黏性原状土起动流速试验研究

Experiment method of incipient motion of cohesive undisturbed soil

针对黏性原状土难以被水流起动、冲刷的特点,设计了专门的封闭矩形管道,使水流的平均流速完全满足黏性原状土起动、冲刷的要求。在水槽满足起动冲刷要求的前提下,采用粒子测速系统(PIV)对管道断面流速分布进行了测量,分析论证了管道的阻力规律,并比较了有压管道与开敞水槽试验结果。分析结果认为,在水流流速不是太大时,有压管道的阻力规律符合对数律。在通过试验取得垂线流速分布的情况下,可以利用对数流速分布公式计算摩阻流速,进而计算边界水流切应力,再根据谢才公式,可将起应力换算成相应河道的起动冲刷切应力。

Incipient velocity and scouring velocity of cohesive undisturbed soil are usually higher. In the incipient experiment, because the higher velocity is hard to attain in open flume, an appropriate method should be developed. In the light of the incipient velocity and scouring characteristics of cohesive undisturbed soil, a close rectangular pipe is designed and by which the velocity fully meet the experiment requirement of cohesive undisturbed soil incipient motion and scouring. PIV is used to measure section flow velocity distribution for analyzing the resistance law of conduit. The experiment results of pressure pipe and open flume are compared. The results show that the resistance law of pressure conduit obeys logarithmic distribution if flow velocity is not too large. By the measured vertical velocity distribution, the incipient scouring shear stress is calculated using the logarithmic formula of velocity distribution and Chezy formula.