Civil Engineering Reference
In-Depth Information
Figure 26.7
Volume changes in unsaturated soils.
Figure 26.7 shows bearing pressure settlement curves for unsaturated soil (the full
line) and the same soil after it has been saturated at a small bearing pressure. These
curves can be obtained from two oedometer tests: this is known as the double oedome-
ter method. There is a critical bearing pressure at which the curves cross and wetting
collapse can occur if the bearing pressure is greater than this critical value. Once wet-
ting collapse has occurred, or for bearing pressures smaller than the critical value,
wetting and drying at constant bearing pressure causes heave and settlement due to
changes in matrix suction.
26.10 Compaction and compacted soils
Construction often involves excavation and use of soil in earthworks such as road
and rail embankments, earthfill dams and land reclamation. When it is excavated soil
comes out of the ground in lumps; you can see this happening when you dig the garden.
When it is placed it must be compacted to make a stiff and strong engineering fill. The
process is illustrated in Fig. 26.8.
Figure 26.8
Earthworks.
