GATE 2018 CE (CE1) – Question 57
A 7 m high rigid smooth retaining wall with vertical backface retains saturated clay of saturated unit weight 17.2 kN/m³ and undrained cohesion 20 kPa. The difference in active lateral forces per metre wall before and after tension cracking, to two decimals, is ______ kN/m.
Practise this question in The GATE Grind →
Show answer and explanation
Correct answer: 45 to 49 OR -49 to -45
Explanation
For undrained clay, $K_a=1$, so lateral pressure is $\gamma z-2c_u$. Tension depth is $z_0=2c_u/\gamma=40/17.2=2.3256$ m. Removing the tensile triangle changes resultant magnitude by $(1/2)(40)(2.3256)=46.51$ kN/m. Both subtraction signs are officially accepted. No unspecified water-filled-crack pressure is added.