Abstract:
Routine laboratory consolidation test, though simple in procedure, involves a long
time (about a week) and hence cost. Also, the determination of parameters for
estimation of settlement and rate of settlement is tedious. After involving such time
and effort, the amount of total settlement and rate of settlement estimated from test
data vary significantly from field observations. It was, therefore, envisaged that use of
the one-dimensional test with a pressure increment ratio larger than that used in
conventional tests (thereby reducing the load steps, and time) together with a suitable
mathematical model may produce the settlement information of a soil layer for a
lesser time and effort. The model will also facilitate implementation of computational
methods such as finite element method in settlement estimation. With these
objectives, a simple mathematical function is proposed that can represent the void
ratio - time relations (or dial reading - time relations) observed in a one dimensional
consolidation test .on clay soil. The model consists of three parameters. The role and
physical significance of each parameter is explained.
To verify the effectiveness of the model, consolidation tests were performed on
specimens from soil cakes reconstituted in the laboratory under two different vertical
pressures (50 kPa and 100 kPa). Tests were performed with pressure increment ratios
of 2 (used in conventional tests) and 4. The nature and amount of variation of the
model parameters were determined from these tests. Comparison of e-t, e-cr' relations
from test data and that back calculated using the model showed reasonably good
agreement testifying the effectiveness of the model.
It was observed that there is virtually no effect of using a pressure increment ratio of
4 instead 2 on the model parameters. Therefore, it is suggested that routine
consolidation tests may be performed with a larger pressure increment ratio,
especially in cases where the range of pressure to be investigated is large, together
with the model without sacrificing accuracy. The values of Cv at intermediate pressure
levels can be obtained from the model.
