水库防渗措施及坝后排水沟距离对周边农田地下水埋深的影响

发布时间：2018-06-04 13:13

本文选题：地下水 + 土壤　；参考：《农业工程学报》2017年11期

【摘要】：干旱区平原水库渗漏对下游农田土壤的水盐动态变化影响较大,易造成土壤的次生盐渍化和沼泽化。水库常采用"上防下排"措施来降低坝后农田地下水埋深,但排水沟参数如何选择,与坝基防渗体如何联合使用,治理效果如何等都值得深入研究。该文基于非饱和土体渗流理论,以恰拉水库周边农田为研究对象,针对"上防下排"措施进行数值模拟,分析恰拉水库采用水平铺盖、悬挂式防渗墙或无防渗措施时,坝后农田地下水埋深与坝后排水沟位置及深度的关系,并针对下游坝坡稳定及坝后积水进行分析,并通过田间试验进行验证。研究表明:在不同的渗流控制方案下,农田地下水埋深均以排水沟中轴线为对称轴呈现"漏斗形"降落趋势,排水沟前地下水埋深逐渐增大,排水沟后的地下水位有一小幅度的减小,因此,"上防下排措施"从"源头"处减小渗水进入坝后农田,增大农田地下水埋深。3种方案对比显示,不同"上防下排"渗流控制方案在遏制水库渗漏和减小坝后农田地下水的效果不同。悬挂式防渗墙和无防渗体工况不能有效减小水库的渗漏量,联合排水沟使用效果较差。22倍水头的水平铺盖在渗流控制方面优于悬挂式防渗墙和无防渗体时的工况,联合坝后排水沟及时排水后,可有效的将地下水埋深控制在2.72 m左右,大于当地的地下水临界水位2.45,有效遏制坝后土壤的盐渍化趋势。排水沟设置的位置和深度对大坝稳定存在一定影响,计算实际工况(22倍水平铺盖)时下游坝坡抗滑安全系数为1.358,大于下游坝坡最小抗滑安全系数1.242,下游坝坡处于安全状态。排水沟设置后,坝趾至沟间的积水长度是产生坝后沼泽化的主要原因。计算和实测实际情况下的积水长度为0.27 m,沼泽化面积较小。此外,计算还发现避免农田沼泽化对应的排水沟最小深度为5.18 m,实际工程中排水沟深度为6 m,可见当前的防渗形式以及排水沟至坝趾的距离及深度是合理的。库水位变动、排水沟排水的及时性对坝后地下水埋深也有较大的影响,排水沟作为辅助措施应与农田排水沟(渠)、水库防渗体以及农田灌溉制度配合使用,才能更加有效的发挥作用。
[Abstract]:The leakage of reservoir in arid plain has a great influence on the dynamic change of soil water and salt in the downstream farmland, and it is easy to cause secondary salinization and marsh of the soil. In order to reduce the groundwater depth after dam, the reservoir often adopts the measures of "upper and lower drainage", but how to select the drainage ditch parameters, how to combine with the seepage control body of dam foundation, and how to control the effect are worthy of further study. Based on the seepage theory of unsaturated soil, this paper takes the farmland around the Chara Reservoir as the research object, carries on the numerical simulation for the measure of "upper and lower drainage", and analyzes the horizontal paving, hanging impervious wall or no seepage control measures. The relationship between groundwater depth behind dam and the location and depth of drainage ditch behind dam is analyzed. The stability of downstream dam slope and water accumulation behind dam are analyzed and verified by field experiments. The results show that under different seepage control schemes, the groundwater depth of farmland presents a "funnel-shaped" descending trend with the axis of drainage ditch as the axis of symmetry, and the depth of groundwater buried before the drainage ditch increases gradually. The groundwater level after drainage ditch is reduced by a small margin. Therefore, the "upper and lower drainage measures" decrease seepage from "source" to the farmland after the dam, and increase the groundwater depth of farmland by 3. 3 schemes. The effect of different seepage control schemes is different in containing reservoir leakage and reducing farmland groundwater after dam. The working condition of suspended impervious wall and impermeable body can not effectively reduce the leakage of reservoir, and the horizontal pavement with combined drainage ditch is better than that of suspended impermeable wall and impermeable body in seepage control in the aspect of seepage control. After timely drainage, the groundwater depth can be effectively controlled at 2.72 m, which is larger than the local critical groundwater level 2.45, and the salinization trend of the soil can be effectively restrained. The location and depth of drainage ditch have a certain influence on dam stability. When the actual working condition is 22 times horizontal pavement, the slope safety factor of downstream dam slope is 1.358, which is larger than the minimum sliding safety factor of downstream dam slope 1.242, and the downstream dam slope is in a safe state. The length of water stored between the toe and the ditch is the main reason for the swamping after the dam. The calculated and measured results show that the length of water is 0.27 m, and the area of swamp is small. In addition, it is found that the minimum depth of drainage ditch to avoid farmland swamp is 5.18 m, and the depth of drainage ditch is 6 m in actual engineering. It can be seen that the current seepage prevention form and the distance and depth between drainage ditch and dam toe are reasonable. The change of reservoir water level and the timeliness of drainage also have great influence on the groundwater depth after dam. As an auxiliary measure, drainage ditch should be used in coordination with farmland drainage ditch (canal, reservoir impervious body and farmland irrigation system). In order to play a more effective role.
【作者单位】：重庆三峡学院土木工程学院;河海大学环境学院;新疆农业大学水利与土木工程学院;
【基金】：国家自然科学基金项目(51309262) 重庆市科委基础与前沿研究计划项目(cstc2015jcyj A0300、cstc2015jcyj A00022) 重庆市教委科学技术研究项目(KJ1601024) 重庆三峡学院校企合作项目(16PY03)
【分类号】：S27;TV697.32

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