Environmetal Soil Properties and Behaviour

Environmetal Soil Properties and Behaviour


DisciplinaControle e Remediação da Poluição dos Solos5 materiais18 seguidores
Pré-visualização50 páginas
Steady population
Growth stage Decay stage
FIguRE 2.19
Schematic diagram of the survival mode of bacteria with reproduction for the long term. 
Process A: an event reproduced at an interval. Process B: an event with reproduction overlap-
ping with decay. The solid lines represent the growth stage, and the dashed lines represent the 
decay stage.
75Nature of Soils
Group II
\u2022	 Impact of \u201cfailure to perform design functions\u201d on safety, health, 
and economic welfare of the public and environment
\u2022	 Expertise of parties\u2014owners, regulators, contractors, consultants, 
and others involved.
2.9.2 Soil Type and Mineral Analysis
2.9.2.1 Soil Type
Some of the tests conducted by experienced soil engineers and practitioners 
for determination of soil type do not classify as rigorous or quantitative 
tests. Upon first encounter with a sample of a particular soil for consider-
ation for an engineering application, the experienced practitioner uses sight 
(colour), smell, feel, and in some instances, taste. With these preliminary sight-
smell-feel-taste observations, one can deduce whether (a) the particular soil 
is granular or clayey or somewhere in between, (b) some organic material 
is present in the soil, and (c) the soil is plastic or nonplastic. Whilst these 
preliminary observations are essentially qualitative in nature, they are nev-
ertheless very useful since they provide one with an initial appraisal of the 
soil under consideration. With the basic laboratory tests for soil type, this 
initial appraisal can be tested and confirmed or denied.
The basic laboratory tests generally used to identify soil type include
\u2022	 Sieve analyses and hydrometer tests for determination of grain-size 
distribution and soil texture, and to classify soil type. The important 
point to be made here is to ensure that the grab samples used for 
these tests are representative of the soil under consideration, espe-
cially if reduction of sample size is necessary. Pulverization of aggre-
gate groups, quartering procedures, and preparation and allocation 
of samples are some of the procedures that are partly qualitative in 
nature and also sensitive to operator technique.
The top portion of the protocols shown in Figure 2.20 contains some 
of the principal elements pertaining to sieve analyses for particle-
size distribution analyses and also for separation of the grab sam-
ples into sand, silt, and clay. Sieve separation into sand, silt, and clay 
is necessary if one needs information on the types of minerals in the 
soil under consideration.
\u2022	 Consistency tests to determine liquid limit, plastic limit, shrinkage 
limit, and plasticity index. It is important to note that since sample 
preparation and operator technique are significant factors in labora-
tory testing for consistency limits, the results obtained should be 
considered as operationally defined.
76 Environmental Soil Properties and Behaviour
\u2022	 Tests to determine the physical properties such as density, water 
content, degree of (water) saturation, porosity, void ratio, and spe-
cific gravity of solids. Other tests to determine such properties as 
soil rheology, compactibility, transmissivity, and others do not clas-
sify physical properties. These will be discussed in the next few 
chapters.
2.9.2.2 Mineral Analysis
The various types of tests for mineral analysis are shown in Figure  2.20. 
There is no single method that can be considered to be fully satisfactory for 
identification of the kinds of minerals in soils. In part, this is because (a) soil 
is composed of a variety of minerals and (b) there will always be a range in 
composition of the crystal structure of clay minerals from different sources. 
Techniques for determination of a single mineral will be complicated because 
of interference between the various different minerals and the less than pure 
crystal structures of the minerals. Accordingly, several methods are required 
X-ray diffraction
(XRD)
On air-dry sample
and with C3H5(OH)3
Differential
thermal analysis
(DTA)
On air-dry sample
Transmission &
scanning electron
microscopy
(TEM & SEM)
Infra-red spectra
On pellet of dry
clay and KBr
Selective chemical
dissolution (SCD)
Other\u2026..
Test
Sample
Sieve 
For particle-size 
distribution data 
or to separate
sand, silt and
clay for mineral
analyses
Sand
Identify minerals
by light
microscope
Silt
Light
microscope
and/or XRD
Clay
Wash with MgCl2
solution and
wash to remove
excess salts
M
in
er
al 
An
aly
se
s
Consistency tests
Liquid, plastic and
shrinkage limits (LL, PL, SL)Sieve to separate
gravel and larger sizes 
Remove organic matter,
carbonates and free iron.
Disperse mechanically or
by ultrasonic vibration
FIguRE 2.20
Test techniques and procedures for initial identification of soil type, consistency, and minerals. 
For detailed information on clay mineralogy (right-hand panel), one begins with the top tech-
nique (XRD) and proceeds downward with other supplementing techniques for more clarity 
in mineral identification.
77Nature of Soils
to seek identification of the different minerals in soils, especially if quantifi-
cation of these minerals is required.
X-ray diffraction (XRD) is the most useful method of identification. This is 
especially true if the samples are treated. Glycerol (C3H5(OH)3) treatment for 
detection of montmorillonite and K-saturation and heating to collapse ver-
miculite are the most common treatment methods. A comparison of the x-ray 
diffraction spacings d obtained from the [001] planes of Mg-saturated air-
dried, Mg-saturated glycerol-solvated, K-saturated air-dried, and K-saturated 
heated at 500°C samples of montmorillonite, vermiculite, and chlorite shows:
Mg-saturated, air-dried:
Montmorillonite, vermiculite, chlorite d = 1.4\u20131.5 nm
Mg-saturated, glycerol solvated:
Montmorillonite d = 1.77\u20131.8 nm
Vermiculite, chlorite d = 1.4\u20131.5 nm
K-saturated, air-dried
Chlorite, vermiculite (with interlayer aluminium) d = 1.4\u20131.5 nm
Montmorillonite d = 1.24\u20131.28 nm
K-saturated, heated (500°C)
Chlorite d = 1.4 nm
Vermiculite (contracted), montmorillonite
(contracted) d = 0.99\u20131.01 nm
X-ray diffractograms combine with differential thermal analysis (DTA) and 
measurements of infrared absorption spectrum (IR spectra) to provide a use-
ful grouping of tools for mineral identification. Clay minerals have absorption 
bands in the infrared region of the energy spectrum in the range of molecular 
bond vibration frequencies. Many of these bonds are not specific to one mineral 
because they are due to interatomic bonds common to many minerals. However, 
this should not limit the use of information from IR spectra since other support-
ing techniques such as the use of DTA can assist in sorting mineral identification.
Clay minerals lose water or undergo phase changes that give off or require 
heat at specific temperatures. The loss of water molecules causes an endo-
thermic reaction in which heat is taken up by the sample. In contrast, an 
exothermic reaction is the result of heat given off by the sample, occurring 
because of a phase change in the structure of the mineral. The tempera-
tures at which these reactions occur are characteristic of the mineral. The 
use of differential thermal analysis as a tool utilizes these thermal change 
characteristics. In essence, DTA provides information on the temperature 
at which changes occurs in a mineral when it is heated continuously to a 
78 Environmental Soil Properties and Behaviour
high temperature. The intensity of the change is directly proportional to the 
amount of the mineral in the sample being tested.
2.9.2.3 Soil Fabric and Microstructural Features
The traditional methods for viewing soil fabric include light microscopy and 
electron microscopy.