Determining the Specific Gravity of Soil - Soil Properties: Testing, Measurement, and Evaluation - page 67

Table 6-3 Expected Value for G s [2]
Type of Soil G s

Sand 2.65-2.67

Silty sand 2.67-2.70

Inorganic clay 2.70-2.80

Soils with mica or iron 2.75-3.00

Organic soils Variable, but may be under 2.00

Although the procedure for determining specific gravity of soils is
relatively simple, several warnings are in order. To begin with, all data
measurements—particularly the mass measurements—must be done
extremely accurately in order to get an accurate value of G s . It is good
practice to use the same instrument for all mass determinations in a
specific gravity test in order to eliminate any variations among instru-
ments. The accuracy of the test is also highly dependent on how well air
has been removed from the soil-and-water mixture in the pycnometer.
Both soil and water can contain air, and if not completely removed from
the soil-and-water mixture, any air entrapped inside the pycnometer
will decrease the value of M pws,t . This will, in turn, decrease the com-
puted value of the specific gravity [see Eq. (6-4)]. Finally, care must be
exercised to prevent (or at least minimize) the effects of nonuniform
temperature of the soil-and-water mixture in the pycnometer.
The specific gravity of soil is an important parameter that is used
together with other soil parameters (such as void ratio and degree of sat-
uration) to compute additional useful information. Of particular note
among the latter are the density and unit weight of soil, which are used
in many soil engineering problems.

ASTM, 2007 Annual Book of ASTM Standards , West Con-
shohocken, PA, 2007. Copyright, American Society for Testing and
Materials, 100 Barr Harbor Drive, West Conshohocken, PA 19428-
2959. Reprinted with permission.

REFERENCES

[1]

[2] Joseph E. Bowles, Engineering Properties of Soils and Their Measurement ,

2d ed., McGraw-Hill Book Company, New York, 1978.