Civil Engineering Reference
In-Depth Information
Figure 8.5: Determining the strength of earth using the 'figure-of-eight' technique. (a) Construction
of the figure-of-eight mould (DIN 18952). The diameters of the circles from the largest to the
smallest are: 78 mm, 52 mm, 26 mm, 10 mm. The distance between the two smallest circles is
22.5 mm. (b) The mould, consisting of two parts, when ready for use. (c) The compressed piece of
earths is hung in a steel loop with D = 140 mm; the distance between the claws holding the clay is
75 mm. The width of the claws is the same as the depth of the piece of earth: 223 mm.
Assessing compressive strength
There is a clear connection between the binding tensile strength and the compressive
strength. DIN has a standard curve from which the compressive strength can be read as
a result of the figure-of-eight tests (see Figure 8.6).
Moisture and shrinkage
Earth that holds its shape has a moisture content of 9.5-23 per cent in its nat-
ural state. The more clay it holds, the more moisture it contains. Thoroughly
dried walls have a moisture content of 3-5 per cent. This means that earth with
