The correct answer is C. The liquid limit of soil may increase.
The liquid limit of soil is the water content at which the soil has a consistency of a very soft paste. It is determined by the Casagrande liquid limit device, which consists of a cup with a handle and a base. The cup is filled with soil paste and then dropped from a height of 10 cm onto the base. The number of drops required for the soil to flow out of the cup is recorded. The liquid limit is then calculated as the water content of the soil paste at which 25 drops are required.
If the material of the base of the Casagrande liquid limit device is softer than the standard hard rubber, then the soil will flow more easily out of the cup. This is because the softer base will deform more easily under the impact of the falling cup. As a result, the number of drops required for the soil to flow out of the cup will be less, and the liquid limit will be higher.
However, it is important to note that the liquid limit is not a fixed value. It can vary depending on the type of soil, the method of testing, and the person conducting the test. Therefore, it is important to use a standard method of testing and to be aware of the potential sources of error when determining the liquid limit of soil.