an engineering geological characterisation of tropical clays - GBV

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A standard classification of soils by particle size (Glossop and Skempton, 1945; British Code
of Practice CP 2001; BS 1377: 1975) is given in Table (7.5), for comparison purposes. In
addition, the clay fraction has been used as an index for correlating with other engineering
properties of soils (see Chapter 10).
Application of results of particle size analysis of soils is, however, usually limited by the fact
that engineering properties are also influenced by other factors such as mineral type, structure
and geological history, and which cannot be assessed from particle size tests alone (Head,
1984).
Table 7.5. Soil classification by particle size (BS 1377: 1975).
Particle size (mm) Designation Test procedure
> 200 Boulders Measurement of
200-60 Cobbles separate pieces
60-20 Coarse gravel
20-6 Medium gravel
6-2 Fine gravel Sieve analysis
2-0,6 Coarse sand
0,6-0,2 Medium sand
0,2-0,06 Fine sand
0,06-0,02 Coarse silt Sedimentation
0,02-0,006 Medium silt Analysis
0,006-0,002 Fine silt _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
0,002 and less Clay
7.2.2 Procedure and results
Particle size distribution of soils in this study was investigated by employing both the sieving
and sedimentation methods of analysis. Sieving involved use of a series and/ or set of 10
sieves of standard aperture openings (Plate 7.5). A wet sieving procedure in accordance with
British Standard (BS 1377:1975, Test 7(A)) was adopted to facilitate washing down and
separation of fines (silt and clay) from the coarse sand and gravel sizes, and thereby determine
the proportions of coarse as well as fine material present in the soils
Plate 7.5. Set of sieves used for
grain-size analysis of soils.
Plate 7.6. Sedimentation apparatus and grain-size
analysis of finer fraction of soils.