Most retaining wall failures do not come from picking a wall type that was wrong on paper. They come from water that had nowhere to go, a foundation that moved, or backfill that turned out to be clay. A wall can look fine for two dry years and start leaning in the first long wet season.
This guide explains how retaining walls work, covers 12 types with realistic height ranges, and shows how to choose between them. It also covers what most guides skip: the drainage numbers, the first signs of trouble, and the site mistakes that cause most failures.
What is a retaining wall?
A retaining wall is a structure built to hold soil, rock or fill at a different level on each side, so the ground can stand steeper than it would on its own. Left alone, soil settles to its natural angle of repose, roughly 30° to 35° for dry sand and gravel and less for wet clay. Where a site needs a sudden change in level, the wall takes the sideways push the soil would otherwise release.
That sideways push is called lateral earth pressure. It comes from the soil itself, from water in the soil, and from anything sitting on the ground above the wall.
How does a retaining wall hold back soil?
A retaining wall resists soil pressure in one of four ways: weight, structural bending, reinforced soil, or depth and anchors in the ground. Every one of the 12 types uses one of these ideas.
| How it holds soil | Types | Main idea |
|---|---|---|
| Weight | Gravity, gabion, crib, segmental block (low) | Mass of the wall plus base friction beats the push. |
| Frame and soil weight | Cantilever, counterfort, buttress | Reinforced concrete bends and uses soil on the heel as ballast. |
| Reinforced soil | MSE, segmental block with geogrid | Layers of reinforcement make the soil mass act as a wall. |
| Embedded or anchored | Sheet pile, bored pile, anchored, soil nail | Depth in the ground, tendons or nails hold the soil. |
From most calculations, the pressure on the wall grows in a straight line with depth. It is zero at the top and highest at the base, so the force is a triangle, and the total push acts at one third of the wall height above the base. The total force depends on the height squared, so a wall twice as tall carries about four times the load. Height is the biggest cost driver in any retaining wall job.
Parts of a retaining wall
Walls differ, but the parts below show up on most concrete and masonry walls. Figure 1 shows where each one sits.
| Part | What it does |
|---|---|
| Stem | The vertical wall that faces the soil. It bends like a cantilever fixed at the base slab. |
| Base slab | Spreads the load to the ground and holds the stem in place. |
| Toe | The part of the slab in front of the stem. It carries the highest ground pressure. |
| Heel | The part of the slab under the backfill. Soil on top of it adds stabilising weight. |
| Shear key | A block cast under the slab that digs into the ground and resists sliding. |
| Backfill | Soil placed behind the wall. It should be granular and free draining. |
| Drain | Gravel wrapped in filter fabric, with a perforated pipe at the bottom that leads to an outlet. |
| Weep holes | Small outlets through the stem, commonly 75 to 100 mm wide and 1.5 to 3 m apart, that let water out. |
| Surcharge | Extra load on the ground above the wall: traffic, stockpiles, a footing or a slope. |
Retaining wall vs breast wall and related structures
A retaining wall holds soil that has been filled or cut. A breast wall supports a natural hillside from the uphill side of a road. The words get mixed up often, so here is how they differ.
| Structure | What it does | Typical place |
|---|---|---|
| Retaining wall | Holds filled or cut soil where levels differ. | Roads, plots, basements, terraces |
| Breast wall | Supports a natural slope or cut face on the hill side. Built against undisturbed ground. | Hill roads |
| Boundary wall | Marks a property line. Not designed for soil pressure. | Plot edges |
| Revetment | Armours a slope against erosion. Does not hold a soil mass. | Riverbanks, coasts |
| Quay wall (bulkhead) | A retaining wall at the water's edge. | Ports, marinas |
| Basement wall | A retaining wall propped by floor slabs. | Buildings |
What are retaining walls used for?
A wall lets you use land that a natural slope would waste. A 3 m high cut at a 1 to 1.5 slope takes about 4.5 m of width. A wall holding the same cut takes well under 1 m. That difference is why walls show up wherever land is tight or expensive.
- Level building platforms on sloping and hillside plots.
- Roads and railways in cuttings and on embankments, where a slope would eat too much land.
- Bridge abutments and approach ramps, where tall fills have to end in a vertical face.
- Basements and underpasses, where the wall also carries the building.
- Erosion and flood control along rivers, canals and drainage channels.
