Introduction - Geotechnics of Organic Soils and Peat - page 4

Figure 1.4 Glacial till ( Source : http://en.wikipedia.org/wiki/Glacial_till).
Figure 1.5 Alluvial soil deposit in Red Rock Canyon State Park, California ( Source : http://en.
wikipedia.org/wiki/Alluvium).
have a wide range of hardness and particle sizes, resulting in soils which are often very
complex and heterogeneous (Figure 1.4).
The term drift encompasses all glacial soils, which can then be divided into three
categories: till, glaciofluvial and glaciolacustrine.
1.2.3 Alluvial soils
Alluvial soils, also known as fluvial soils or alluvium, are those soils transported to
their present position by rivers and streams. These soils are very common all over the
world, and many large engineering structures are built on them. The main reason is
that many of the world's major cities and civilizations are built close to or along rivers,
which used to be an important means of transportation in the past and remain so in
many parts of the world. Alluvium also often contains extensive ground water aquifers,
so it is important in the development of water supply wells and in geoenvironmental
engineering.
When a river or stream is flowing rapidly, the silts and clays remain in suspen-
sion and are carried downstream (Figure 1.5). Only sand, gravels and boulders will