Environmental Engineering Reference
In-Depth Information
conditions (buried valleys, terraces), and those deposited in the estuarine zone (deltas,
estuary soils).
Lacustrine deposits include those laid down in lakes and playas.
Coastal deposits include spits, barrier beaches, tidal marshes, and beach ridges.
Marine deposits include offshore soils and coastal-plain deposits.
Eolian Soils
Eolian deposits are transported by wind and occur as dunes, sand sheets, loess, and vol-
canic dust.
Glacial Soils
Soils deposited by glaciers or glacial waters can take many forms, subdivided into two
groups:
Moraines are deposited directly from the glacier as ground moraine (basal till,
ablation till, drumlins) or as end, terminal, and interlobate moraines.
●
Stratified drift is deposited by the meltwaters as fluvial formations (kames, kame
terraces, eskers, outwash, kettles) or lacustrine (freshwater or saltwater deposi-
tion).
●
Secondary Deposits
Original deposits modified
in situ
by climatic factors to produce duricrusts, permafrost,
and pedological soils are referred to as secondary deposits. The duricrusts include laterite,
ironstone (ferrocrete), caliche, and silcrete.
Some Engineering Relationships
General
The various classes and subclasses have characteristic properties which allow predictions
of the impact of a particular formation on construction. A classification of soils by origin
and mode of occurrence is given in
Table 7.1.
The depositional environment, the occur-
rence either as deposited or as subsequently modified, and the typical material associated
with the formation are included. A general distribution of soils in the United States, clas-
sified by origin, is illustrated in
Figure 7.1.
The nomenclature for Figure 7.1 is given in
Table 7.2.
Foundation Conditions
Generally favorable foundation conditions are associated with (1) medium dense or
denser soils characteristic of some stream channel deposits, coastal deposits, and glacial
moraines and stratified drift; (2) overconsolidated inactive clays of some coastal plains;
and (3) clay-granular mixtures characteristic of residual soils formed from sialic rocks.
Marginal foundation conditions may be associated with glacial lacustrine clays and soils
with a potential for collapse such as playa deposits, loess, and porous clays.
Poor foundation conditions may be associated with colluvium, which is often unstable
on slopes; granular soils deposited in a loose condition in floodplains, deltas, estuaries,
lakes, swamps, and marshes; active clays resulting from the decomposition of mafic rocks
and marine shales, or deposited as marine clays and uplifted to a coastal plain, or
deposited by ancient volcanic activity; and all organic deposits.