- Slope and landslide stabilisation above or below buildings.
- Terraces, planters and driveways in landscaping.
12 types of retaining wall
The 12 types below are grouped by how they hold the soil. Each one has a labeled section, a typical height range, where it fits, where it does not, and the honest pros and cons. Height ranges are typical working ranges, not hard limits. Soil, groundwater, loads and local codes can move them either way.
1. Gravity retaining wall
A gravity retaining wall is a thick, heavy wall that resists soil pressure with its own weight. It is built from mass concrete, stone masonry, brick or large precast blocks, and usually carries little or no steel.
The weight, multiplied by the friction under the base, has to beat the sliding push. The weight acting through the base has to beat the overturning moment. Both depend on mass, so the volume of material grows roughly with the square of the height. That is why cost climbs quickly once a gravity wall passes about 3 m.
Advantages
- No reinforcement steel to corrode
- Simple to build and easy to repair
- Stone or masonry face lasts and looks good
- Forgives rough workmanship
Disadvantages
- Uses a lot of material
- Wide footprint
- Needs firm ground or it fails in bearing
- Poor value above 3 to 4 m
2. Cantilever retaining wall
A cantilever retaining wall is a reinforced concrete wall shaped like an upside-down T or an L. A vertical stem rises from a base slab and bends like a cantilever fixed at the slab.
Soil sitting on the heel presses the slab down, so stability comes from the weight of soil rather than the mass of concrete. That is why it needs far less concrete than a gravity wall of the same height. The main bars go on the soil side of the stem, because that is where the tension is.
Advantages
- Efficient use of concrete
- Design and detailing are well known
- Cast in place or precast
- Clean vertical face
Disadvantages
- Needs formwork, bar fixing and concrete control
- Excavation behind the wall for the heel
- Sliding often needs a shear key or a wider base
- Needs a base slab on decent soil
3. Counterfort retaining wall
A counterfort retaining wall is a cantilever wall with vertical triangular ribs, called counterforts, cast on the soil side between the stem and the heel slab.
The ribs tie the stem to the slab. The stem then spans sideways between ribs instead of acting as one tall cantilever, so it can stay thin. Rib spacing is commonly 2.5 to 3.5 m. Because the ribs sit behind the stem, they are in tension.
Advantages
- Thinner stem and slab at height
- Saves concrete and steel over a cantilever above about 7 m
- Better bending resistance
Disadvantages
- Complex formwork and crowded bars
- Slower to build
- Ribs sit inside the backfill, so compaction around them needs care
4. Buttress retaining wall
A buttress retaining wall has the same ribs as a counterfort wall, but they stand on the open side of the wall instead of inside the soil.
In a counterfort wall the ribs are pulled (tension). In a buttress wall they are squeezed (compression), which is the easier job for concrete. The trade-off is that the ribs take up space in front of the wall. Many guides treat the two names as one wall, but the load path and the site needs are different.
Advantages
- Ribs work in compression, which suits concrete
- Backfill is free of obstructions, so compaction is easier
- Thin stem and slab
Disadvantages
- Ribs take up usable space
- Spoils the look of the face
- Few contractors build them
5. Gabion retaining wall
A gabion retaining wall is a stack of wire-mesh baskets filled with rock and wired together. It works as a gravity wall that can bend and drain.
The wall is heavy because rock is heavy, but it is also porous and it moves without cracking. Water passes through the face, so pressure rarely builds up behind it. Rows are usually stepped back, which tilts the wall into the slope and improves stability.
Advantages
- Drains itself
- Tolerates settlement
- Quick, no cement or formwork
- Plants grow through the face
- Easy to extend
Disadvantages
- Wire corrosion sets the life of the wall
- Poor or small stone makes baskets bulge
- Wide footprint
- River gravel can wear the wire at the base
- Stone can be costly when the quarry is far away
6. Crib retaining wall
A crib wall is a gravity wall made from interlocking boxes of timber, precast concrete or steel, filled with gravel or crushed stone.
Long members parallel to the face (stretchers) and short members running into the slope (headers) form open cells. The infill supplies the weight and drains freely. The cells hold the infill in place.
