浅析动水法在混凝土衬砌渠道应用中的局限性

The limitation analysis on seepage rate measurement of concrete lined canal by inflow-outflow tests

混凝土衬砌渠道在应用动水法时其结果往往差强人意,甚或毫无意义,明晰其误差产生原因,有利于明确动水法的实际应用。本研究以石津灌区四干三分干南四支混凝土衬砌渠道为实例,通过变水位静水法测验建立了渗漏强度函数,并以同年度流量观测资料拟合了渠道流量与水深的函数关系。基于两函数,以水量平衡原理为依据,模拟1km渠道长度时动水法的实施情况。实例分析结果表明,当流量在0.4～0.8m^3/s情况下,1km渠道上下游断面流量损失为3.615～4.130×10^(-3) m^3/s,水位落差介于2.415～3.026mm。混凝土衬砌渠道渗漏量很小,1km渠道渗漏量引起的水位下降常不足5mm。动水法中水深观测常用的水尺,在流动水中已很难保证如此高精度的观测,可见混凝土衬砌渠道的测渗工作当谨慎采用动水法。

The application of inflow-outflow tests on concrete lined canal is usually unsatisfactory or meaningless.The clarification of the causes for the errors is conducive to understanding the application of inflow-outflow tests in practice.The case study is based on the four concrete lined canals in Shijin irrigation area.The seepage rate function is established by using Dropping Head Ponding Test,and the relation function between canal flow and water depth is established based on the flow observation data of the year.According to the principle of water balance,the application of inflow-outflow tests on 1 kilometer canal is simulated.The result shows that when the flow is 0.4-0.8 m^3/s,the calculated seepage rate of upstream and downstream section of 1km canal ranged from 3.615 to 4.130 10^-3 m^3/s,and the canal water leve differnce is 2.415-3.026 mm.The seepage rate of concrete lined canal is so small that the water level drops less than 5 mm.It is difficult to measure with such high accuracy by staff gauge in flowing water.Hence,the prudent use of inflow-outflow test on concrete lined canal is proposed in the traditional measurement.