Retaining walls are common features of many homes, designed to hold back soil and create level surfaces to maximise usable space in your yard.
Whether used for residential, commercial, or infrastructure projects, they offer many benefits, such as stabilising slopes, creating terraced gardens, preventing land erosion, and enhancing the aesthetics of outdoor spaces.
Below, we explore everything you need to know about these structures, including types of retaining walls, the construction process, and long-term maintenance.
- Types of retaining walls
- How much do retaining walls cost?
- Factors to consider when choosing a retaining wall
- Design and construction process
- Maintenance and repair of retaining walls
- Choosing the right professional
- Questions to ask your tradesperson
Types of Retaining Walls
Gravity Retaining Walls
Gravity retaining walls rely on their sheer weight and mass to resist the pressure exerted by the soil behind them. These walls are constructed using heavy materials such as concrete, stone, or masonry. They’re suitable for low to medium heights and are relatively easy to design and build.
Keep in mind they require a stable foundation and proper drainage to ensure their effectiveness. Pros include cost-effectiveness and simplicity, while cons can include limited height capabilities and the need for periodic maintenance.
Cantilever Retaining Walls
Cantilever retaining walls are designed with a reinforced concrete structure, featuring a horizontal base or footing, a vertical stem, and a horizontal projection known as the toe. The stem and toe work together to resist the soil pressure and provide stability. This type of retaining wall is commonly used for moderate to high heights and can support heavy loads.
Cantilever walls offer structural strength and versatility but require professional engineering and careful consideration of design elements such as base size, stem thickness, and reinforcement placement.
Sheet Pile Retaining Walls
Sheet pile retaining walls are constructed using interlocking steel, vinyl, or wood sheets driven into the ground. These sheets create a barrier against soil pressure and are commonly used in waterfront or marine applications. Sheet pile walls are known for their flexibility, as they can be installed vertically or at a slight angle. They’re suitable for both temporary and permanent structures, but they may need additional measures such as anchors or tiebacks for added stability.
Anchored Retaining Walls
Anchored retaining walls are built to withstand sideways pressure from soil by using anchors or tiebacks. These anchors go horizontally into the soil behind the wall and are connected to the wall with cables or rods.
Anchored retaining walls work well when there isn't much space or when there’ll be strong sideways forces, and they’re more stable and can be taller than other types of walls. It’s important to be aware that designing and installing them requires specialised engineering and expertise.
Learn more: Our 7 Favourite Retaining Wall Designs
How much do retaining walls cost?
The cost of retaining walls in Australia can vary significantly depending on various factors such as the type of retaining wall, materials used, height and length of the wall, site conditions, labour costs, and location. Here are some estimates:
- Gravity retaining walls: Typically range from $200 to $600 per square metre. Factors such as the choice of materials (concrete, masonry, stone), wall height, and site conditions can influence the overall cost.
- Cantilever retaining walls: Cantilever retaining walls are generally more expensive due to the complexity of design and construction. On average, the cost can range from $500 to $1,500 per square metre, depending on the materials used (reinforced concrete) and wall height.
- Sheet pile retaining walls: The cost can range from $400 to $1,200 per square metre, depending on factors such as the type of sheet piles (steel, vinyl, wood) and the need for additional measures like anchors.
- Anchored retaining walls: Anchored retaining walls are considered a specialised type of retaining wall and are typically more expensive. The cost can range from $800 to $2,000 per square metre, depending on factors such as the number of anchors, depth of anchoring, and wall height.
It's important to obtain detailed quotes from experienced contractors or engineers who can assess your specific project requirements and provide accurate cost estimates. Additionally, keep in mind that these costs do not include potential expenses for site preparation, excavation, drainage systems, or any additional landscaping or finishing touches.
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Factors to Consider when Choosing a Retaining Wall
When choosing a retaining wall for your project, you should take several things into account:
- Height and load requirements: Determine the height of the wall and the loads it will need to support. Different types of retaining walls have varying height limitations and load-bearing capacities.
- Soil conditions and drainage: Assess the soil type and conditions on the site. The soil's properties, including cohesion, friction angle, and permeability, will influence the design and construction methods. Proper drainage systems should also be considered to prevent water buildup behind the wall.
- Aesthetic considerations: Retaining walls can significantly impact the visual appeal of a space. Consider the desired aesthetic style, such as natural stone, textured concrete, or timber, to complement the surrounding environment.
- Cost and maintenance: Evaluate the project budget and ongoing maintenance requirements. Some types of retaining walls may be more cost-effective upfront but require regular maintenance, while others may have higher initial costs but lower long-term maintenance needs.
Design and Construction Process
The design and construction of a retaining wall involve several key steps:
- Site evaluation and analysis: A thorough assessment of the site includes soil testing, topographical survey, and analysis of existing structures or features that may impact the design.
- Engineering and design: A professional engineer or landscaper will create a detailed design plan that considers factors such as soil conditions, load requirements, drainage systems, and aesthetic preferences.
- Permitting and regulatory requirements: Check local regulations and obtain the necessary permits for constructing a retaining wall. Compliance with building codes and safety standards is crucial to ensure a structurally sound and legally compliant installation.
- Excavation and preparation: The site will be prepped by clearing vegetation, excavating the area, and levelling the ground. Proper compaction of the soil is crucial for creating a stable foundation.
- Construction techniques: Construction will begin based on the specifications, which can include pouring concrete, stacking stones or blocks, driving sheet piles, or installing anchor systems.
- Drainage and backfilling: Appropriate drainage systems will be included to prevent water accumulation behind the wall, which could compromise its stability. The space behind the wall is backfilled with suitable materials, ensuring proper compaction to provide additional support.
