an engineering geological characterisation of tropical clays - GBV
an engineering geological characterisation of tropical clays - GBV
an engineering geological characterisation of tropical clays - GBV
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83<br />
Chapter 7<br />
Laboratory soils index <strong>an</strong>d <strong>engineering</strong> properties determination<br />
7.1 Moisture content <strong>an</strong>d index tests<br />
7.1.1 Introduction<br />
The perform<strong>an</strong>ce <strong>of</strong> soil index tests usually involves the measurement <strong>of</strong> moisture content <strong>of</strong><br />
soils, both in the natural state as well as under certain defined test conditions (i.e. consistency<br />
limits). Index tests serve to investigate the way in which the amount <strong>of</strong> water in soils c<strong>an</strong><br />
influence their behaviour. They also provide a useful method <strong>of</strong> classifying cohesive soils <strong>an</strong>d<br />
<strong>of</strong> assessing their <strong>engineering</strong> properties (Head, 1984).<br />
The index properties <strong>of</strong> soils investigated in this study include natural moisture content,<br />
Atterberg limits (liquid <strong>an</strong>d plastic limits, plasticity index), swelling capability (free swell)<br />
<strong>an</strong>d linear shrinkage.<br />
Natural moisture content <strong>an</strong>d Atterberg limits usually serve to describe <strong>an</strong>d provide a<br />
sufficient underst<strong>an</strong>ding <strong>of</strong> the nature <strong>of</strong> clay soils, as may be required by m<strong>an</strong>y applications<br />
in <strong>engineering</strong> practice; <strong>an</strong>d this especially when coupled with a knowledge <strong>of</strong> the <strong>geological</strong><br />
history <strong>of</strong> the soils (Atterberg, 1911; Nelson <strong>an</strong>d Miller, 1992).<br />
7.1.2 Natural moisture content<br />
Determination <strong>of</strong> natural moisture content <strong>of</strong> soils was carried out in this study by ovendrying<br />
method <strong>an</strong>d in accord<strong>an</strong>ce with British St<strong>an</strong>dard (BS 1377; 1975, Test 1(A)) <strong>an</strong>d<br />
Germ<strong>an</strong> St<strong>an</strong>dard, i.e. Deutsches Institut für Normung (DIN 18 121, Teil 1). This testing<br />
procedure specifies a st<strong>an</strong>dard drying temperature <strong>of</strong> 105-110 °C.<br />
Soil samples used for natural moisture content determination had been previously collected<br />
from the field, whereupon they were immediately well sealed in polythene bags to prevent<br />
moisture loss. The moisture content so determined also represents the moisture content <strong>of</strong><br />
natural undisturbed soil in situ.<br />
Natural moisture content, Wn, <strong>of</strong> a soil is usually expressed as a percentage <strong>of</strong> its dry mass<br />
(Head, 1984); <strong>an</strong>d is given by the equation<br />
natural moisture content = (loss <strong>of</strong> moisture/dry mass) * 100%, or<br />
Wn (%) = ((m2-m3)/(m3-m1)) * 100 (7.1)<br />
where m1 = mass <strong>of</strong> empty container<br />
m2 = mass <strong>of</strong> container + wet soil<br />
m3 = mass <strong>of</strong> container + dry soil<br />
In this study, up to three separate moisture content determinations were performed on each<br />
soil sample <strong>an</strong>d the average value calculated. Results <strong>of</strong> natural moisture content<br />
determination <strong>of</strong> soils performed in this study are presented in Table (7.2); <strong>an</strong>d are reported to<br />
the nearest whole number or 1%.
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