The behavior of soil can be divided into four basic states.
1). Solid
2). Semi solid
3). Plastic
4). Liquid
Procedure
Get some soil sample passes through the No. 40 sieve. then add some water and mix with the sample and put it to the cup in the "Casagrande liquid limit apparatus". Then cut a groove using standard grooving tool. after that by using the crank in the apparatus, cup is lift and drop at a rate of 2 blows/sec.
Number of blows required to close the groove for a distance of 12.7 mm (0.5") along the bottom of the groove should record. ( during the test blow count should be 15 to 35 if not change the water content)
After that get some sample from the cup and put in to the oven to calculate the moisture content of the sample. This procedure is repeated by adding more moisture to the soil and mixing.
Liquid limit : The moisture content in percent required to close the groove along the bottom of the groove along the bottom of the groove after 25 blows is defined as the liquid limit.
Note: Before stating of this test, Cup should be clean, speed should 2 blows/sec, no air or holes in the cup, should mix the sample very well.
other than this there is a empirical equation to calculate the LL (liquid limit).
LL = Wn (N/25) ^ 0.121
Where,
N = Number of blows in the LL device to close 0.5'' length (20 < N <30)
Wn = Corresponding moisture content
Plastic limit test
Procedure
Take a small soil sample and make a small soil thread. Diameter should be 3 mm. if the thread can prepare without any cracks moisture content is higher than plastic limit. if the cracks appear while rolling that is the plastic limit. from that sample determine the moisture content. that will be the plastic limit.
Plastic Index - PI
PI = LL - PL
where,
PI = Plastic index
LL = Liquid limit
PL = Plastic limit
Liquid Index - PI
LI = (w - PL) / PI
where,
w = natural moisture content
No comments:
Post a Comment