Sustainable Geoenvironmental Engineering Practice - Sustainable Practices in Geoenvironmental Engineering - page 495

the gravity (m/s 2 ) and η is the viscosity of water (Pa s). To suspend a spherical particle with
a diameter of D , the condition required is expressed by

2

D ( ρρ

η

− ) g

p w

v ≥ (13.2)

w

18

or

18η
ρρ

v

D ≤

w

(13.3)

( − ) g

p w

Thus, under a given convectional upward velocity, particles smaller than a given size
(weight) can be suspended and most of them can be transported with the convectional
water low. From Equation 13.2, the approximate v w value against D = 0.075 mm, can be
estimated to be v w = 4.4 mm/s. This can provide the approximate upward low velocity
necessary to suspend particles smaller than 0.075 mm. Field trials will allow for ine-tuning
of the low velocity requirements. In the case of particles larger than the anticipated maxi-
mum size, these will remain at the bottom. In a given water column system, convectional
low can segregate the suspended particles, as demonstrated in Figure 13.13 and smaller
suspended particles can be removed from a given water depth. The diameters of the par-
ticles in Figure 13.13 are expressed as D s < D < D g at steady state. It is noted that the speciic
gravity of particles and the viscosity of water will affect the result, as shown in Equation

D s suspended solids
are relatively small

ν w

D g suspended
solids are
relatively large

Immovable large particles

FIGURE 13.13
Concept for suspending smaller particles by forced convection low.