IS Standards Series · Part 9 of 9
Retaining Wall Design per IS 456:2000
Cantilever retaining wall design per IS 456:2000 — earth pressure calculation by Rankine theory, stem and base slab structural design, stability checks for sliding, overturning and bearing pressure, and seismic earth pressure per IS 1893.
1. Wall Types and Design Approach
Cantilever retaining walls are the most common type for wall heights 3–8 m. They rely on the weight of backfill on the heel slab for stability. IS 456:2000 does not have a dedicated retaining wall chapter — structural design follows Cl.34 (slabs) and Cl.22–25 (beams/columns), with earth pressure from IS 1904 and Rankine/Coulomb theory.
| Wall Type | Height Range | Design Reference |
|---|
| Gravity (mass concrete) | Up to 3 m | IS 456 Cl.16 (plain concrete) |
| Cantilever (RC) | 3–8 m | IS 456:2000 (structural design) |
| Counterfort (RC) | 6–12 m | IS 456:2000 |
| Buttressed (RC) | 6–12 m | IS 456:2000 |
2. Earth Pressure by Rankine Theory
Active Earth Pressure
Typical Design Values
| Soil Type | φ (°) | γs (kN/m³) | Ka |
|---|
| Loose sand | 28 | 17 | 0.361 |
| Medium dense sand | 32 | 18 | 0.307 |
| Dense sand / gravel | 36 | 19 | 0.260 |
| Silty clay (c–φ) | 20 | 16 | 0.490 |
Surcharge Load
Uniform surcharge q on retained surface adds a uniform horizontal pressure of Ka·q throughout the wall height, giving an additional force Psurcharge = Ka·q·H acting at mid-height.
3. Stability Checks
Stability is checked under working (unfactored) loads:
Overturning Stability
Sliding Stability
Bearing Pressure
4. Stem Design
The stem acts as a vertical cantilever fixed at the base slab. The critical section is at the top of the base slab. Design load: factored horizontal earth pressure.
- Steel is on the backfill (tension) face
- Minimum stem thickness: H/12 to H/10 at base; 200–300 mm at top
- Shear check: Vu = 1.5 × Pa(per m); check τv ≤ τc
- Temperature and shrinkage steel on exposed face: 0.12% Ag
5. Base Slab Design
The base slab consists of a toe slab (in front of stem) and heel slab (behind stem). The net pressure on each section drives the structural design.
Toe Slab
- Net upward pressure = soil bearing pressure − self-weight of slab
- Acts as a cantilever from stem, with tension at the bottom face
- Critical section at face of stem
Heel Slab
- Net downward load = weight of soil over heel + slab self-weight − soil bearing pressure (usually net downward)
- Acts as a cantilever from stem, with tension at the top face (backfill side)
Base Slab Thickness
Typically Lbase/10 to Lbase/12 but ≥ 300 mm. Both shear and bending govern; shear usually controls in the toe.
6. Seismic Earth Pressure — IS 1893
IS 1893:2016 Part 5 (retaining walls) gives the Mononobe-Okabe method for seismic dynamic earth pressure increment. The dynamic active earth pressure coefficient Kae replaces Ka:
Simplified approach: For preliminary design in seismic zones III–V, add a seismic increment ΔPae = 0.375·Ah·γs·H² acting at 0.6H from the base (IS 1893 simplified provision). Ah is the design horizontal seismic coefficient.
7. Detailing Requirements
- Cover: 40 mm for earth face (Moderate exposure per IS 456 Cl.26.4)
- Main steel minimum: 0.12% Ag for Fe500; 0.15% for Fe250
- Distribution steel: 0.12% in the transverse (horizontal) direction
- Temperature steel (exposed face): 0.12% at least
- Waterstops: Required at construction joints in water-retaining retaining walls
- Drainage: Weep holes at 1.0–2.0 m c/c, 75–100 mm dia., backed by filter material — essential to prevent hydrostatic pressure buildup
- Key: A shear key at the base can increase sliding resistance without increasing base width; depth typically 0.3–0.5 m
Preliminary design only. Retaining wall design requires site-specific geotechnical investigation and review by a licensed structural/geotechnical engineer. Stability checks must satisfy local codes and site conditions.