Environmental Engineering Reference
In-Depth Information
U
E
CLAY PLUGS
GREENVILLE
LELAND
N
BRAIDED
CLAY PLUGS
CLAY
PLUGS
BACKSWAMP
HOLLANOALE
O
POINT BAR DEPOSITS
POINT BAR DEPOSITS
100
75
50
25
0
-25
-50
-75
-100
BRAIDED
BACKSWAMP
75
50
25
0
-25
-50
-75
SWALES
SWALES
SWALES
S
U
B
S
T
R
A
T
U
M
D
E
P
OS
I
T
S
ABANDONED COURSE
CLAY PLUG
T
E
R
T
I
A
R
Y
FIGURE 7.28
Deposition in a river valley in the late stage of development (pastoral zone), vicinity of Greenville, Missisippi.
(From Kolb, C. R. and Shockley, W. G.,
Proc. ASCE, J. Soil Mech. Found. Eng. Div
., July, 1289-1298, 1957. With
permission.)
Terraces result from the subsequent erosion of the bajadas as illustrated in the topo-
graphic map
(Figure 7.31).
The stratification and boulder characteristics of the higher ele-
vations of the bajada are shown in the photo of a terrace given in
Figure 7.32.
Engineering Characteristics of Fluvial Soils
General
Fluvial deposits are typically stratified and extremely variable, with frequent interbed-
ding. Permeability in the horizontal direction is significantly greater than in the vertical
direction. Unless subjected to the removal of overburden by erosion or desiccation, the
deposits are normally consolidated. Clays are soft and sands are in the loose- to medium-
dense state.
Boulders, Cobbles, and Gravel
The coarser sizes occur in the beds of youthful streams, in buried channels, and in the
upper portions of alluvial fans in arid climates. Permeability in these zones is very high.
Sands and Silts
Sands and silts are the most common fluvial deposits, occurring in all mature- and late-
stage stream valleys as valley fills, terraces, channel deposits, lag deposits, point bars, and
natural levees. They are normally consolidated and compressible unless prestressed by
overburden subsequently removed by erosion, or by water table lowering during uplift.