Advantages
- Free draining
- Modular and quick to install
- Takes small settlements
- Plants can grow in the cells
Disadvantages
- Timber versions often last only 15 to 30 years
- Precast cribs cost more
- Wide base
- Poorly compacted infill settles
7. Mechanically stabilised earth (MSE) wall
A mechanically stabilised earth wall, also called a reinforced earth or reinforced soil wall, uses layers of geogrid, geotextile or steel strips laid in compacted fill to turn the soil itself into a gravity wall.
Friction between the fill and the reinforcement stops the soil from spreading sideways. The facing (concrete panels, blocks or wrapped geotextile) is light, because it only stops the face from ravelling. The reinforced zone is usually at least 0.7 times the wall height in length, so you need space behind the face.
Advantages
- Tolerates settlement
- Fast to build
- Cheapest per square metre of face as height rises
- Performs well in earthquakes
- No heavy foundation
Disadvantages
- Needs clean granular fill and careful compaction
- Takes a lot of land behind the face
- Utilities cannot cross the zone easily
- Needs both internal and external stability checks
8. Segmental block retaining wall
A segmental retaining wall (SRW) is built from dry-stacked, interlocking concrete blocks with no mortar. It is usually backed by a gravel drain and, for taller walls, layers of geogrid.
Blocks lock into each other with lips, pins or their shape, and each course steps back slightly. Low walls work as gravity walls. Above about 1 m, or with a driveway or slope above, the wall needs geogrid layers tied into the blocks and running back into the soil. That makes it a small MSE wall.
Advantages
- Low walls need no special skill
- Many finishes and easy curves
- Free draining
- Repair by swapping blocks
Disadvantages
- Cheap does not mean strong: missing geogrid and weak base pads cause most failures
- Needs a well-compacted base
- Joints weather and corners chip
- Not for heavy loads without design
9. Sheet pile wall
A sheet pile wall is a row of interlocking steel (sometimes vinyl, timber or precast concrete) sheets driven or pressed into the ground to hold back soil or water.
The wall works because part of it is buried. Soil in front of the buried part pushes back (passive resistance) and balances the pressure behind. A cantilever sheet pile wall works to roughly 4 or 5 m of retained height. Above that, anchors or props are added.
Advantages
- Fast installation
- No excavation behind the wall
- Holds back water
- Sheets can be pulled and reused
- Slim section
Disadvantages
- Corrodes, mostly in the splash zone
- Driving noise and vibration
- Moves a lot if not propped
- Hard to drive through obstructions
10. Bored pile wall
A bored pile wall is a line of drilled, cast-in-place concrete piles that form a wall. Contiguous piles sit side by side with small gaps. Secant piles overlap to block groundwater. Soldier piles are spaced wider, with timber or concrete lagging spanning between them.
Like sheet piles, the wall relies on embedment, but each pile is far stiffer, so it can hold back deeper cuts. A capping beam ties the pile heads together. For deeper walls, anchors or props are added.
Advantages
- Low noise and vibration compared with driving
- Stiff wall limits movement of nearby buildings
- Drills through obstructions
- Can serve as the permanent wall
Disadvantages
- High cost and slow
- Needs heavy rigs and working space
- Verticality is hard to hold on deep piles
- Contiguous walls leak through the gaps unless secant or grouted
11. Anchored (tie-back) wall
An anchored wall is a thin wall, usually sheet piles, bored piles or panels, held in place by steel tendons drilled into stable ground behind the failure wedge and grouted there.
Each tendon has a free length that passes through the soil that wants to slide, and a bonded length in stable ground beyond it. The tendon is stressed against the wall, so the wall barely moves. Because the load goes into the ground behind, the front stays clear of props.
Advantages
- Slim wall
- Clear working space in front
- Handles great heights
- Each anchor is proof-tested
- Can be re-stressed
Disadvantages
- Needs drilling plant and a skilled crew
- Capacity depends on the soil and must be tested on site
- Needs legal rights under adjacent land
- Permanent anchors need full corrosion protection
12. Soil nail wall
A soil nail wall stabilises a cut slope with closely spaced steel bars (nails) drilled and grouted into the soil, plus a thin facing of shotcrete.
Work goes from the top down. Excavate a short lift (around 1 to 2 m), drill and grout the nails, hang mesh, spray shotcrete, fit head plates, then drop to the next lift. Nails are not pre-stressed. As the soil moves a little, the nails pick up load and bind the soil into one block.
