Consolidation Test - Soil Properties: Testing, Measurement, and Evaluation - page 291

D 4318 (Chapters 7 and 8) using material from the sample as
specified in (1). Determinations of the Atterberg limits are neces-
sary for proper material classification but are not a requirement
of this test method.

(4) Particle Size Distribution —The particle size distribution shall
be determined in accordance with ASTM Method D 422 (Chapter 10)
(except the minimum sample size requirement shall be waived) on
a portion of the test specimen as obtained in (6) of the “Procedure”
section. A particle size analysis may be helpful when visual inspec-
tion indicates that the specimen contains a substantial fraction of
coarse-grained material but is not a requirement of this test
method.

The first step is to place an undisturbed soil specimen in the con-
solidometer. One porous stone is placed above the specimen, another
below it. The purpose of the porous stones is to allow water to flow
into and out of the specimen. This assembly is immersed in water. As
load is applied to the upper stone, the specimen is compressed, and
deformation is measured by a dial gage.
To begin a particular test, a specific pressure (e.g., 500 lb/ft 2 ) is ap-
plied to the specimen, and deformation dial readings with correspond-
ing time observations are made and recorded until deformation has
nearly ceased. Normally, this is done over a 24-h period. From these
data, a graph known as the time curve is prepared on semilogarithmic
graph paper, with time along the abscissa on the logarithmic scale and
dial readings along the ordinate on the arithmetic scale.
The foregoing procedure is repeated after doubling the applied pres-
sure, giving another graph of time versus deformation dial readings cor-
responding to the new pressure. The procedure is then repeated for
additional doublings of applied pressure until the final applied pressure
is in excess of the total pressure to which the compressible clay formation
is expected to be subjected when the proposed structure is built.
Through careful evaluation of each graph of time versus deforma-
tion dial readings, it is possible to determine the void ratio e and coeffi-
cient of consolidation c v that correspond to the specific applied pressure
or loading p for that graph. With these data, two additional graphs can
be prepared: one of void ratio versus logarithm of pressure ( e - log p
curve), with pressure along the abscissa on the logarithmic scale and
void ratio along the ordinate on the arithmetic scale, and another of
coefficient of consolidation versus logarithm of pressure ( c v - log p
curve), with pressure along the abscissa on the logarithmic scale and co-
efficient of consolidation along the ordinate on the arithmetic scale. The
e - log p curve is used to evaluate the magnitude of settlement, and the
c v - log p curve is used to estimate the time rate of settlement.
The primary results of a laboratory consolidation test, therefore,
are (1) e - log p curve, (2) c v - log p curve, and (3) initial void ratio e 0 of
the soil in situ .

PROCEDURE