|文中首先指出当水深很大时,考虑薄膜水附加下压力的起动流速公式计算的单颗细泥沙(粘土、粉土)的起动流速很大,甚至于远超过3m/s,这与实际资料有相当出入.此外,实际现象还表明这些粘土及细颗粒起动时常常不是单颗的,而是成团进行.由此出发,再考虑粘着力及薄膜水附压力下分析了土块成团起动的临界条件,得到了成团起动的起动流速.同时对比了成团(包括成片)起动流速与单颗的起动流速,得出了临界水深HK.当H=HK时,成团起动流速等于单颗的;当H < KK时成团起动流速大于单颗的;当H > HK时成团起动流速小于单颗的.在后一种条件下,将以成团起动为主,最后通过一些数据显示,对于粘土、粉沙,HK随团块的当量粒径D0减小、干容重减小、土块扁度加大、单颗泥沙直径减小而减小,同时在一定条件下HK可以很小,已至为零;这表明成块起动可能发生在任何水深(包括水槽试验中).
|关键词: 成团起动 细颗粒 临界水深 片状土块
|The incipient motion and velocity of aggegated fine particles
Hang Qiwei, He Mingmin
China institute of Water Resources & Hydroelectric Power Research, Beijing 100044
|Under deep water, the incipient velocity calculated from the formulae for single fine particle under cohesive force and additional pressure of film water is much larger than real one and even more than 3m/s in some cases. Besides, in the nature, sometimes, thefine sediment is aggragated as soil lump or layered soil, nut not in single particle to start moving. In this paper, the critical condition of incipient motion for the aggregated soil under cohesive force and additional pressure of film water is studied, and the incipient velocity is derived. The critical depth Hk is introduced after comparing the incipient motion of single particle with that of lump and layered soil. In the cases of H(water depth) > Hk, H=Hk, or H < Hk, the incipient velocity for single particle may be greater than, equal to or Less than that of aggregated soil, respectively. When H > Hk. the incipient soil is mainly in aggregated structure. The calculation reveals that Hi reduces with the decrease of D0. the size of soil lump, dry density and single particle size, and with the increase of lump ellipticity under certain conditions. In some cases, Hk may be very small and even zero% so that in incipient motion, the sediment will be aggregated in lump or layered soil under any water depth. The formulae for aggregated fine particles have been verified in laboratory, and show good agreement with the observed data.
|Key words: Incipient motion of lump fine particle criticle depth layered soil