A Guide To Better Retaining Wall Design

A Guide To Better Retaining Wall Design

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Designing a wall to reclaim your property may appear easy to others however, much like the iceberg that lies beneath, there’s plenty more happening that is hidden from view with walls for retaining than people are aware of. If you don’t have the right knowledge, care and knowledge, danger is huge.

Wall failures that fail to retain can cause significant damages to your property and services, and may even result in grave injury or death. This is why it’s recommended to construct an retaining wall that is designed by an engineer, and built by a certified retaining wall construction company to ensure a secure economical, effective and affordable wall retaining solution.

This article will expand your understanding of wall retaining from the ground to the top, going through the how, why and the how of designing a retaining wall prior to discussing the ways that engineers (us particularly) are creating more efficient design strategies which result in better results for our clients, be it homeowners or builders.

What is a retaining walls?

A wall of retaining that helps to hold soil on two levels (created through cut and fill) by retaining soil laterally while absorbing the lateral forces that are imposed by pressure from the earth.

The Perth Standard, AS4678 – Earth Retaining Structures deals specifically with walls which are:

  • Greater than 800mm, and less than 15m tall.
  • 70 degrees or more towards the horizontal (thereby exempting revetment structures having more gentle slopes).

Even for smaller, 400mm (or less) do-it-yourself or handyman home constructions, they have suggested guidelines for designing and building in regards to factors like the depth of posts, wales backfill, drainage, and batter. These can be found at the industry associations your hardware retailer. The cheapest and quickest method can cause more problems than it’s worth later Therefore, it is important to take the time to plan your project properly regardless of the scope of the task.

Why should you build a retaining wall?

Retaining walls are all over. They are not just for the construction of homes, they also have applications in a variety of different areas, for example:

  • Gardens, parks, and farms on hillsides
  • Important public works like railroad overpasses or roads
  • Mining, business and industry
  • Healthcare, education, sports and other facilities for the public.

This article focuses on wall retaining that require approval by engineers in residential environments. In particular, for example, you could require an enclosure along your property line to protect your land or that of your neighbor or cut and build beneath the foundation of a house or a basement, plant your garden or create a filler and soil to make a larger backyard that is flatter and wider.

What kinds of walls for retaining are there?

There are numerous types of walls for retaining, each having a distinct appearance and design. Between the wall and beneath it is the hidden complexity of their design that may comprise drain pipes, footings geotextiles, waterproofing and a variety of kinds of backfill sections and surface soils. Below are the major types of retaining walls in Perth that are used for residential building, all of which has each having its particular pros and cons.

Sleeper Walls (Timber or Concrete)

This is the “garden variety” type of wall that people imagine in their eye. Horizontal timbers (also known as concrete wales) are positioned to posts that are near vertical and inserted in concrete foundations.

Pros

  • Both are typically cost-effective.
  • It can be built in a compact space.
  • Concrete sleeper walls made of galvanized steel posts comply with the 60-year design requirement in AS4678.
  • There are numerous choices in terms of aesthetics, including timber species or coloured or pattern concrete sleepers.

Cons

  • If the ground is saline it may be difficult or impossible to build the posts or piers with bores.
  • They can’t be effectively waterproofed and water can flow through.
  • For walls with a height of over 800mm, and along an edge, getting the H5 treated wood required for the 60-year design lifetime can be a challenge and cost a lot.
  • Not all developers or councils allow timber walls to be built on borders.

Cut Stone (Sandstone) / Boulder / Gabion Walls

The walls are constructed of bulky, typically broad-based, materials that harness gravity to provide the wall with the strength and stability it needs. The gravity-based walls are in use from the beginning of time (some are still in use) However, there are some things to think about.

Pros

  • Mid-range, in terms of cost-effectiveness.
  • Ideal for installations in a shallow rock, and with limited or no footings are required.
  • Attractive aesthetic appeal

Cons

  • It is not possible to construct in a small space since gravity walls require mass and width to ensure stability.
  • This means they require more space (depth).
  • They can’t be effectively waterproofed therefore water will flow through.
  • Boulder walls can have erratic performance, especially since there could be less contact between the stones. Stone cut is usually preferred.
  • Different types of stones are readily available. Make sure you understand what you’re receiving.
  • For gabion walls it is the wire that is the weakest part. It could fail before the design’s 50-year lifespan in the event that it is not carried out by a professional.

Reinforced Concrete Block Walls

These walls make use of hollow concrete blocks that are reinforced using steel reinforcement, and then lined with cement laid. They can be built without stepbacks, which helps save space. The front wall may be designed with an attractive range of smooth or flat rendering.

