Environmental Engineering Reference
In-Depth Information
FIGURE 7.85
Stratified drift exposed in borrow pit (Livingston, New Jersey).
monly filled with deposits of recent soft organic soils, and are particularly troublesome to
construction. They can be quite large, extending to 60 ft in width or more.
Pitted outwash plains
result from outwash deposition over numerous ice blocks.
Valley trains
, often extending for hundreds of miles, represent deposition down major
drainage ways. Their evidence remains as terrace deposits along the Mississippi, Missouri,
Ohio, and many other rivers of the northcentral as well as northeastern United States.
They are common also to the northern European plain.
Ice-contact depositional forms
include kames, kame terraces, and eskers.
•
Kames are mounds or hummocks composed usually of poorly sorted water-lain
materials that represent the filling of crevasses or other depressions in the ice, or
between the glacier and the sides of its trough.
•
Kame terraces are kames with an obvious flat surface of linear extent
(Figure
7.91).
They can be expected to be of loose density, since they have slumped sub-
sequent to the melting of the underlying ice.
•
Eskers are sinuous ridges of assorted and relatively stratified sand and gravel
that represent the fillings of ice channels within the glacier.
Engineering Characteristics
Gradations
The grinding action of the glacier and the relatively short transport conditions before dep-
osition cause the outwash soils to be more angular than normal fluvial materials, and the
gradation reflects the source rock. In the northeastern United States, the outwash varies
from clean sands and gravel south of the Long Island terminal moraine where the rock
source was Precambrian crystallines, to fine sands and silts in New Jersey where much of
the rock source was Triassic shales and fine-grained sandstones.
