200gof air dried soil sample passing 425µm BS test sieve wasplaced on a flat glass plate and mixed thoroughly with distilled water usingpalette knives(ii) The sample was kept in an airtight container for about 24hours after mixing.
(iii) The sample was removed from thecontainer and remixed for at least 10 minutes. If necessary, further watershall be added so that the first cone penetration reading is approximately 15mm(iv) The remixed soil was poured into the cupwith a palatte knife, taking care not to trap air. The excess soil was struckoffed 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 soiland the dial gauge was noted.(vi) The cone was released to penetrate thesurface of the soil for a period of 5±1s. Then the secondreading of the dial gauge was taken.(vii) The difference between the initial gaugereading and the reading after 5 seconds’ penetration was taken as the conepenetration.(viii) The cone is then withdrawn and carefullycleaned.
A little more on the soil paste was added to the cup and the test wasrepeated. If the difference between the firstand second penetration readings was less than 0.5mm the average of the twopenetrations shall be recorded.
If the second penetration was more than 0.5mmand less than 1mm different from the first, a third test shall be carried out. If the overall range was then notmore than 1mm, a moisture content sample (about 10g) shall be taken from thearea penetrated by the cone and the moisture content determined. The average ofthe three penetration shall be recorded. If the overall range is more than 1mmthe soil shall be removed form the cup, remixed and the test repeated untilconsistent results were obtained.(ix) The test shall be repeated at least fourtimes using the same sample to which further increments of distilled water havebeen added. The amount of water added shall be chosen so that a range ofpenetration values approximately 15mm to 25mm was covered.
Calculations : The relationship between themoisture content and the cone penetration shall be plotted with the percentagemoisture contents as abscissae and the cone penetration as ordinates, both onlinear scales. The best straight line fitting the plotted points shall be drawnthrough them.Reporting ofresults : Themoisture content corresponding to a cone penetration of 20mm shall be taken asthe liquid limit of the soil and shall be expressed to the whole number.