Dropping Weight Method:
In dropping weight method, a known weight is dropped from a height on the bottom surface of the foundation trench and depth of the impression made on the soil is noted. Bearing capacity of the soil is then calculated as below:
R = Ultimate resistance offered by the soil.
h = Height from the trench bottom, from where weight is dropped
d = Depth of impression made by the falling weight.
A = Cross-sectional area of the falling weight coming in contact with the soil.
W = Weight of the falling weight.
Energy lost in penetration is equal to the potential energy of the falling weight.
Wh = R x d
R = Wh/d
Ultimate resistance of the soil/Unit area = R/A
If f is the factor of safety, the safe bearing capacity of the soil per unit area is equal to R / A x f
This method of evaluating the safe bearing capacity of the soil is an approximate method, and hence should be used in case of minor structures only or where the method of slowly applying load is impracticable.
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