As an engineering firm, we understand the vital role retaining walls play in managing rainfall and providing stability during earthquake events. With clients increasingly seeking advice on retaining wall options, we've decided to dive into this topic and help you make an informed decision.
In our Retaining Wall Series, we discussed the growing importance of retaining walls and when a Building Consent is necessary. To gain a deeper understanding, we recommend reading the following articles:
Retaining Walls are Getting Bigger: https://www.dtce.co.nz/post/retaining-walls-are-getting-bigger
When Do I Need a Building Consent for My Retaining Wall: https://www.dtce.co.nz/post/when-does-your-retaining-wall-need-building-consent
Choosing the Right Retaining Wall type
To assist building owners and architects in making an informed choice, we've compiled a list of common retaining wall types and their strengths and weaknesses. Additionally, we've included a brief overview of the construction process for each type, as well as recommendations for different slope heights.
For easier navigation, click one of the three heights below to be taken to the specific section:
1.0m Cut Height
Engineered timber pole wall - 1.0m
Suitable for: landscaping walls, boundary walls, driveways
Cut height limitations: 2.0 meters depending on site conditions
Maintenance requirements: little to none
Materials: easily handled on-site
This wall type has a relatively straightforward construction process:
Auger holes
Engineer construction monitoring site visit
Place timber poles in holes
Pour concrete foundation
Install lagging & drainage
Engineer construction monitoring site visit
Back fill
Engineered block wall with toe footing - 1.0m
Suitable for: subfloor walls, foundation walls, landscaping walls, boundary walls, driveways
Cut height limitations: 2.5 - 3.0 meters depending on site conditions
Maintenance requirements: little to none
Material handling: easily handled on-site
This wall type has a relatively straightforward construction process:
Excavate foundation
Place foundation reinforcing
Engineer construction monitoring site visit
Pour concrete foundation
Layer blocks with wall reinforcing and install drainage
Engineer construction monitoring site visit
Fill the wall core with grout
Backfill
Engineered block wall with heel footing - 1.0m
Suitable for: sites that require a lot of fill i.e cut to fill sites
Cut height limitations: 2.5-3.0m depending on site conditions
Maintenance requirements: little to none
Material handling: easily handled on-site
Heel walls rely on fill soil on the footing for stability and generally result in a smaller foundation. This wall type has a relatively straightforward construction process:
Excavate foundation
Place foundation reinforcing
Engineer construction monitoring site visit
Pour concrete foundation
Layer blocks with wall reinforcing and install drainage
Engineer construction monitoring site visit
Fill the wall core with grout
Backfill
2.0m Cut Height
Engineered timber pole wall - 2.0m
Suitable for: landscaping walls, boundary walls, driveways
Cut height limitations: 2.0 meters depending on site conditions
Maintenance requirements: little to none
Materials: moderately difficult to handle on-site
This wall type has a relatively straightforward construction process similar to 1m high:
Auger holes
Engineer construction monitoring site visit
Place timber poles in holes
Pour concrete foundation
Install lagging & drainage
Engineer construction monitoring site visit
Back fill
Engineered block wall with toe, heel, and shear key - 2.0m
For taller cut heights or restricted footing space, heel and shear key may be necessary.
Suitable for: Basement walls, garage walls, and walls integral to building
Cut height limitations: 2.5-3.0m
Maintenance requirements: little to none
Materials: easily handled on-site
This wall type has a relatively straightforward construction process:
Excavate footing, heel and shear key
Place foundation reinforcing
Engineer construction monitoring site visit
Pour concrete foundation
Lay blocks with wall reinforcing and install drainage
Engineer construction monitoring site visit
Fill the wall core with grout
Backfill
Non-engineered spray concrete wall - 2.0m
This wall type does not retain soil but can reduce the chance of a slip by keeping soil as dry as possible
Suitable for: a relatively cheap non-retained solution for exposed soil banks
Cut height limitations: 2.0m
Maintenance requirements: ongoing to ensure excess water drains properly
Materials handling: requires specialist contractor and occasionally scaffolding
This wall type has a moderately difficult construction process due to the requirement of a specialist contractor and scaffolding:
Clear vegetation and contour the soil bank
Place mesh reinforcing and drainage
Engineer construction monitoring site visit
Spray concrete
3.0m+ Cut Height
Engineered timber pole wall with ground anchors - 3.0m
Ground anchors are needed for taller cut heights to prevent the wall from overturning, but can result in shallower foundations. Anchors crossing boundary lines will require consent from neighboring properties.
