Environmental Engineering Reference
In-Depth Information
- silt and clay particles are transported towards high-atmosphere and low-
pressure zones before being deposited due to changes in wind: fall in wind speed,
obstacle, capture by herbaceous vegetation or snow cover.
Loess deposits may cause serious concern for new and existing constructions.
Five to 20 m thick collapsible loess deposits investigated in Libya prior to dam
construction exhibited collapse settlements that were estimated to be as high as 1.5
to 2 m, based on laboratory testing [ANA 73].
Special examinations of the foundation soils had to be carried out prior to
construction. Problematic collapse settlements in agreement with the map in Figure
6.1 have been described in China, Brazil, Russia [ABE 79] and the US [HOU 88].
Abelev and Abelev [ABE 79] consider that loess deposits cover 13 million km
2
,
corresponding to around 10% of land territories.
Transport towards high atmosphere and
low pressure zones
Transport towards high atmosphere and
low pressure zones
Transport towards high atmosphere and
low pressure zones
High pressures
High pressures
High pressures
Glacial outwash plains,
deflation
Erosion by cold, violent
and dry winds
Glacial outwash plains,
deflation
Erosion by cold, violent
and dry winds
Glacial outwash plains,
deflation
Erosion by cold, violent
and dry winds
Zone of cover sands
Zone of cover sands
Zone of cover sands
Ice sheet
Ice sheet
Ice sheet
dunes
dunes
dunes
Zone of loess
Zone of loess
Zone of loess
Figure 6.2.
Scheme of Aeolian loess deposition in the proximity
of large ice-sheets [AND 97]
6.2. The loess in Northern France
Northern France is characterized by the presence of large loess deposits that are
relatively well known from a geological point of view.
Although Northern France has a rather wet climate, the geological disposition of
the loess deposits and the structure of loess profiles are such that some layers of
loess remain significantly unsaturated, even during the wet autumn and winter
periods.