Pros

  • They are able to be built in an area that is tight when using pilings that are placed under footings (if the location is appropriate).
  • More height is possible by using a heel and toe design.
  • The material can be waterproofed.
  • The aesthetic appeal of a room can be improved by rendering.
  • They are suitable for the majority of walls on residential properties, and can be integrated with the envelope of the building.

Cons

  • They are usually the most expensive choice.
  • Pier designs typically do not allow for walls that are high.
  • The design of the cantilever has a wide toe, therefore space is the preferred option in this situation. In certain situations the toe or heel might be intruding into the property of a neighbor.

Link Block Walls

These interlocking blocks are smaller and permit a range of designs, such as curved wall panels that are popular in gardens.

Pros

  • Affordably priced
  • It is suitable for installation within shallow rocks. No or little footings are needed
  • Beautifully pleasing aesthetics with a variety of colors and patterns available.
  • The smaller blocks offer more flexibility than other gravity walls.

Cons

  • It is essential to make sure that geogrid concrete or no-fines concrete is put in place behind the wall according to manufacturer specifications. Very small walls don’t require this.
  • Similar to gabion and boulder walls, they are not able to be built in a small space. Since they are gravity-type walls, the soil reinforcement required or concrete with no fines results in the wall being deeper and will require a larger footprint.
  • You must ensure that a skilled contractor or engineer is in charge to prevent problems during installation.
    There are also other kinds of wall anchors or tiebacks that are costly and used mostly in large civil works, for instance, retaining high cuttings in freeways. They are not typically employed for residential projects.

Ideas for designing a retaining wall

You (or you or your customer) have determined that a retaining walls is required. You’ve probably already had an idea of where you’d like to put the wall, how tall it is, and what you’d like it to look. To help you refine your thoughts and take the design of your retaining wall one step further there are some specific aspects to think about.

Choosing a Builder and/or Engineers

While being aware of the various kinds of retaining walls can be beneficial for your initial thoughts the majority of homeowners would require assistance from a professional. Many walls are constructed through DIY effort and sweat. They are also constructed by landscapers. Before you decide on the contractor you’ll hire to construct your wall, take into consideration the level of structural complexity.

  • We would always suggest using a builder who is licensed to construct retaining walls.
  • If the wall you’re building is higher than 800mm it’s likely to require an engineered design for your retaining wall according to AS4678 (see the Foundation Engineering Service) to make sure council approval is obtained, maximize the durability of the wall and ensure peace of peace of.
  • You can’t generally hire an engineer later on i.e. to approve an existing wall constructed. If you’re unsure it is best to talk to an engineer in the preliminary design stage, when there’s some room for innovation.

Beyond deciding the person who is going to design (design) and construct the wall, there’s many other aspects to consider such as:

Location Considerations

  • Dimensions of footprint available.
  • The slope of the ground between the wall and the ground for determining surcharge loading above the wall or submining at the bottom.
  • The wall’s proximity to structures or walls.
  • Accessibility to the area to construction.
  • The presence of trenches, services or pipelines at the wall’s base.
  • Variation in the levels of moisture across regions salt exposure, abrasive soils.
  • Developer and local authority restrictions: sometimes, these define wall types that are not allowed to be constructed; for instance that no timber sleeper walls that exceed 1m in height are allowed in Brisbane.

Soil Considerations

  • The soil properties include density as well as stiffness, reactivity salinity as well as permeability, shear strength and bearing capacity.
  • The availability of solid ground to build the foundation.
  • Groundwater presence.

Load Considerations

  • End of Serviceability or Ultimate Limit Statesthe point where sliding on the bottom of the structure, the rotation of the structure, or rupture of connections or components can occur.
  • Earth pressure.
  • Hydrostatic loads.
  • Charge loads that are above the wall, such as structures or vehicles.
  • Wind can carry loads.
  • Earthquake load.

Design Considerations

  • Design life required.
  • Height and length are required.
  • Surcharge loads that are applied over the walls (including live loads, such as roads or dead loads, like buildings).
  • Aesthetics, wall batters or setback.
  • Material properties, such as the durability and strength of grouts and mortars, concrete posts, or sleepers and sleepers made of timber (pre-treatment to prevent termite and fungus).
  • Drainage
  • What will be the expected or likely flow of water and how is it addressed? The considerations must be taken into account for both the design of the wall and for landscaping over the wall.
  • Backfilling with information about the type, quantity and location.
  • Access to monitoring and maintenance.
  • Security during construction.
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