A Fundamental Study on Sedimentation (Part 2) On Critical Current Velocity to Transport Particles (Continued)

Abstract

This paper mainly describes the results or experiments on "proper critical velocity" and the traction of sedimentary particles under different conditions, the theoretical relationship between proper critical velocity and settling velocity, and the geological implications of these., ("Proper critical velocity" is the mean value of velocities of currents acting at the bottom and top portions of a particle to start the movement of that particle)., Concerning the above-mentioned subject, the writer obtained the following results: (1) If the sedimentary bed has a smooth and horizontal plane, the proper critical velocity "Vp" is proportional to dn, namely, in the case of Vpr and VpII VpI=k1dnI VpII=k2d<nII> (cf., part 1), Where VpI is Vp to a single particle, VpII is Vp to the multiple particles, d is the diameter of the particle, k1·k2 and nI·nII are the constants as follows at l0°C; d<0., 14mm., ., ., k1=3700 k2=360 nI=2., 2 nII=1., 8 0., 14<d<1., 3., ., ., k1=150 k2=210 nI=1., 5 nII=1., 6 1., 3<d<6., 7 k1=35 k2=65., ., ., nI=0., 8 nII=1., 0 6., 7<d., ., ., k1=31 nI=0., 5 (2) When the particle size is fixed, Vp varies with the the density G of the particle as follows, Vp=K (G-1)β K and β are the constants, which will be given as K=1., 1 and β=O., 65, respectively, for the given size of particles, 0., 14<d<1., 3mm., However, a grain such as the fragment of a shell has a comparatively small Vp for its d and G, as it has a larger form-drag., (3) When the particle size is fixed, Vp is proportional to the roughness dr (namely the granularity of the bottom) as follows; Vp=k1dnI+(k2dnII-k1dnI) dr/d where d>dr., (4) Vp and settling velocity W are both given by the discontinuous function of d, and if d is fixed, the value of n in Vp is equal to it in W., (5) When the concentration of particles increases, Vp decreases but W increases., These results are important as factors in determining the size distribution of sediments, and its discontinuity.,