Question

A rigid smooth retaining wall of height 7 m with vertical back face retains saturated clay as backfill.

The saturated unit weight and undrained cohesion of the backfill are $17.2kN/m^3$ and 20 kPa, respectively. The difference in the active lateral forces on the wall (in KN per meter length of wall up to two decimal places), before and after the occurrence of tension cracks is

• A. 46.6

Answer 1

The correct option is A 46.6
Depth of tension crack

$=\frac{2C}{\gamma \sqrt{K_a}}=\frac{2\times 20}{17.2}=2.33m$

Before the development of tension crack, it will act as shown in figure.


After the development of crack we will have

The only difference that is created when tension crack is developed is the triangle 'abc'.


$f_a=\frac{1}{2}\times 2C\sqrt{K_a}\times H$

$=\frac{1}{2}\times 2\times 20\times 1\times 2.33$

= 46.6 kN/m