Geoscience Reference
In-Depth Information
1982). Noteworthy is the very rapid increase in
ρ d in approximately the first 48 hours,
after which the increase was much less rapid, and the almost asymptotic approach to
the final mean bed density,
. The temporal variation of the mean dry bed density
for all three muds can be approximated by (Hayter, 1983)
ρ d
ρ d
ρ d
a ρ e pt
=
1
(11.23)
where a ρ and p are empirical coefficients.
Lane and Koelzer (1953) proposed a formula to determine the dry density of bed
material in the consolidation process, which seems to coincide with the third stage of
consolidation observed in the experiments of Nedeco (1965) and Hamm and Migniot
(1994). The Lane-Koelzer formula is
ρ
= ρ
+ β
log t
(11.24)
d
d 0
m 3 ) at time t ,
where
ρ d 0 is the dry density after 1 year of
consolidation, t is the consolidation time (years), and
ρ d is the dry density (kg
·
β
is a coefficient.
ρ d 0 and
β
depend on sediment size and reservoir operation conditions, as given in Table 11.2.
Table 11.2 ρ d 0 and β in Eq. (11.24) for dry density of reservoir deposits
(Lane and Koelzer, 1953)
Reservoir operation
Sand
Silt
Clay
ρ d 0
β d 0
β d 0
β
Sediment always submerged or
1489
0
1041
91
480
256
nearly submerged
Normally a moderate reservoir
1489
0
1185
43
737
171
drawdown
Normally considerable
1489
0
1265
16
961
96
reservoir drawdown
Reservoir normally empty
1489
0
1313
0
1249
0
Influence of consolidation on bed shear strength and erosion rate
Consolidation significantly influences the bed shear strength and, in turn, the erosion
rate. Fig. 11.10 shows the relation between dry bed density and shear strength for stat-
ically deposited beds of the Avonmouth mud observed by Owen (1975). A regression
relation between
m 2 ) and
m 3 ) can be obtained as
τ
ce (in N
·
ρ d (in kg
·
= ςρ d
τ
(11.25)
ce
10 6 and
with
ς =
6.85
×
β =
2.44.
 
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