Question

In liquid limit test, the crank of the Casagrande liquid limit device is turned at the rate of 2 r/s so that the cup is lifted and dropped until the two parts of the soil come into contact along the bottom of the groove for a distance of 10 mm. A test group G1 followed this standard practice, but another test group G2 used 1 r/s. How do the liquid limit values vary? Explain briefly.

Answer 1

Casagandre liquid limit test is based on a standard procedure. The group carrying out the test followijg standard procedure will have the liquid limit lesser than the group carrying out the test @ 1 r/s i.e. LLG1 < LLG2.

This is because of the extra time that group 2 is providing by rotating at a slower rate, for the soil particles to gain stability and hence not being able to close the groove. This implies the same soil will require more water for the groove to be closed at a slower rotation speed.