Learn more: How Can I Landscape a Sloping Backyard?
Maintenance and Repair of Retaining Walls
To promote the longevity and functionality of retaining walls, regular maintenance and timely repairs are essential. Here are some key aspects to consider:
- Regular inspections: Conduct periodic inspections of the retaining wall to identify any signs of damage or structural issues. Look for cracks, bulges, leaning, or excessive settlement.
- Cleaning and vegetation control: Keep the wall and surrounding area free from debris, dirt, and vegetation. Overgrown plants can exert additional pressure on the wall or compromise its integrity.
- Repairing cracks and damage: Address any cracks or damage quickly to prevent further deterioration. Small cracks can be repaired using suitable sealants or patching materials, while significant structural issues may require professional assessment and repair.
- Replacing or reinforcing failing walls: If a retaining wall shows signs of severe damage or instability, it may need to be replaced or reinforced. Talk to a qualified retaining wall expert to evaluate the best course of action based on the specific conditions and requirements.
Choosing the Right Professional
Determining the most suitable contractor for installing a retaining wall means finding someone who can complete the job to the highest standard within your budget.
Here’s how to find the best contractor to make your retaining wall ideas a reality:
1. Get Several Quotes
Enter the information outlining your job on Service.com.au, and we'll provide you with a list of local tradespeople who can help do the job.
2. Narrow Down Your Options
Service.com.au uses a three-tier badge system to help you make the best choice.
We recommend selecting a tradesperson with the highest level (badge 3 – ‘recommended’) from our three-step verification process.
3. Do Further Research
Once you’ve narrowed down your choices, check out the company’s online presence to get an idea of its reputation and service offering. View their website and social media pages to see customer reviews and the quality of their work in photos.
Questions to Ask Your Tradesperson
Here are some questions that can be helpful to ask when hiring a tradie for your job:
- Can you provide references from previous work?
- Are you licensed and insured?
- How long have you been in business?
- Do you have specific experience installing certain types of retaining walls?
- How do you communicate with customers during the process?
- Are you flexible with your schedule, and can you work on weekends if necessary?
What permits are needed for constructing a retaining wall?
The permit requirements for constructing a retaining wall in Australia can vary depending on factors such as the height and location of the wall. In most cases, you will need to check with your local council or relevant government authority to determine the specific permits and approvals required for your project. It's essential to comply with local building codes, regulations, and planning requirements. Consulting with a professional engineer or builder experienced in retaining wall construction can help ensure you obtain the necessary permits and meet all legal obligations.
Can I build a retaining wall myself, or do I need professional help?
While it may be possible to construct a small, low-height retaining wall as a DIY project, it is generally recommended to seek professional help for larger or more complex retaining wall installations. Retaining walls require careful design, proper engineering, and construction techniques to ensure their stability, longevity, and compliance with building codes. Professional engineers or licensed builders have the expertise to assess site conditions, design an appropriate wall, and implement the necessary measures for construction, drainage, and reinforcement. Engaging professionals can help avoid potential issues and ensure a safe and successful retaining wall project.
How long do retaining walls typically last?
The lifespan of a retaining wall can vary depending on factors such as the materials used, construction quality, site conditions, and maintenance. Well-constructed retaining walls using durable materials like concrete or reinforced masonry can last for several decades. In general, a properly designed and maintained retaining wall can be expected to last 30 to 50 years or more. However, it's important to note that poor construction, inadequate drainage, or failure to address site-specific factors may significantly reduce the lifespan of a retaining wall. Regular inspections, proper maintenance, and timely repairs can help extend the lifespan of a retaining wall.
What are some common signs of a failing retaining wall?
Recognising the signs of a failing retaining wall is crucial to address issues before they become more severe or dangerous. Some common signs of a failing retaining wall include:
- Cracks: Visible cracks in the wall, particularly those that are widening or accompanied by movement, may indicate structural problems.
- Leaning or bulging: If the retaining wall is leaning or bulging outward, it suggests instability and potential failure.
- Soil erosion or settlement: Excessive soil erosion or settlement behind the wall may indicate drainage issues or poor compaction, compromising the wall's integrity.
- Tilting or sinking: If the top of the wall is tilting or sinking, it may be a sign of inadequate foundation or poor construction.
- Water accumulation: Persistent water accumulation behind the wall can weaken the structure over time and lead to failure.
If you notice any of these signs, it is important to consult a professional experienced in retaining wall assessment and repair to evaluate the situation and recommend appropriate actions.
Are there any alternative solutions to retaining walls?
Yes, there are alternative solutions to traditional retaining walls, depending on the specific requirements and site conditions. Some alternatives include:
- Terracing: Creating terraced levels using gentle slopes or steps can help manage soil erosion and create usable space while reducing the need for tall retaining walls.
- Slope stabilisation techniques: Techniques such as erosion control mats, geotextiles, and bioengineering methods can be used to stabilise slopes and prevent soil erosion.
- Gabion walls: Gabion walls use wire mesh baskets filled with stones or rocks to provide structural support and drainage. They can be an effective alternative to traditional retaining walls in certain situations.
- Soil nailing: Soil nailing involves inserting reinforcing elements such as steel bars or grouted anchors into the slope to increase its stability.
- Reinforced soil systems: Reinforced soil systems, such as geogrid or geosynthetic reinforcements, can be used to reinforce soil and create stable structures without the need for conventional retaining walls.
The suitability of alternative solutions depends on factors such as site conditions, load requirements, and aesthetic preferences.
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All the costs quoted were sourced at the time this article was written. They are to be used as an AUD cost guide and may vary locally, and are subject to market changes.