Question

The wall friction of the retaining wall

• A. decreases active earth pressure but increases passive earth pressure
• B. decreases passive earth pressure but increases active earth pressure
• C. decrease both active and passive earth pressure
• D. increase both active and passive earth pressure

Answer 1

The correct option is A decreases active earth pressure but increases passive earth pressure

The anlge of friction $\left(\delta \right)$ between the soil and the wall can be determined from direct shear test. The value of $\delta$ may range from $\frac{1}{2}\varphi$ to $\frac{3}{4}\varphi$ in most cases and it can be assumed as $\frac{2}{3}\varphi$ in the absence of precise data.
The wall friction decreases active earth pressure and increases passive earth pressure.
From Coulomb's theory,
$K_p=\frac{{\sin }^2(\alpha -\varphi )}{{\sin }^2\alpha \sin (\alpha +\delta )[1-\sqrt{\frac{\sin (\varphi +\delta )\sin (\varphi +\beta )}{\sin (\varphi +\delta )\sin (\varphi +\beta )}}]}$
$K_p=\frac{{\sin }^2(\alpha +\varphi )}{{\sin }^2\alpha \sin (\alpha -\delta ){[1-\sqrt{\frac{\sin (\varphi +\delta )\sin (\varphi +\beta )}{\sin (\varphi -\delta )\sin (\varphi +\beta )}}]}^2}$