Environmetal Soil Properties and Behaviour

Environmetal Soil Properties and Behaviour


DisciplinaControle e Remediação da Poluição dos Solos5 materiais18 seguidores
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wind, 
water, and humans. Discounting human activities, the soils formed 
from the actions of these transport agents include
Glacial soils\u2014From transport/deposition of rock grinding and ero-
sion products. Soil formations following retreat of the glaciers 
are in the form of drifts, moraines, till, drumlins, and so forth.
Lacustrian deposits\u2014These soils are former lake sediments. The 
region where soil deposits are of considerable interest is the river 
discharge zone, that is, the zone where the river feeding the lake 
enters the lake. In a sense, this is a minor version of formation of 
deltas, which are characteristic of alluvial deposits.
Fluvial deposits\u2014These soils are the result of deposition of soil mate-
rial transported by streams and rivers. It is not uncommon for the 
modern literature to include fluvial deposits under the umbrella 
of alluvial deposit.
Alluvial deposits\u2014These refer to alluvial fans and deltas and other 
water-borne deposits not associated with fluvial deposits.
Marine soils\u2014They are the result of sediments formed from deposi-
tion of suspended material in a marine environment, that is, sed-
iment/soils obtained upon retreat of the ocean from a particular 
region. Typical kinds of soils are marine clays and silts.
Aeolian deposits\u2014Formed from wind transport. Soil materials car-
ried by wind power range from fine particulates to sands, and 
soil formations are usually found as dunes, beaches, loess, and 
drifts.
1.3.2 Soil Horizons
The concept of soil horizons, part of the consideration of soil genesis, is one 
that is frequently used by pedologists and soil scientists working in agricul-
ture. We define a soil profile as a succession of soil strata generally called 
10 Environmental Soil Properties and Behaviour
soil horizons. These horizons are basically soil layers or strata constituting a 
mature soil profile, and are distinguished on the basis of distinct differences 
in texture and physical or chemical properties between neighbouring layers. 
In many instances, there will also be colour differences between these lay-
ers. These horizons are generally labelled O, A, B, and C\u2014starting from the 
top O horizon and continuing downward to the bottom C horizon. In some 
disciplines, for example, soil science, there is also a R horizon that is also 
called a D horizon. Figure 1.2 shows the horizons and the main distinguish-
ing features. We should emphasize that these horizons are not necessarily 
clearly separated; that is, the boundaries separating A from B and B from 
C are not well defined. In fact, it would be unusual to find clear separations 
between these horizons. The more usual situation would be transition zones 
between these horizons.
The degree or level of maturity of a soil profile plays an important role 
in how well the three horizons are discerned. This is because leaching is 
a major weathering agent in producing the different properties and char-
acteristics that distinguish between the A and B horizons. In the A hori-
zon, one finds soil material that has been altered by natural processes such 
as leaching and removal of leached products and other loose material by 
water or wind. This horizon is commonly called the leaching zone. The pres-
ence of concentrations of greenhouse gases in the atmosphere together with 
A Horizon
B Horizon
C Horizon
D Horizon
Leaching
zone
Zone of
accumulation
Incomplete
weathered
parent
material
Parent
material
(bedrock)
Top layer of a horizon, which is
composed of decaying vegetation,
is called the O or Ao horizon.
is zone of leaching is typically
populated by loamy soils. 
Leaching and precipitated products from
A horizon are accumulated in this zone.
Clays constitute the typical kinds of soils
in this zone, with iron minerals being
responsible for the red-brown
colour of the clays.
In soil engineering,this is the typical
\u201csubsoil\u201d zone.
Incomplete weathering of the
source rocks (parent material)
in this zone. Typically, there
is a scarcity of organic
material in this zone. 
Unaltered source rock
(parent material)
FIguRE 1.2
Soil horizons typical of a mature soil. Immature soils (soils that have not had much exposure 
to weathering and leaching phenomena) will not show distinct layering for zone classification.
11Origin and Function of Soils
decaying vegetation on the ground surface will contribute to the acidity of 
rainwater and snow, the primary leaching agents for this horizon. Note that 
when appropriate, the organic top surface of the A horizon is referred to as 
the O horizon, to identify or take into account the thin layer of organic mate-
rial consisting of decaying vegetation, plant litter, and humus.
The B horizon is characterized by leaching products and other washed mate-
rial deposited from the A horizon. The common name for this horizon is the 
zone of accumulation. Accordingly, one would expect to find various kinds of soil 
(clay) minerals, oxides, and organic matter in this stratum. This is probably the 
most common soil zone encountered in many soil engineering projects, and is 
generally referred to as the subsoil. Below this is the C horizon, normally con-
sidered to contain soil that is unaltered by weathering subsequent to deposition 
or formation. The top layer of the C horizon will contain partially weathered 
material, and the interface layer separating this horizon from unaltered solid 
rock is called the regolith. This is also sometimes referred to as the R or D layer.
Because of the slow reaction rates associated with weathering processes, 
development of mature soil profiles and soil horizons takes hundreds to 
thousands of years. As stated previously, the important factors involved 
in this time (development) period are source material, climate, vegetation, 
topography, and time. For example, warm and wet regions allow for more 
rapid chemical weathering of parent material, especially if the leaching 
agents contain organic acids. One could obtain a lesser time requirement 
for development of a mature soil profile with significant proportions of alu-
minium and iron in the zone of accumulation. Weathering of dark-coloured 
coarse-grained and fine-grained mafic rocks containing large amounts 
of iron and magnesium will produce soil profiles that will contain dark-
coloured soils that would have high clay content. On the other hand, weath-
ering of felsic rocks such as granites containing high proportions of iron 
and silica will produce soils that contain light coloured clays with significant 
proportions of quartz sands. The evidence shows that an understanding of 
how soil profiles are developed would be useful in the construction of clas-
sification schemes for soils.
1.3.3 Classification for Engineering Purposes
It is understood that whereas a full detailing of soil properties and behavioural 
patterns determined from measurements obtained from a comprehensive 
suite of laboratory tests might provide for an ideal soil classification scheme, 
this is neither feasible nor practical. This is because the engineering use of 
soils includes a large variety of applications and situations demanding spe-
cific knowledge of different types of soil properties and behavioural charac-
teristics. The purpose of soil classification is to provide a general description 
of the soil in a terminology for classification that is understood by all con-
cerned parties. To that end, it is apparent that soil classification schemes 
should be universal: that is, a large majority of stakeholders would be able 
12 Environmental Soil Properties and Behaviour
to utilize the schemes in toto or as a starting point. With experience gained 
from associated laboratory tests, one could associate the identified soil with 
certain characteristic properties or behavioural patterns.
1.3.3.1 Particle-Size