an engineering geological characterisation of tropical clays - GBV

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A graphical relationship between U and Tv is given in Figs. (7.10, 7.11, 7.12) where U is
plotted against Tv, log10(Tv) and √Tv, respectively (Terzaghi, 1943).
Fig. 7.11. Time factor Tv (log scale) related to Fig. 7.12. Square-root of time factor, √Tv,
degree of consolidation U% related to degree of consolidation U%
(Terzaghi, 1943). (Terzaghi, 1943).
The compression of soils under a given load is usually divided into three phases (Head, 1988),
and include initial compression, primary consolidation and secondary compression (Fig.
7.13). The initial compression takes place almost simultaneously with the application of a
load increment in a laboratory test and before commencement of drainage. It is a result of
compression of small pockets of gas within the pore spaces and partly to bedding down of
contact surfaces in the cell and load frame. A small proportion may be due to elastic
compression which is recoverable when the load is removed. The initial compression is
usually responsible for deviation of the laboratory curve from the theoretical curve near the
beginning of a loading increment.
Fig. 7.13. Log-time/settlement curve analysis Fig. 7.14. Analysis of square-root time/
method, showing phases of consolidation settlement curve (Taylor, 1942).
(Casagrande, 1936).