of air dried soil sample passing 425µm BS test sieve was
placed on a flat glass plate and mixed thoroughly with distilled water using
(ii) The sample was kept in an airtight container for about 24
hours after mixing.
The sample was removed from the
container and remixed for at least 10 minutes. If necessary, further water
shall be added so that the first cone penetration reading is approximately 15mm
(iv) The remixed soil was poured into the cup
with a palatte knife, taking care not to trap air. The excess soil was struck
offed with a straightedge to give a smooth surface.
(v) The cup of soil was placed under the cone.
Then the cone was lowered so that it touches and marks the surface of the soil
and the dial gauge was noted.
(vi) The cone was released to penetrate the
surface of the soil for a period of 5±1s. Then the second
reading of the dial gauge was taken.
(vii) The difference between the initial gauge
reading and the reading after 5 seconds’ penetration was taken as the cone
(viii) The cone is then withdrawn and carefully
cleaned. A little more on the soil paste was added to the cup and the test was
If the difference between the first
and second penetration readings was less than 0.5mm the average of the two
penetrations shall be recorded. If the second penetration was more than 0.5mm
and less than 1mm different from the first, a third test shall be carried out.
If the overall range was then not
more than 1mm, a moisture content sample (about 10g) shall be taken from the
area penetrated by the cone and the moisture content determined. The average of
the three penetration shall be recorded.
If the overall range is more than 1mm
the soil shall be removed form the cup, remixed and the test repeated until
consistent results were obtained.
(ix) The test shall be repeated at least four
times using the same sample to which further increments of distilled water have
been added. The amount of water added shall be chosen so that a range of
penetration values approximately 15mm to 25mm was covered.
The relationship between the
moisture content and the cone penetration shall be plotted with the percentage
moisture contents as abscissae and the cone penetration as ordinates, both on
linear scales. The best straight line fitting the plotted points shall be drawn
results : The
moisture content corresponding to a cone penetration of 20mm shall be taken as
the liquid limit of the soil and shall be expressed to the whole number.