CREEP AND CONSOLIDATION - Introduction to Soft Soil Geotechnique: Content, Context and Application - page 81

Here, T hd is referred to as the hydrodynamic period. Equations (6.6) and (6.7)
show that the consolidation process is a function of c v t/h 2 , in which the layer
thickness h appears quadratic. Therefore, scaling has a pronounced (quadratic)
effect: the hydrodynamic period of a layer twice thicker becomes four times longer.

Determination of c v from oedometer test (Asaoka's method)
From the measured settlements observed in an oedometer test, the consolidation
coefficient c v , the (linear) compressibility and the permeability k can be

determined. Beside numerical methods, which may cover non-linear aspects,
graphical methods are often applied in practice, such as the square-root method
(Taylor), the log-time method (Casagrande), the hyperbola method (Sridharan and
Prakash), and the settlement method (Asaoka). Casagrande's empirical method
distinguishes the initial, primary and secondary phase of consolidation, Tayler's
method is based on (6.7) and is appropriate for the early phase of the consolidation
process, and Sridharan and Prakash' method covers the middle part of
consolidation. Asaoka's method is based on (6.6) and is not applicable for the early
phase of the consolidation. For details of these methods, reference is made to
standard textbooks.

0.2h 2 /c v

AB S &

t t

t S i

m

B

A

B C

C

S &

S i+1

S

(a) (b)
Figure 6.3 Asaoka's method

Asaoka's method is explained next. The settlement S is measured during
successive times. Three subsequent values are selected in an appropriate part of the
data at equal time intervals

t , providing that t > 0.2 h 2 / c v (to be checked
afterwards), and they are depicted in a special manner, shown in Fig 6.3b. By
measuring

and m from the graph, the following material parameters can be found

c v = 4 h 2 (1 - tan

2

)/( t ) (6.9a)

= m /( h (1-tan )) (6.9b)

And from (6.4) the permeability can now be determined: k = c v w .