Environmental Engineering Reference
In-Depth Information
Outwash plain
Nassau Co., New York
Depth
N
ft
m
Brown c-f sand,
trace silt and
gravel, startified
- grading to
silty c-f sand
39
9
11
20
24
21
20
20
28
33
15
10
Black organic
clay with thin
layers fine
sand
LL = 52, PI = 29
Gray silty sand
40
60
20
80
Legend: N = Standard penetration test values
LL = Liquid limit (%)
P
I = Plasticity index
= Groundwater level
FIGURE 7.86
(Above) USGS quadrangle sheet (Patchogue, New York) illustrating the landform of the terminal moraine and
outwash plain on Long Island, New York (scale 1:24,000). (Courtesy of USGS.)
FIGURE 7.87
(Inset left) Log of test boring from glacial outwash.
Properties
Fluvial stratified drift tends to vary from loose to medium compact but normally provides
suitable support for moderately loaded foundations in the sandy phases. A log of a test
boring from the Long Island, New York, outwash plain is given in Figure 7.87. The for-
mation thickness at this location was about 35 ft.
“Bull's liver”
refers to the pure reddish silt characteristic of the outwash in many areas of
New Jersey. When encountered in foundation excavations below the water table, it often
“quakes” when disturbed by construction equipment and loses its supporting capacity.
When confined and undisturbed, however, it appears firm and can provide suitable sup-
port for light to moderately loaded foundations. Several methods of treatment have been
used: removal by excavation where thickness is limited; changing foundation level to stay
above the deposit and avoid disturbance; or “tightening” and strengthening the silt by