Suitable for: landscaping walls, boundary walls, driveway walls
Cut height limitations: 3.0 meters
Maintenance requirements: ongoing maintenance for exposed steel fixings
Material handling: difficult to handle on-site due to size of timber poles
This wall type has a relatively straightforward construction process:
Augur holes
Engineer construction monitoring site visit
Place timber poles in holes
Pour concrete foundation
Install anchors and walers
Install lagging and drainage
Engineer construction monitoring site visit
Backfill
Engineered timber pole wall with ground geogrid - 3.0m
Suitable for sites that require a lot of fill i.e cut to fill sites
Suitable for: landscaping walls and driveway walls
Cut height limitations: 3.0 meters
Maintenance requirements: ongoing maintenance for exposed steel fixings
Material handling: difficult to handle on-site due to size of timber poles
This wall type has a relatively straightforward construction process:
Augur holes
Engineer construction monitoring site visit
Place timber poles in holes
Pour concrete foundation
Install lagging and drainage
Partially backfill to geogrid level
Install geogrid and walers
Engineer construction monitoring site visit
Complete backfill
Engineered timber pole wall with deadman - 3.0m
Suitable for: landscaping walls, boundary walls, and driveway walls
Cut height limitations: 3.0 meters
Maintenance requirements: ongoing maintenance for exposed steel fixings
Material handling: difficult to handle on-site due to size of timber poles
This wall type has a relatively straightforward construction process:
Augur holes
Engineer construction monitoring site visit
Place timber poles in holes
Pour concrete foundation
Install lagging and drainage
Excavate deadman
Place reinforcing for deadman
Engineer construction monitoring site visit
Pour concrete deadman
install walers
Backfill and fill overtop of deadman
Engineered sprayed and anchored wall - 3.0m+
Sprayed and anchor walls are typically used for taller cut heights exceeding 3.0m. Anchors crossing boundary lines will require consent from neighbouring properties.
Suitable for: boundary walls
Cut height limitations: over 3 meters
Maintenance requirements: ongoing maintenance for exposed steel fixings
Material handling: moderately difficult to handle on site due to anchors
This wall type has a moderately complex construction process that generally follows:
Clear vegetation and contour the soil bank
Install anchors and anchor heads
Place mesh reinforcing and drainage
Engineer construction monitoring site visit
Spray concrete
Engineered block wall with pilasters - 3.0m+
Pilasters (reinforced block columns) are typically used for taller block walls to add strength. A heel and shear key may also be necessary to prevent overturning and sliding.
Suitable for: basement walls, garage walls, and walls integral to the building
Cut height limitations: over 3 meters
Maintenance requirements: little to none
Material handling: easily handled on-site
This wall type has a relatively straightforward construction process that generally follows:
Excavate footing, heel, and shear key
Place foundation reinforcing
Engineer construction monitoring site visit
Pour concrete foundation
Lay blocks with wall reinforcing and install drainage
Fill the wall core with grout
Engineer construction monitoring site visit
Backfill
Pinned block wall with concrete slab - 3.0m+
Connecting block walls to a concrete floor slab and the top can allow the wall to be used for taller cut heights
Suitable for: basement walls, garage walls, and walls integral to the building
Cut height limitations: over 3 meters
Maintenance requirements: little to none
Material handling: easily handled on-site
This wall type has a relatively straightforward construction process that generally follows:
Excavate footing, heel, and shear key
Place foundation reinforcing
Engineer construction monitoring site visit
Pour concrete foundation
Lay blocks with wall reinforcing and install drainage
Engineer construction monitoring site visit
Fill the wall core with grout and backfill
Place reinforcing slab for above
Engineer construction monitoring site visit
Pour concrete slab
Over 3.0m High
Once a cut height is above 3.0m, the design of the retaining wall becomes more bespoke and needs expert geotechnical advice. For these types of projects we can help design, or work closely with other geotechnical consultants to help you make the right decisions.
Selecting the right retaining wall type is crucial for maintaining the stability and integrity of your property.
By considering factors such as slope height and project requirements, you can make an informed decision that will stand the test of time. Our experienced team of structural engineers are always available to help you navigate the complexities of retaining wall design and construction.
Contact us for personalised guidance on your project.
Comments