山地河流穿越管道冲坑扩展规律的试验研究

合理预测山地河流穿越管道的未来埋深和悬空长度对其安全运营至关重要。本文以北干线输气管道穿越工程为研究对象开展了水槽模型试验,观测分析河流穿越管道附近河床演变趋势,研究流量、水深和管径等因素对冲坑扩展规律的影响。结果表明:河床演变主要由推移质泥沙输移引起,而随着管径的增大,在管底形成冲坑点的次数逐渐减少;管底形成冲刷之时冲坑竖向扩展速率很大,随着管涌的发生,冲刷速率逐渐减小,冲刷深度逐渐增大;管底冲坑竖向扩展过程满足一级动力学反应方程,归一化处理后得到了冲刷深度与冲刷时间之间关系式;水动力条件、管径和沙粒特性共同影响管底极限冲刷深度,采用Gauss-Seidel迭代法得到无量纲冲刷深度与相对泥沙粒径和弗劳德数Fr参数的关系式;当Fr>0.6时,冲坑横向扩展仅为初级扩展一个阶段,当Fr<0.6时,冲坑横向扩展过程包含初级扩展和次级扩展两阶段;最后,结合试验数据和冲坑竖向扩展经验模型,推导出冲坑横向扩展速率计算公式,且模型预测结果较好。研究结果可为探究山地河流穿越管道冲坑扩展规律及管道后期安全运营维护提供重要参考价值。

Experimental Study in Expansion Law of Scour Hole of Pipeline Crossing Mountain River

It's very important for safety of the pipeline crossing the mountain river to predict reasonably future scour depth and suspended length.A flume model test was carried out for the Beiganxian gas pipeline crossing engineering,the evolution tendency of riverbed around underwater crossing pipeline was observed and analyzed from the test,and the influencing factors of the expansion law of scour hole were studied,such as flow rates,water depths,pipe diameters and so on.The results showed that the riverbed evolution was mainly caused by bed load transport,the number of scour points formed at the bottom of the pipe decreased gradually with the increase of pipe diameter.The vertical expansion rate of the scour hole was very large when the scour was formed at the bottom of the pipe,with the occurrence of the canal gush,the scour rate decreased and the scour depth increased gradually.The vertical expansion process of the scour hole at the bottom of the pipe satisfied the first-order dynamic response equation,the relationship between scour depth and scour time was obtained after normalization.The hydraulic parameters,pipe diameters and sand characteristics all affected the scour depth of the underwater crossing pipeline.The dimensionless equation of scour depth between the relative sediment grain size and Froude number(Fr)was obtained by using the Gauss–Seidel iteration method.There was only one primary stage of horizontal expansion of the scour hole when Fr>0.6,and another following expansion process was added to the primary stage when Fr<0.6.Finally,the horizontal expansion calculation model of the scour hole was derived combined with test data and empirical model of vertical expansion,and the prediction result of the model was very good.It could provide an important reference for exploring the expansion law of the scour hole and the safe operation of the underwater crossing pipeline.