箱形涵洞对河床水沙特性影响的试验研究

以漳河的穿河涵洞为对象,采用物理模型的方法,就3年一遇和50年一遇洪水工况时箱形涵洞所在河道的沿程水位、上下游各断面流速及其下游河床局部冲淤变形等问题进行了试验观测,探讨了箱形涵洞对河床水沙特性的影响。试验表明:在3年一遇和50年一遇洪水工况下,箱形涵洞对上游河床的壅水较少,最大壅水高度分别为0.57m和0.3m;涵洞上游各断面的平均流速较无涵洞时有所减小,且断面横向流速分布曲线更平坦。在迎水面出现了河中心流速较左右岸流速大的现象;在涵洞下游较远的CS8断面的平均流速分别为1.8m/s和3.7m/s,与无涵洞时相差不大;在3年一遇洪水工况下,箱形涵洞洞后能形成Fr=4.52的稳定水跃,使得箱形涵洞下游CS6断面的河床局部冲刷较少,其平均冲刷深度约为0.5m。由此可见,箱形涵洞具有较优的水力条件。

Experimental Study on the Effects of Box-shaped Culvert on the Characteristics of Water and Sediment of Riverbed

A physical model based on the background of culvert crossing the Zhang River was used to investigate the impacts of box-shaped culvert on the characteristics of water and sediment of riverbed under the conditions of once-in-three-year flood and once-in-fifty-year flood. The water levels along the river, velocities on the cross-sections in the upstream and downstream reaches of box-shaped culvert, and the local scouring in the downstream reach of box-shaped culvert were measured. The results showed that (1) under the conditions of once-in-three-year flood and once-in-fifty-year flood, there is a small amount of backwater in the upstream reach of box-shaped culvert, and the maximum heights of backwater are 0.57 m and 0.3 m, respectively; (2) the mean velocities at the cross-sections in the upstream reach of box-shaped culvert are lower than those without the culvert, and the transverse velocity distribution becomes smoother with the existence of culvert; (3) the velocity in the central of river is higher than that at the left and right river banks in the upstream face; (4) the mean velocities at the cross-section of CS8 downstream of the culvert are 1.8 m/s and 3.7m/s, respectively, which are similar to those without the culvert; and (5) under the condition of once-in-three-year flood, a stable hydraulic jump can form behind the culvert with a Froude number of 4.52, which results in low local scouring of riverbed at the cross-section of CS6 downstream of the culvert with an average scour depth of 0.5 m. The conclusions suggested that the box-shaped culvert has good hydraulic conditions.