Engineering properties of peat and organic soils - Geotechnics of Organic Soils and Peat - page 58

Figure 3.10 Density bottle used for measuring soil G s in the laboratory ( courtesy www.jaytecglass.
co.uk).
The specific gravity of soil solids can be tested in the laboratory using the specific
gravity bottle method or the gas jar method (ASTM D854, BS1377: 1990). For most
mineral soils (sand, silt and clay), the specific gravity ranges from 2.60-2.80. For
organic soils, however, it is affected by the organic constituents, and cannot simply
be set to somewhere near that of mineral soils. Cellulose has a specific gravity of
approximately 1.58, while for lignin it is approximately 1.40. These low values reduce
the compounded specific gravity of organic soils. Figure 3.10 shows the density bottle
used for measuring soil G s in the laboratory. Table 3.6 shows the typical specific gravity
of various soils.
Table 3.7 summarizes the characteristics of some British peat.
3.12 SURFACE CHARGE PROPERTIES OF ORGANIC
SOILS AND PEAT
3.12.1 Cation exchange capacity
The cation exchange capacity (CEC) is the total amount of cations that a soil can hold
on its absorption complex and exchange under conditions of pH and shows the ability
of the soils to supply cations. For a soil, the CEC is due to electronegative colloidal
substances, such as clay minerals, organic matter and colloidal silica. In other words,
the quantity of exchangeable cations in the zone adjacent to the charge surface that can
be exchangeable for other cations is termed the CEC. The CEC of the soil is expressed