Environmetal Soil Properties and Behaviour

Environmetal Soil Properties and Behaviour


DisciplinaControle e Remediação da Poluição dos Solos5 materiais18 seguidores
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initial 
grouping of soils into two major groups: coarse-grained and fine-grained 
soils\u2014and a third group (highly organic soils) that is not differentiated by 
particle-size distribution. These highly organic soils are readily identified by 
colour, odour, spongy feel, and their fibrous nature.
For the two major groups, coarse-grained soils contain more than 50% of 
soil particles greater than the number 200 sieve size, and fine-grained soils 
contain more than 50% of particles passing the number 200 sieve size. The 
following notation is used for the soils in the various groups: gravels (G), 
sands (S), fine sands and inorganic silts (M), inorganic clays (C), organic silts, 
Water Content, Percent
PlasticSemi-
solid
Liquid
Shrinkage
limit (SL)
Liquid
limit (LL)
Plastic
limit (PL)
So
il 
Vo
lu
m
e i
n 
Pr
op
or
tio
n 
to
O
ve
n-
dr
y V
ol
um
e
1.0
Total shrinkage
Solid
FIguRE 1.5
Pictorial representation of the Atterberg consistency limits. The ordinate represents the soil 
sample volume at any particular water content as a proportion of the oven-dry volume of the 
test sample.
16 Environmental Soil Properties and Behaviour
and organic clays (O). Since soils, as a rule, contain mixtures of different-
sized particles, further refinement of the two broad groups into subgroups 
can be made with (a) information on proportions of fines in the coarse-
grained group, using secondary notations of W for well graded and P for 
poorly graded and (b) the addition of Atterberg limits information for the 
fine-grained soils.
Laboratory classification criteria in the classification system use the coeffi-
cient of uniformity Cu (also called the Hazen coefficient) as an aid in grouping 
the coarse-grained soils into the W and P subgroups, where Cu = D60/D10, and 
D60 and D10 refer to grain sizes for which 60% is finer than, and for which 10% 
of the soil is finer than, respectively. For the other coarse-grained soils sub-
groups, the Atterberg limits are used in conjunction with a plasticity chart 
with the Casagrande A line (Figure 1.6). For fine-grained soils, the identifica-
tion procedures focus on the soil particle sizes less than the number 40 sieve 
size using three particular indicators: (a) dry strength, indicative of crushing 
characteristics; (b) dilatancy, indicative of reaction to shaking; and (c) tough-
ness, indicative of the consistency of the sample near the plastic limit. The 
types of soils classified under the Unified Soil Classification System are shown 
in the figure in relation to their plastic and liquid limits. Detailed descrip-
tions of the various types of soils and the Casagrande A line can be found 
in Waterways Experiment Station (1953) and Casagrande (1937), respectively.
20 40 60 80 1000
60
50
40
30
20
10 SM
and
SC M
L a
nd
 OL
MH and OH
A-l
ine
CH
Liquid Limit, Percent
Pl
as
tic
 L
im
it,
 P
er
ce
nt
CL
FIguRE 1.6
Plasticity chart used in conjunction with laboratory classification criteria in the Unified Soil 
Classification System. Detailed descriptions of the System and the Casagrande A line can be 
found in Waterways Experiment Station (1953) and Casagrande (1937), respectively.
17Origin and Function of Soils
For coarse-grained soils, the following subgroups are obtained:
\u2022	 GW for well-graded gravels, gravel\u2013sand mixtures, little or no fines
\u2022	 GP for poorly graded gravels, gravel\u2013sand mixtures, little or no fines
\u2022	 GM for silty gravels, gravel\u2013sand\u2013silt mixtures
\u2022	 GC for clayey gravels, gravel\u2013sand\u2013clay mixtures
The sands in the coarse-grained soils group are classified in the same manner:
\u2022	 SW for well-graded sands, gravelly sands, little or no fines
\u2022	 SP for poorly graded sands, gravelly sands, little or no fines
\u2022	 SM for silty sands or mixtures of sands and silts
\u2022	 SC for clayey sands or mixtures of sand and clay
The fine-grained soils (M and C) in this classification scheme are soils where 
more than 50% of the soil particles pass through the number 200 sieve size. 
For these soils, subgrouping is made on the basis of the water content at the 
liquid limit. For fine-grained soils with liquid limits less than 50%, the fol-
lowing subgroups are obtained:
\u2022	 ML for inorganic silts and very fine sands, rock flour, silty or clayey 
fine sands, or clayey silts with slight plasticity
\u2022	 CL for inorganic clays of low to medium plasticity, gravelly clays, 
sandy clays, silty clays, lean clays
\u2022	 OL for organic silts and organic silty clays of low plasticity
For fine-grained soils with liquid limits greater than 50%, the following sub-
groups are obtained:
\u2022	 MH for inorganic silts, micaceous or diatomaceous fine sandy or 
silty soils, elastic silts
\u2022	 CH for inorganic clays of high plasticity, fat clays
\u2022	 OH for organic clays of medium to high plasticity, organic silts
1.4 Basic Soil Functions
We define basic soil functions to mean the basic purposes or roles of soil in 
the ecosphere. In essence, a functioning soil is a soil that fulfils its natural 
or planned purpose, and soil functionality defines the capability of a soil 
to function in a role according to its nature, circumstance, and ecosystem 
18 Environmental Soil Properties and Behaviour
constraints. For the purposes of the discussion on basic soil functions, we 
will consider soil in the context of geoenvironment as defined by the schematic 
shown in Figure 1.7. The geoenvironment, which is a specific compartment 
of the environment, includes a significant portion of the geosphere and por-
tions of both the hydrosphere and biosphere. The earth surface material compo-
nent from the geosphere shown in the figure is defined as soil and other natural 
land surface materials (organics, debris, etc.) from the geosphere: that is, soils 
in the A, B, and C horizons and the overlying surface material. From the 
hydrosphere and the biosphere, we include the receiving waters in the land 
environment and the living or life zone in the earth. Considering only the 
soil aspects, all of these contribute to the soil ecosystem.
There are a variety of roles for soil in the geoenvironment. For convenience, 
these can be grouped into three main categories:
\u2022	 Natural in situ role of soil\u2014The role of soil is in its natural state in all 
the settings (situations) found in the geoenvironment. This includes 
residual and naturally transported soils. Soils transported in sup-
port of anthropogenic activities are not included in this group.
\u2022	 In situ role of soil with external intervention\u2014The function of soil as 
a result of human intervention.
Geoenvironment
All receiving waters on land;
includes lakes, rivers, ponds,
wetlands, estuaries,
groundwater, aquifers
Geosphere
Earth surface material 
Soil and organic surface
material overlying source
rocks (D horizon);
Soils in A, B, and C
horizons
Includes all the water
on the earth\u2019s surface
Hydrosphere
Life zone of the earth;
includes all living
organisms
Biosphere
Includes solid
continental mantle and
continental and oceanic
crust and extending
downward
Habitats and
other life zones
in the earth
surface material
FIguRE 1.7
The various constituents of the ecosphere and their relationship to the geoenvironment. Note 
that the definition of earth surface material in the left-hand column of the figure applies to all 
references to the term earth surface material.
19Origin and Function of Soils
\u2022	 Soil as a resource material\u2014This includes soil used by itself as a 
resource material, for metal recovery, and for minerals extracted 
from the soil for use as ingredients for various uses.
In turn, these main groups will spawn numerous subgroups and sub-sub-
groups. One should expect that there will be overlap between main and sub-