Learn: Classical retaining-wall sliding FS
A retaining wall needs a consistent balance against sliding. This traditional overall factor of safety compares the supplied resisting total with the supplied driving total; it does not derive those totals from geometry.
What the formula is saying
Divide resisting force by driving horizontal force.
Read the symbols in plain language
- R
- Total resisting force
Total resisting force. Only compatible, available and correctly referenced resistance components belong in this total.
kN/mUse kN/m as the base unit shown here. Both totals use kN/m, on the same per-metre wall basis, so the final ratio is dimensionless. Use nonnegative resisting magnitude and a strictly positive driving magnitude.
- H
- Total horizontal driving force
Total horizontal driving force. Divide matching force or moment totals to obtain the stated global safety ratio.
kN/mUse kN/m as the base unit shown here. Both totals use kN/m, on the same per-metre wall basis, so the final ratio is dimensionless. Use nonnegative resisting magnitude and a strictly positive driving magnitude.
- FSslide
- Result to find
Classical retaining-wall sliding FS. Divide matching force or moment totals to obtain the stated global safety ratio.
ratio / no unit
Sort out the units first
Both totals use kN/m, on the same per-metre wall basis, so the final ratio is dimensionless. Use nonnegative resisting magnitude and a strictly positive driving magnitude.
Assumptions before calculating
This is an idealized study model with supplied soil parameters and loading. Ground investigation, drainage condition, groundwater, geometry and the governing design approach must be established by the responsible geotechnical design process.
Let’s solve one together
Read the given values, follow each operation, then check what the result means.
Read the supplied values as one complete study case. Find FSslide and explain the result in the stated output unit.
- R · Total resisting force
- 300 kN/m
- H · Total horizontal driving force
- 150 kN/m
Identify the justified resisting total
Only compatible, available and correctly referenced resistance components belong in this total.
(300) = 300 kN/mCompare with the driving total
Divide matching force or moment totals to obtain the stated global safety ratio.
(300) ÷ (150) = 2
Does this worked answer make sense?
A ratio of 1 means equality of the supplied resisting and driving totals, not automatic design acceptance. Doubling the driving total halves the ratio if resistance stays fixed.
A second worked example — different values
A second case uses different data. Predict which way the answer will change, then calculate it without reusing the first answer.
- R · Total resisting force
- 400 kN/m
- H · Total horizontal driving force
- 250 kN/m
Identify the justified resisting total
Only compatible, available and correctly referenced resistance components belong in this total.
(400) = 400 kN/mCompare with the driving total
Divide matching force or moment totals to obtain the stated global safety ratio.
(400) ÷ (250) = 1.6
Now try your own values
Change a value or its unit. The same method will show your calculation, step by step.
Results update only when you calculate. The lesson example above stays unchanged.
Your turn — check your understanding
Solve this separate case yourself. Use only the values below; the two worked examples use different data. Give the requested result in the selected unit.
- R · Total resisting force
- 360 kN/m
- H · Total horizontal driving force
- 180 kN/m
Find: Learn: Classical retaining-wall sliding FS
A hint, not the answer
Divide resisting force by driving horizontal force.
Both totals use kN/m, on the same per-metre wall basis, so the final ratio is dimensionless. Use nonnegative resisting magnitude and a strictly positive driving magnitude.
Show the full practice solution
Compare the steps with your work; revealing a solution does not mark the lesson complete.
Identify the justified resisting total
Only compatible, available and correctly referenced resistance components belong in this total.
(360) = 360 kN/mCompare with the driving total
Divide matching force or moment totals to obtain the stated global safety ratio.
(360) ÷ (180) = 2
Avoid the common trap
Do not reverse resistance and demand or combine factored and unfactored totals without a coherent design method. Do not rely on passive soil that may be excavated or cannot mobilize.
When this method applies — and when it does not
This is a global-factor study check, not an automatic Eurocode partial-factor verification. Base friction, adhesion, passive resistance and uplift must be included only where justified and mobilizable. Bearing, contact, settlement, structural resistance and overall stability remain separate.
For study and understanding, not approval of a real structure, site operation or design. Apply the correct standard, National Annex and professional review to actual engineering work.
One idea understood. Keep going.
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Sources & further reading
References open in a new tab and explain the underlying principles. The teaching text and examples here are SimpleFlick’s own; the source organisations have not endorsed this calculator.
Reading focus: Classical retaining-wall sliding FS. Read the relevant soil phase, seepage, earth-pressure, settlement or foundation topic. Effective stress, drainage and idealized geometry determine whether the relationship applies.
Lesson updated: · Both examples and the separate practice case are checked against an independent high-precision numerical implementation. This verifies arithmetic for the stated model, not engineering certification.