A California Bearing Ratio (CBR) test was performed on a soil subgrade and it is observed that the load value for 2.5 mm penetration is 60 kg and for 5 mm penetration is 80 kg. With the standard assumption, the CBR value of the sample is
- A3.89%
- B5.28%
- C4.37%Correct
- D6.19%
Solution
Concept
Calculation of California Bearing Ratio value
Formula
CBR = Load / Standard Load
Step-by-step solution
1. Standard load at 2.5 mm penetration is 1370 kg, and at 5.0 mm penetration is 2055 kg. 2. CBR at 2.5 mm = (60 / 1370) × 100 = 4.38% = 0.0438. 3. CBR at 5.0 mm = (80 / 2055) × 100 = 3.89% = 0.0389. Answer: C
Explanation
The standard load for 2.5 mm penetration is 1370 kg, and for 5.0 mm penetration it is 2055 kg in a California Bearing Ratio test. Dividing the test load of 60 kg by 1370 kg yields a ratio of approximately 0.0437. Since this value exceeds the ratio obtained at 5.0 mm penetration, 0.0437 is recorded as the CBR value, making option C correct.
Why the other options are wrong
NONE
Shortcut
CBR = Test Load / Standard Load (1370 kg at 2.5 mm, 2055 kg at 5 mm); adopt the higher value.
Common mistake
Selecting option A by taking the CBR value at 5 mm penetration instead of the higher governing value at 2.5 mm penetration.
Correct answer: C) 4.37%