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UPSC Civil Service Exam Questions - Engineering

Q1:

If the pressure carried by a CBR specimen at 2.5 mm penetration is 3.5 N/mm2, the CBR of the soil is

A 10%

B 35%

C 50%

D 70%

ANS:C - 50%

Here pressure given is 3.5 N/mm^2 for 2.5 mm penetration and we have to find load in kg so
pressure = load / area , p=l/a and plunger dia =50 mm so,
area = 1964mm^2,
So 3.5= P /1964 so P = 6875 N,
P = 6875/9.81 = 700 kg.

Standard value of CBR for 2.5mm penetration is 1370 kg,and for 5.mm is 2055 kg
% CBR =700/1370 = 50%.