Civil Engineering Reference
In-Depth Information
Boulder clay, also referred to as glacial till, is an unstratified and irregular mixture of boulders, cobbles,
gravel, sand, silt and clay of glacial origin. In spite of its name boulder clay is not a pure clay and contains
more granular material than clay particles. Moraines are gravel and sand deposits of glacial origin. Loam
is a soft deposit consisting of a mixture of sand, silt and clay in approximately equal quantities. Fill is soil
excavated from a 'borrow' area which is used for filling hollows or for the construction of earthfill struc-
tures, such as dams or embankments. Fill will sometimes contain man-made material such as crushed
concrete or bricks from demolished buildings.
1.5 Laboratory classification of soils
Soil classification enables the engineer to assign a soil to one of a limited number of groups, based on
the material properties and characteristics of the soil. The classification groups are then used as a system
of reference for soils. Soils can be classified in the field or in the laboratory. Field techniques are usually
based upon visual recognition as described above. Laboratory techniques involve several specialised tests.
1.5.1 Drying soils
Soils can be either oven or air dried. It has become standard practice to oven dry soils at a temperature
of 105°C but it should be remembered that some soils can be damaged by such a temperature. Oven
drying is necessary for water content and particle specific gravity (see Section
1.8.3
) tests but air drying
should be used whenever possible for other soil tests that also require the test sample to be dry.
1.5.2 Determination of water content, w
The most common way of expressing the amount of water present in a soil is the water content. The water
content, also called the moisture content, is given the symbol w and is the ratio of the amount of water
to the amount of dry soil.
Weight of water
Weight of solids
W
W
Mass of water
Mass of solids
M
M
w
w
w
=
=
or
w
=
=
s
s
w is usually expressed as a percentage and should be quoted to two significant figures.
Example 1.1:
Water content determination
A sample of soil was placed in a water content tin of mass 19.52 g. The combined mass
of the soil and the tin was 48.27 g. After oven drying the soil and the tin had a mass of
42.31 g.
Determine the water content of the soil.
Solution:
M
M
48 27 42 31
42 31 19 52
.
−
−
.
5 96
22 79
.
w
w
=
=
=
=
0 262
.
=
26
%
.
.
.
s
