Deformation characteristics of peat - Geotechnics of Organic Soils and Peat - page 101

Figure 5.4 Sketch of an oedometer ( Source : http://www.ngi.no).
Figure 5.5 Consolidation behaviour of peat ( Source : http://www.roadex.org/).
or initial compression, primary consolidation and secondary compression. A fourth
phase, 'tertiary settlement' is also mentioned by some sources (Figure 5.5).
Initial compression occurs instantaneously after the load is applied, whereas pri-
mary and secondary compression depend upon the length of time the load is applied.
The initial compression occurs mainly due to the compression of gas within the pore
spaces and also due to the elastic compression of soil grains. Primary consolidation
observed during the increase in effective vertical stress causes the dissipation of excess
pore water pressure. After this dissipation has completed, secondary compression takes
place at constant effective vertical stress.