Cone Penetrometer
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The Cone Penetrometer apparatus is an alternative method to the Casagrande Device in measuring the Liquid Limit of a soil sample (See:Atterberg Limits). It is usually considered to be a more scientific approach because it is based less upon human judgement. In this method, a sample is placed in a 55 mm diameter, 40 mm deep metal cup. A stainless steel cone weighing 80 kg (including the shaft) and having a 30° angle is positioned so that its tip just touches the sample. The cone is released for 5 seconds so that it may penetrate the soil. The liquid limit is defined as the moisture content of the soil which allows the cone to penetrate exactly 20 mm during that period of time. Because it is difficult to obtain a test with exactly 20 mm penetration, the procedure is performed multiple times with a range of moisture contents and the results are interpolated.
