Consolidation Test - Soil Properties: Testing, Measurement, and Evaluation - page 294

durations greater than 24 h are required. The load increment
duration for these tests is usually taken at some multiple of
24 h and should be the standard duration for all load increments
of the test. The decision to use a time interval greater than 24 h
is usually based on experience with particular types of soils. If,
however, there is a question as to whether a 24-h period is ade-
quate, a record of height or change in height with time should be
made for the initial load increments in order to verify the adequacy
of a 24-h period. Load increment durations other than 24 h shall be
noted in the report. For pressure increments where time-versus-
deformation data are not required, leave the load on the specimen
for the same length of time as when time-versus-deformation
readings are taken.
(5.2) Test Method B —For each increment, record the height or
change in height, d , at time intervals of approximately 0.1, 0.25,
0.5, 1, 2, 4, 8, 15, 30 min, and 1, 2, 4, 8 and 24 h, measured from
the time of each incremental pressure application. The standard
load increment duration shall exceed the time required for com-
pletion of primary consolidation as determined by [B] of the “Cal-
culations” section or a criterion set by the requesting agency. For
each increment where it is impossible to verify the end of primary
consolidation (for example, low LIR or rapid consolidation), the
load increment duration shall be constant and exceed the time
required for primary consolidation of an increment applied after
the preconsolidation pressure and along the virgin compression
curve. Where secondary compression must be evaluated, apply
pressures for longer periods. The report shall contain the load
increment duration for each increment.
Note 6 —The suggested time intervals for recording height
or change in height are for typical soils and load increments.
It is often desirable to change the reading frequency to im-
prove interpretation of the data. More rapid consolidation will
require more frequent readings. For most soils, primary con-
solidation during the first load decrements will be complete in
less time (typically one-tenth) than would be required for a
load increment along the virgin compression curve. However,
at very low stresses the rebound time can be longer.
(6) To minimize swell during disassembly, rebound the specimen
back to the seating load (5 kPa). Once height changes have ceased
(usually overnight), dismantle quickly after releasing the final
small load on the specimen. Remove the specimen and the ring from
the consolidometer and wipe any free water from the ring and spec-
imen. Determine the mass of the specimen in the ring and subtract
the tare mass of the ring to obtain the final wet specimen mass, M Tf .
The most accurate determination of the specimen dry mass and wa-
ter content is found by drying the entire specimen at the end of the
test. If the soil sample is homogeneous and sufficient trimmings are