A comparison of liquid limit value determination using the Casagrande and cone penetrometer

Depending on the moisture contents, the soil behavior is revealed as solid, semisolid, plastic and liquid states. Liquid limit is an important property of fine-grained soils and Casagrande and cone penetrometer are two different methods employed for the determination of liquid limit of the soil. In forest environment, the Casagrande method is the classic method for liquid limit determination, but cone penetrometer method was not tested yet. The result of Casagrande method is related to user experience, for this end, this study was carried out to verify the differences between the two techniques for liquid limit determination. Casagrande and cone penetrometer liquid limit tests (each test repeated 4 times) were conducted using on 2 soil samples obtain from Patum and Namkhaneh district of educational and experimental forest of the University of Tehran in northern Iran. The results show liquid limit for Patum sample was near 50 and soil classes could change by a little differences in the assessment of liquid limit and the difference between the two methods is significant, but liquid limit for Namkhaneh was not near the edge and little differences in the result could not lead to change the soil classes. Comparison of coefficient variation values between two method showed that the cone penetrometer method have higher precision than Casagrande method. Finally, it is suggested that in casagrande method, before main test, some per experiment should be performed.