Casagrande Plastic Limit Test

Fig. 3.4.4.2 Casagrande’s Liquid Limit Apparatus
Plastic limit is the boundary condition of moisture content after which soil in plastic state changes to semi solid state. The purpose of determination of plastic limit is defined as the moisture/ water content at which soil will just begins to crumble when rolled into a thread of 3mm in diameter.
For plastic limit 15g of oven dried soil passes through IS 0.425 mm sieve and mixed distilled water thoroughly until soil mass becomes plastic enough to be easily moulded in a ball with fingers and takes its portion of ball and rolled it on a glass plate with the plam into a thread like structure. The thread should be in a uniform diameter and length till it covers around 3mm diameter. When a diameter reaches 3mm, the soil is remoulded again into ball and the same process repeated until it crumbles at 3mm diameter. The crumbled thread is kept for water content determination. Repeat the test with two more samples and take their average of three water contents.
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Fig .3.4.4.3 Plastic Limit Test
Pasticity Index is defined as the difference of liquid limit and plastic limit.

IP = WL -WP
Where, WL = Liquid limt WP = Plastic limit
IP = Plasticity index
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Fig 3.4.4.4

Compaction test is of two types; light compaction test and heavy compaction test. In light compaction test cylindrical mould of capacity 1000 c.c., internal diameter 100 m.m., effective height 127.3 m.m. Rammer for light compaction is of mass 2.6 kg,, free drop height 310 m.m. and face diameter is 50 m.m. In heavy compaction test cylindrical mould of capacity 2252 c.c., internal diameter 150 m.m., effective height 127.3 m.m. Rammer for light compaction is of mass 4.89 kg,, free drop height 450 m.m. and face diameter is 50