Retaining Wall Design and Construction
Retaining walls add depth and usable space to a good landscape design. Well constructed walls hold back soil that would otherwise slump into an unusable slope. This creates more useful space and adds a pleasing architectural feature to the area if designed well. Retaining wall construction is used anywhere a sloped landscape needs to be made flat with minimal loss of usable space. DirtWright offers retaining wall repair, design, and construction as a core portion of our hardscape contracting business.
Types of Retaining walls
Many materials can be used to build a retaining wall. Here’s a chart:
| Material | Advantages | Deficiencies | Construction Methods | Cost |
|---|---|---|---|---|
| Concrete | Strong if designed correctly, durable. Unlimited shapes and huge variety of finishes and colours. | Vulnerable to cracking with movement. Can deteriorate with time if concrete is not made correctly. High skill requirement. | Counterfort & buttress walls, anchor tie-backs | ++++ |
| Timber | Fast construction, readily available & somewhat renewable material. Unique texture and visual aesthetic. Typically free draining; Movement tolerant. | Wood eventually can deteriorate; limited in height. PWF treatment can be slightly toxic in some cases. Shapes are limited. | Tied back Timbers/ deadmen/MSE walls | ++ |
| Stone | Unique visual aesthetic, long lasting, natural material. Free draining. Movement tolerant. | Very high skill required to build well. Labour intensive. Stone may not be locally available. Heavy machinery often required to place rocks. | Gravity walls, MSE walls | +++++ |
| Hollow Core Block | Modular construction, huge variety of design textures and shapes, flexible & tolerant of movement. Free draining | Can be vulnerable to base deficiencies & shifting with time. | MSE walls | +++ |
| Rock Baskets | Materials often available onsite, fast, modular construction. Minor curves possible. Free draining. Movement tolerant. | Light on visual impact, heavy equipment may be required to place. Metal baskets may eventually corrode & fail | MSE Walls | +++ |
| "B" Blocks | Readily available material, fast, durable construction. Typically free draining; tolerant of some movement. | Light on visual impact, heavy equipment required to place. Limited to rectilinear construction; batter walls are not feasible. | Gravity Walls, MSE Walls | +++ |
Drainage for durability
Drainage is a crucial component of all retaining wall systems. Improperly designed drainage will weaken the soils behind the wall as well as creating hydrostatic pressure against the wall face. This is a common mode of retaining wall failure. Correct drainage pulls water away from the wall and helps limit frost jacking and other frost related damage to the wall.
Retaining Wall lateral stability
Lateral support is the other key part of a good retaining wall design. This is what keeps the wall from physically tipping over from the overturning moment exerted by the retained soils. This resistance can be provided by simply making the wall massive, as in the case of a gravity wall. More common is some form of tieback past the retained soil, as with deadmen or cable anchors. The prevalence of block walls means that mechanically stabilized earth (MSE) walls are very common. This composite wall construction uses materials like geogrid or mesh to stabilize the retained soil and connect the wall face to the stable, unsupported soils.
Retaining wall design & building code
A good retaining wall contractor knows that any size of wall will tilt and fail over time if it is not built correctly. This is unfortunately not common knowledge, nor limited to height: we’ve found walls 12″ high that are failing. Retaining walls in Alberta and other similar climates will usually fail from frost and drainage related deficiencies. Failure can be sudden, destructive, and costly to repair.
For this reason, retaining wall construction is governed by local building code. Check with your local authority, but in many jurisdictions, walls over 1.2m (4′) high at any point require permits and often engineering. Walls integral to the structure of a building are regulated by Alberta Building code and require permits regardless of height. Good structural guides are published by manufacturers such as Allen Block and Keystone, but are not a substitute for permits and engineering.
Full Service Retaining Wall Contractor
DirtWright is familiar with the variety of soils and structural options available as a Red Deer retaining wall contractor. We can manage the entire design & construction process, which has cost and continuity advantages for our clients. We’ll explain options so you can make an educated decision for the best retaining wall design for your situation. Contact us for more information