Question

Discuss the effects of dropping the hammer in a NZ Standard Compaction Test from a height of LESS THAN 300 mm.
What effect does this have on the Optimum water content?
Plot a graph of energy versus hammer height from 250 mm to 400 mm in steps of 50 mm to illustrate your answer. Assume the mould, hammer mass, number of layers (3) and blows (27) are all constants.                                                                                               [10 marks]

Answer 1

If we are reducing the height of the drop of hammer then energy transferred by hammer is reduced and we required more blows to the compact specimens to achieve the same condition as we are getting in the Standard compaction test, Because when we are reducing the height of fall is less than 300 mm then energy transferred per blows is reduced and the specimen can not compact as compacting in standard compaction test.

Optimum moisture content decreases because compaction effort is reduces.

Height of fall	Volume let 1 unit	Number of layer	Number of blows	Mass of hammer m = 1 unit	Energy = mgh*number of blows *number of layer/volume
m				kg
0.25	1	3	27	1	20.25
0.3	1	3	27	1	24.3
0.35	1	3	27	1	28.35
0.4	1	3	27	1	32.4

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