汉南长江干堤防渗排水相结合的渗流控制措施研究

Study on the Effects of Compound Seepage Control Measures by Combining Seepage Prevention with Drainage Measure in Hannan Yangtze River Dike

汉南长江干堤某堤段管涌险情整治工程受到西气东输穿堤管线影响,全封闭防渗墙被分隔而不连续导致端部出现绕渗问题。针对防渗墙未封闭段渗流控制问题,提出防渗排水相结合的渗流控制思路,堤防主体采用全封闭防渗墙防渗,西气东输管线穿堤段采用减压井排水控制地下水头。为综合评价防渗排水相结合的渗流控制措施效果,基于MODFLOW构建了汉南长江干堤三维渗流数值模型,通过数值模拟方法对比分析了无渗控措施、仅采用全封闭防渗墙以及考虑防渗墙端部绕渗影响下防渗墙与减压井相结合的渗控措施对堤防渗流场状态及渗透稳定的影响,研究了减压井井口高程对汉南长江干堤渗流控制效果的影响。研究结果表明:天然状态下和仅采用全封闭防渗墙措施时,汉南长江干堤堤内薄弱处汛期存在渗透破坏风险,且仅采用防渗墙措施时防渗墙缺口处绕渗明显。在防渗墙未封闭段设置减压井,采用全封闭防渗墙与减压井复合措施后,堤防渗流控制效果受减压井井口高程影响显著。当井口高程逐渐降低,堤内压力水头差随之增大,减压井汇流能力增强、排水减压效果明显提升,建议在设计阶段充分考虑减压井井口高程影响。

The piping burst danger control project of Hannan Yangtze River dike is affected by the West-east Gas Transmission pipeline through the dike,making the enclosed cutoff wall separated and discontinuous.This discontinuity will cause by-pass seepage at the end of the cutoff wall.To solve the potential seepage problem at the unsealed section of the cutoff wall,this paper proposes a compound seepage control and drainage measure to reduce the excessive groundwater pressure.The proposed compound measure applies the fully enclosed cutoff wall in the dike as anti-seepage measure and installs relief wells in the section of West-east Gas Transmission pipeline to control the groundwater head.To assess the effects of compound seepage control measures,a three-dimensional seepage numerical model of the Hannan Yangtze River dike was constructed based on MODFLOW.The numerical simulation method was used to compare the seepage stability of the levee without any seepage control measures,using only fully enclosed cutoff wall and using the compound seepage control measures.Effects of the wellhead elevation of relief wells on the seepage control effect in Hannan Yangtze River dike were also investigated.Results show that in the natural state,and when only enclosed cutoff wall is constructed,there is seepage risk in the weak parts of Hannan Yangtze River dike.Moreover,the seepage around the cutoff wall gap is obvious when only enclosed cutoff wall is constructed.However,when relief wells are installed in the unenclosed section of the cutoff wall,and the combined measures of fully enclosed cut-off wall and pressure relief well are adopted,the seepage control effects are significantly affected by the wellhead elevation.When the elevation of the wellhead gradually decreases,the pressure head difference in the levee increases,the confluence capacity of relief wells is enhanced,and the drainage and decompression capacity of relief wells are also obviously improved.It is suggested that the wellhead elevation of relief wells should be carefully considered in the design stage.