Advantages
- Fast
- Economical on cuts
- Light equipment
- Follows uneven faces
- Works where access is tight
Disadvantages
- Not for high groundwater or soft soil
- Nails reach beyond the wall line
- Needs an experienced crew and pull-out tests
- Permanent walls need corrosion protection and drainage
Retaining wall types compared side by side
Gravity, block and gabion walls suit low heights. Cantilever and MSE cover the middle range. Counterfort, MSE and anchored systems take the tallest walls. Piles, nails and anchors are the choice when you cannot dig behind the wall. Cost is relative for a typical job of that height, and local prices can change the order.
| Type | Typical height | Room behind? | Soft ground | Relative cost | Common use |
|---|---|---|---|---|---|
| Gravity | 0.5 to 3 m (1.5 to 10 ft) | Yes | Poor | Low (small walls) | Yards, rural roads |
| Cantilever | 2 to 8 m (6 to 26 ft) | Yes, for heel | Fair | Medium | Roads, plots, basements |
| Counterfort | 6 to 12 m (20 to 40 ft) | Yes | Fair | Medium to high | Tall highway walls |
| Buttress | 5 to 10 m (16 to 33 ft) | Room in front | Fair | Medium to high | Special sites |
| Gabion | 1 to 8 m (3 to 26 ft) | Yes | Good | Low to medium | Streams, slopes |
| Crib | 1 to 7 m (3 to 23 ft) | Yes | Good | Low to medium | Roadsides |
| MSE | 3 to 20 m (10 to 65 ft) | Yes, about 0.7H | Good if designed | Medium, low when tall | Highways, bridge approaches |
| Segmental block | 0.5 to 6 m (1.5 to 20 ft) | Yes | Fair | Low to medium | Residential |
| Sheet pile | 2 to 8 m (6 to 26 ft) | No | Good | Medium to high | Waterfront, temporary |
| Bored pile | 3 to 15 m (10 to 50 ft) | No | Good | High | Deep basements, urban |
| Anchored | 6 to 25 m (20 to 80 ft) | No, anchor ground | Good | High | Deep cuts |
| Soil nail | 3 to 18 m (10 to 60 ft) | No, nail ground | Poor | Low to medium | Road widening, cuts |
Retaining wall materials and lifespan
Material decides how long the wall lasts and how it fails. The ranges below are typical, and drainage and maintenance move them a lot.
| Material | Typical life | Weak point |
|---|---|---|
| Reinforced concrete | 50 to 100 years designed | Cracks let water reach the steel |
| Stone masonry | 50 years or more | Mortar joints, and no drainage behind the wall |
| Concrete blocks (dry-stacked) | Several decades | Weak base pad, missing geogrid, clogged drain |
| Gabion rock baskets | Several decades | Wire coating wearing off in salty or acidic water |
| Timber | 15 to 30 years | Rot and termites |
| Steel sheet pile | 30 to 50 years with protection | Corrosion at the water line |
How to choose the right retaining wall
Start with two questions: can you excavate behind the wall, and how tall is it? Then check the ground, the groundwater and the loads above the wall. The flow below gets you to a short list, and the table after it shows what to check.
| Factor | What to check | Where it points |
|---|---|---|
| Height | Measure from the bottom of the foundation to the top of the wall. | Up to 3 m: gravity, block, gabion. 3 to 8 m: cantilever, MSE. Taller: counterfort, MSE, anchored. |
| Room behind | Can you excavate and backfill? | Yes: open-cut walls. No: pile, nail or anchored systems. |
| Ground at base | Soft clay, loose fill, firm soil or rock. | Soft: flexible walls (gabion, MSE) or piles. Rock: almost anything. |
| Groundwater | Is the water table above the base? | High: sheet or secant piles. Avoid soil nails and unlined block. |
| Load above | Road, driveway, building or slope above the wall. | Heavy: designed cantilever or MSE. Avoid unreinforced block. |
| Access | Can a crane or drill rig reach the site? | Hand access only: block, gabion, small gravity walls. |
| Design life | Temporary or permanent? | Temporary: sheet pile, soldier pile. Permanent: concrete, MSE, protected steel. |
| Finish | Does the face need to look good? | Block, stone-faced concrete, textured panels, gabion with planted face. |
Soil matters more than most people expect. Clean sand and gravel drain well and push less on the wall. Silt and clay hold water, swell and push harder, and they make poor backfill. Soft clay under the wall is the usual reason a wall that is fine on paper tilts forward.
