The surcharge loading required to be placed on the horizontal backfill of a smooth retaining vertical wall so as to completely eliminate tensile crack is
- A2c
- B2c ka
- C2c √ka
- D2c/√kaCorrect
Solution
Concept
Surcharge to remove tension zone
Formula
σa = (γz + q)Ka − 2c√Ka
Step-by-step solution
1. At the top of the wall σa = q Ka − 2c√Ka. 2. For no tension: q Ka = 2c√Ka, so q = 2c/√Ka.
Explanation
The surcharge must offset the negative active pressure from cohesion.
Shortcut
q = 2c/√Ka.
Correct answer: D) 2c/√k_a