Following values were observed during Standard penetration test. What is the N value? Penetration of sampler (mm): 0-150, 150-300, 300-450 Number of blows: 6, 7, 11
- A8
- B14
- C18Correct
- D24
Solution
Concept
N value in SPT
Formula
N = blows for the last 300 mm
Step-by-step solution
1. The first 150 mm is the seating drive and is ignored. 2. N = 7 + 11 = 18.
Explanation
The first 150 mm is the seating drive and is ignored.
Why the other options are wrong
6 + 7 + 11 = 24 includes the seating drive.
Shortcut
Ignore the first 150 mm.
Common mistake
Adding all three counts.
Correct answer: C) 18