and 10 cmmixed filter materials started draining only, after the water level reached the top of the pipe. In terms of the desalination performance, the soil desalination rate of both outer filter materials decreased gradually with the increase of depth. The average desalination rate of the soil with geotextile only was 11.45 percentage points lower than that with mixed filter materials. The average mineralization level of the water samples from the subsurface pipe with the mixed filter materials was reduced by 1.89 and 1.21 g/L, respectively, after subsurface pipe drainage in Test 2-1 (the first round of leaching test of subsurface pipe wrapped with geotextile+10 cm mixed filter material) and Test 2-2 (the second round of leaching test of subsurface pipe wrapped with geotextile+10 cm mixed filter material), compared with the geotextile only. The drainage flow rate also increased significantly, with the maximum drainage flow rate of 6.27 mL/s for Test 2-1 and 2.46 mL/s for Test 2-2. In the late stage of leaching, the drainage stopped under the delayed effect of gravity drainage, when the water level of the saturation zone approached the bottom of the subsurface pipe. The salt in the soil was distributed mainly in a concave curve that centered around the subsurface pipe. The findings can provide a strong reference for the subsurface pipe drainage reuse in the Yinbei irrigation district of Ningxia. Nevertheless, the experimental process cannot consider evaporation, which is one of the main factors of soil salt accumulation. At the same time, the test environment of the seepage tank was greatly varied in the actual farmland drainage from the subsurface pipe project. Therefore, better performance can be expected for the adsorption filter material on the farmland soil.

       

    /

    返回文章
    返回