For which of the following conditions, shear failure happens between the base of a shallow strip footing and the first soil reinforcement layer? (Take D as the distance between the first layer of reinforcement and base of the footing and B the width of footing.)
1
\(\rm \frac {D}{B}<\frac{2}{3}\)
2
\(\rm \frac {D}{B}>\frac{2}{3}\)
3
\(\rm \frac {D}{B}>\frac{1}{3}\)
4
\(\rm \frac {D}{B}>\frac{1}{2}\)