What forces act on a retaining wall?
The main load is lateral earth pressure, followed by water pressure and surcharge. Self-weight, earthquake, impact, wind and temperature add smaller loads that matter in special cases.
- Active earth pressure: the push when the wall moves slightly away from the soil. Most designs use this.
- At-rest pressure: higher, used for walls that cannot move, such as basement walls braced by floors.
- Passive pressure: the resistance of the soil in front of the toe or embedded part. It helps hold the wall in place.
- Water pressure: acts if water collects behind the wall. It grows with the square of the water depth.
- Surcharge: traffic, stockpiles, footings or sloping ground above the wall.
- Seismic loads: extra pressure and inertia in earthquake zones, usually found with the Mononobe-Okabe method.
- Impact: vehicle bumpers on walls that rise above a parking area or road.
For a vertical wall with level backfill, the Rankine method gives a quick estimate of the active pressure. The coefficient is Ka = (1 − sin φ) / (1 + sin φ), and the force per metre of wall is Pa = ½ × Ka × γ × H². Here φ is the soil friction angle, γ is the soil unit weight and H is the wall height. This is for checking numbers, not for final design.
Ka = (1 − 0.5) / (1 + 0.5) = 0.333
Pa = ½ × 0.333 × 18 × 4² = 48 kN per metre of wall, acting 1.33 m above the base.
Add a 10 kPa surcharge from light traffic: extra force = Ka × q × H = 0.333 × 10 × 4 = 13.3 kN/m, acting at mid-height (2 m).
Now let the backfill fill with water and give it no way out. Soil force falls to about 22 kN/m (submerged soil), but water adds ½ × 9.81 × 4² = 78.5 kN/m. Total is about 100 kN/m.
The overturning moment about the base goes from about 64 kNm/m (drained) to about 134 kNm/m (flooded). The wall did not change, but the demand more than doubled. That is the cheapest lesson in retaining wall design: drainage is structural.
Why do retaining walls fail?
Retaining walls fail in four ways: sliding, overturning, bearing failure and global slip. Structural failure of the stem or slab is a fifth, and it usually follows one of the first four or a drainage problem.
| Cause | What happens | How design avoids it |
|---|---|---|
| Water behind the wall | Pressure can double the load, and wet clay swells. | Gravel drain, filter, pipe, weep holes, surface drainage. |
| Weak foundation soil | Toe sinks, wall tilts forward. | Wider base, soil improvement, piles, or a lighter wall type. |
| Wrong backfill | Clay holds water and pushes harder. Loose fill settles. | Clean granular fill, compacted in thin layers. |
| Load nobody counted | A new driveway, shed or tree above adds pressure. | Allow for surcharge in the design and keep heavy loads back. |
| Undersized base, no key | Wall slides. | Check sliding and add a shear key or widen the base. |
| Steel on the wrong face | Stem cracks and bends. | Main bars on the soil side of a cantilever stem. |
| Slope failure underneath | Wall and soil move together. | Check global stability, especially on slopes and soft clay. |
| Scour at the toe | Stream or surface runoff undermines the base. | Embed the toe, add apron or riprap. |
Warning signs on an existing wall
A wall rarely fails without warning. Weeks or months before, it usually leans, cracks, bulges or sheds muddy water. Check for these signs after heavy rain.
| What you see | Likely cause | What to do |
|---|---|---|
| Wall leaning forward | Overturning, or soft ground under the toe | Mark it with a plumb line and a date. Call an engineer. |
| Horizontal crack near mid-height | Bending overload from water or surcharge | Check the drains and remove load behind the wall. |
| Stair-step cracks in blocks or brick | Uneven settlement | Measure the crack monthly. Look for leaks nearby. |
| Bulging face | Pressure far above design, often from water | Stop adding load. Get an engineer to look at it soon. |
| Muddy water from weep holes | Fine soil is washing out of the backfill | Filter has failed. Voids may be forming behind the wall. |
| No water from weep holes after rain | Blocked drains | Rod the holes clear and check the outlet pipe. |
| Cracks or a dip in the ground behind the wall | Wall movement or a deeper slip | Treat it as urgent. |
| Soil heaving in front of the toe | Bearing failure or global slip | Treat it as urgent. |
| White staining on the face | Water moving through concrete or mortar | Find the leak and repair the drainage. |
Do not wait if you see movement. A leaning wall with fresh cracks, a bulge, or cracks in the ground behind it can fail suddenly. Keep people and vehicles away from both sides and call a geotechnical or structural engineer.
