Geotechnical Engineering

DHARM

32 GEOTECHNICAL ENGINEERING

The grain specific gravities of some common soils are listed in Table 3.1, which should
serve as a guideline to the engineer:

Table 3.1 Grain specific gravities of some soils

S. No. Soil type Grain specific gravity

1. Quartz sand 2.64 – 2.65


2. Silt 2.68 – 2.72


3. Silt with organic matter 2.40 – 2.50


4. Clay 2.44 – 2.92


5. Bentonite 2.34


6. Loess 2.65 – 2.75


7. Lime 2.70


8. Peat 1.26 – 1.80


9. Humus 1.37

The standardised detailed procedure for the determination of the specific gravity of soil
solids is contained in the Indian Standard Specification – “IS:2720 (Part-III)-1980, First Revi-
sion-Method of Test for Soils, Part III, Determination of specific gravity”. (Section 1 for fine-
grained soils and section 2 for fine, medium and coarse grained soils).

However, the general procedure is set out below:
A 50-cc density bottle or a 500-cc pycnometer may be used. While the density bottle is
the more accurate and suitable for all types of soils, the pycnometer (Fig. 3.2) is used only for
coarse-grained soils. The sequence of observations and the procedure are similar in both cases.

Hole

Brass

conical cap

Rubber

washer

Screw

ring

Glass

jar

Fig. 3.2 Pycnometer