Retaining-Wall Sliding FS

FS = \frac{\sum F _{resist}}{\sum F _{drive}} = \frac{W tan δ + P _{p}}{P _{a}}

Sliding: resisting shear at the base (W tanδ or cA + W tanδ) plus any passive in front, divided by horizontal active (and surcharge) thrust. Typical min FS ≈ 1.5. Also check overturning (FS ≈ 2) and bearing.

$W$: Weight of wall + soil on heel
$δ$: Base friction angle
$P_{a}$: Active thrust

Step-by-step solved example

W=300 kN/m, δ=25°, Pa=80 kN/m, Pp=0. FS sliding?

Sliding FS = resisting shear / Pa.

1. Resist
W tanδ=300 tan25°=140 kN/m.
2. FS
FS=140/80=1.75.
$FS = 1.75$

Answer: 1.75

10 practice questions

0/10 correct

1.Typical minimum sliding FS is about

2.Overturning FS uses

3.A wider heel increases W and

4.Base δ is often taken as

5.Passive in front of the toe should be

6.If Pa doubles and W is unchanged, sliding FS

7.Bearing check uses

8.A key at the base

9.Horizontal seismic (Mononobe–Okabe) typically

10.Units: W tanδ and Pa must both be