Retaining wall drainage: what to build
A drained wall needs a gravel layer behind the stem, a filter fabric around it, a perforated pipe at the base, and a clear outlet. Weep holes alone are not a drainage system.
- Backfill with clean granular soil (gravel or coarse sand with very few fines) in thin, compacted layers.
- Place a drainage layer at least about 300 mm wide against the back of the stem.
- Wrap it in geotextile so soil fines cannot wash in and clog the gravel.
- Lay a perforated pipe (about 100 mm) at the base, falling at least 1 in 100 to an outlet or to the weep holes.
- Leave weep holes of 75 to 100 mm, commonly 1.5 to 3 m apart, and keep them above the front ground level so they do not clog.
- Seal the top of the backfill with a clay cap or paving that slopes away from the wall.
- Cut off water from uphill with a drain or ditch, and keep downspouts and irrigation away from the backfill.
Stability checks and first-sketch sizes
Engineers check a wall against sliding, overturning, bearing, eccentricity and global stability, with a minimum factor of safety on each. The usual values are below. Codes that use partial factors (such as Eurocode 7 or LRFD) express the same checks in a different format.
| Check | What it tests | Common minimum |
|---|---|---|
| Sliding | Base friction against the horizontal push | 1.5 |
| Overturning | Stabilising moment against the tipping moment about the toe | 2.0 |
| Bearing | Ground pressure under the toe against soil strength | 2.5 to 3.0 |
| Eccentricity | Where the resultant lands on the base | Inside the middle third (e ≤ B/6) |
| Global stability | Deep slip surface passing under or behind the wall | 1.3 to 1.5 |
For a first sketch of a cantilever wall of height H, these proportions are a common starting point. They come from rules of thumb, so they are for planning only. A designer has to confirm them with real soil data.
- Base width B: about 0.5H to 0.7H
- Base slab thickness: about H/10 to H/12
- Stem thickness at the bottom: about H/10 to H/12, with 200 to 300 mm at the top
- Toe length: about B/3
- Shear key: add one if sliding does not pass
Site mistakes that cause trouble
- Using clay or site spoil as backfill because it was free. It holds water, swells and pushes harder.
- Blocking the drains by paving or planting against the base, or by running weep holes into ground that cannot take the water.
- Running a heavy roller against the wall. Use a hand plate compactor near the stem. Heavy compaction there adds extra pressure.
- Backfilling too early, before the concrete has reached the strength the engineer specified.
- Ignoring surcharge. A new driveway, a parked truck, a shed or a stockpile above the wall adds load that was never in the design.
- Building on unprepared ground, such as topsoil, loose fill or a wet trench bottom, with no levelling pad.
- Putting the steel on the wrong face. In a cantilever stem the main bars go on the soil side, where the tension is.
- Leaving out joints. Long concrete walls need contraction and expansion joints, or they crack where they want to.
- Discharging roof or yard water behind the wall.
Advantages and disadvantages of retaining walls
Advantages
- Turn a steep slope into usable flat land
- Save land compared with a sloped cut or fill
- Control erosion and protect buildings, roads and channels
- Many types and materials, so there is a fit for most sites
- Long life with low maintenance when drained properly
- Can improve the look of a site with stone, block or planting
Disadvantages
- Cost rises quickly with height
- Need good design when tall or loaded
- Water pressure can wreck a poorly drained wall
- Foundation problems show up as tilt or settlement
- Need excavation, and sometimes access on neighbouring land
- Failure can be sudden and costly
Most of the disadvantages can be reduced by choices made early.
| Disadvantage | How to reduce it |
|---|---|
| Costs a lot per metre as height grows | Choose the type for the height. Cut the wall height with a gentler slope or terraces. |
| Cracks from shrinkage and temperature | Add contraction and expansion joints at the spacing the designer sets (often 6 to 10 m). |
| Water pressure behind the wall | Build the drain. Do not rely on weep holes alone. |
| Needs excavation and room behind | Pick a pile, nail or anchored system for tight sites. |
| Timber rots and attracts termites | Use treated timber, or switch to concrete or gabion. |
| Failure can be sudden and costly | Use an engineer for anything tall, loaded or above a building, and inspect each year. |
Permits and design codes
Rules differ by country, state and city. Many places ask for a permit and engineered drawings once a wall passes about 1 to 1.2 m (3 to 4 ft) in height, or when there is a slope, road, driveway or building above it. Check with the local building authority before you build. Common reference standards include:
- IS 14458 (India): guidelines for retaining walls in hill areas.
