Question 1

How is lateral earth pressure calculated for a retaining wall?

Accepted Answer

Active earth pressure Pa = 0.5 Ka γs H², using Rankine: Ka = tan²(45° – φ/2), where γs is soil unit weight, H is wall height, and φ is soil friction angle.

Question 2

What is the minimum factor of safety against overturning for a retaining wall?

Accepted Answer

ASCE and most codes specify FS_overturning ≥ 1.5 for normal loads and ≥ 1.2 for seismic conditions. Some local codes require 2.0 for permanent walls.

Question 3

What is the minimum factor of safety against sliding for a retaining wall?

Accepted Answer

FS_sliding ≥ 1.5 is required. Sliding resistance = μ × W + Pp (passive pressure), where μ ≈ 0.35–0.55 for concrete on soil.

Question 4

How is the eccentricity of the footing resultant checked?

Accepted Answer

The resultant of vertical forces must fall within the middle third of the footing (e ≤ B/6) to ensure the entire base remains in compression. If e > B/6, tensile stress develops and bearing capacity is reduced.

Question 5

What reinforcement is required in the stem of a cantilever retaining wall?

Accepted Answer

The stem acts as a vertical cantilever. The critical section for moment is at the base of the stem. Flexural reinforcement is designed for Mu = 0.5 Ka γs H³/3 per meter of wall width, with standard code minimums applied.

Step	Formula	Substitution	Result
H	H	4000	4000 mm
B	B	2800	2800 mm

Step	Formula	Substitution	Result
Ka	Ka	0.333	0.333 —
Pa	0.5·Ka·γ·H²	0.5·0.333·γ·H²	48.4 kN/m

Step	Formula	Substitution	Result
q,max	q_max	83.7	83.7 kPa	✓
q,allow	qa	200	200 kPa

Step	Formula	Substitution	Result
H	H	4000	4000 mm
B	B	2800	2800 mm

Step	Formula	Substitution	Result
Ka	Ka	0.333	0.333 —
Pa	0.5·Ka·γ·H²	0.5·0.333·γ·H²	48.4 kN/m

Retaining Wall

Retaining Wall Design

Geometry

Soil

Material

Retaining Wall Design

Given:

Earth Pressure

Overturning

Sliding

Bearing

Retaining Wall

Retaining Wall Design

Geometry

Soil

Material

Retaining Wall Design

Given:

Earth Pressure

Overturning

Sliding

Bearing