- BS EN 1997-1 (Eurocode 7): geotechnical design, which replaced the older BS 8002 in the UK.
- AASHTO LRFD Bridge Design Specifications (USA): earth pressure, MSE walls and anchored walls for highway structures.
- ACI 318 and IS 456: structural design of the concrete members.
- FHWA guidance (USA): MSE walls, soil nail walls and ground anchors.
Inspecting and maintaining a retaining wall
Check the wall once a year and after every major storm. A five-minute walk along the wall catches most problems early.
- Clear weep holes and drain outlets, and confirm that water flows after rain.
- Mark cracks with pencil and date, and measure the width with a crack gauge or a coin.
- Hang a plumb line from the top to check for tilt.
- Look at the ground behind the wall for cracks, dips or new damp patches.
- Look in front of the toe for heave, scour or wet ground.
- Probe timber for rot. Check gabion wire for rust or broken mesh.
- Keep trees with large roots away from the wall, and keep downspouts and irrigation away from the backfill.
- Reseal joints and repair spalled concrete before water reaches the steel.
Retaining wall FAQ
What is a retaining wall in simple terms?
A retaining wall is a structure that holds soil back where the ground changes level. It stops the higher soil from sliding or washing onto the lower side, using its own weight, structural strength, reinforcement in the soil or anchors in the ground.
What are the main types of retaining walls?
The 12 common types are gravity, cantilever, counterfort, buttress, gabion, crib, mechanically stabilised earth (MSE), segmental block, sheet pile, bored pile, anchored and soil nail walls. They fall into four groups: weight-based, frame-based, reinforced soil, and embedded or anchored walls.
Which type of retaining wall is best?
No single type is best. Gravity, block and gabion walls suit heights up to about 3 m. Cantilever and MSE walls cover roughly 3 to 8 m. Counterfort, MSE and anchored walls handle taller cases, and pile, nail or anchored systems fit sites where you cannot excavate behind the wall.
How tall can a retaining wall be without an engineer?
Rules differ by location. Many authorities ask for a permit and engineered design once a wall passes about 1 to 1.2 m (3 to 4 ft), or if there is a slope, driveway or building above it. Check with your local building office before you start.
Why do retaining walls fail?
Most failures come from water trapped behind the wall, a weak or poorly prepared foundation, clay or loosely compacted backfill, and loads the designer did not allow for, such as a new driveway above the wall. Water alone can roughly double the horizontal force.
Do retaining walls need weep holes?
Yes, unless the wall has another way to drain, such as a gravel drain with a perforated pipe running to an outlet. A solid wall with no drainage lets water pressure build up behind it. Weep holes are commonly 75 to 100 mm wide and spaced about 1.5 to 3 m apart.
What is the cheapest type of retaining wall?
For low walls, gabion, segmental block or stone gravity walls are usually cheapest. For tall fills, MSE walls usually cost least per square metre of face. For deep cuts with no room behind, soil nails are often cheaper than piles. Local labour, stone and material prices can change the order.
How long does a retaining wall last?
Reinforced concrete walls are commonly designed for 50 to 100 years. Segmental block and well-coated gabion walls often last several decades if they drain well. Timber walls typically last 15 to 30 years, depending on treatment and moisture.
Key points
- A retaining wall holds soil at a level change through weight, bending strength, reinforced soil, or embedded and anchored systems.
- Earth pressure is zero at the top, greatest at the base, and rises with the square of the height.
- Pick by height, room behind the wall, ground at the base, groundwater and load above.
- Water behind the wall is the largest single cause of trouble, and it can double the load.
- Build the drain, check the foundation, and call an engineer for tall or loaded walls.
This article gives general engineering information. Heights, factors and sizes are typical values for planning. A qualified engineer should design any wall that supports a road, a building, a slope or a tall fill.
Updated October 2026.