- Effective planning is important for the success of any construction project, and retaining walls are not an exception.
- There are no shortcuts. Build your retaining wall correctly the first time.
- Attractively built retaining walls can actually increase the value of your property
- Retaining walls can create a lot of more productive space in your yard if designed and placed correctly
- Retaining walls can prevent the unnecessary expense for the importation of new topsoil to repair damage caused by erosion and soil slippage
- Two separate retaining walls lower in height may actually be more effective, more attractive and be safer than one higher wall --and create more useful space in the process. An additional access stairway between the two walls may be an option to consider.
- If an exceptionally high retaining wall is required or extremely unstable ground conditions are suspected, consider an engineered solution for your specific site conditions for safety and a more successful outcome.
- For any lower stone, cement, or brick retaining wall structure that is not rigidly mortared, a crushed rock foundation is usually adequate and easily installed.
- Depending upon the manufacturer, some interlocking, stacking block types may need additional ballast for weight as total wall height may dictate. Reading the manufacturer's specifications and requirements is recommended.
- For low walls, simple "weep holes" placed in the wall may suffice for drainage, but may also eventually stain the face of the wall, depending upon the mineral content of the water in your locality.
- Plan drainage on the uphill side of the wall with free-draining granular material and weeping tile if necessary to prevent water damage to the wall. Drainage properly designed can prevent total destruction of the wall in extreme wet conditions or very heavy rainfall areas where soil is frequently in a state of total saturation and unstable.
- If surface water runoff is a serious and constant problem, consider installing a French drain where the water originates higher up the slope.
- Verify lot line clearance and municipal bylaws prior to beginning any construction. There may be height restrictions applicable; you may require an exemption from the bylaw for unusual on-site property conditions.
- If everyone on your block already has timber retaining walls, for appearance, do consider building a characteristically- comparable project to help maintain and promote 'good neighbourhood' relations.
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Is that Incoming I hear?
Thanks for the interesting article about building retaining walls. I didn’t know that an engineered solution should be used for exceptionally high retaining walls. It sounds important to know what wall would be categorized as exceptionally high especially if it determines how the wall is constructed.
Hi Taylor, first of all, welcome to Incomingbytes!
Thank you for asking that important question. Recommendations for engineered safe remedial design where higher retaining walls are required should almost be made on a case by case basis because of the high number of variables such as location, soil conditions, geographical weather conditions and the likelihood of extreme weather events.
In an extreme example, a 20′ high retaining wall adjacent to a public street not being correctly designed and engineered to consider vibration or unstable, potentially fluidized soil conditions and public safety could be a liability and prohibitively-costly mistake.
How high can a retaining wall be without likelihood of accident or failure at some time in the future? Is an engineered solution required? Can, or should a homeowner realistically make a decision for a 16′ high retaining wall independently–and be certain he has successfully met all structural requirements, safety and municipal codes ? Have his choices of foundation, materials and structural integrity eliminated any chance of accident, failure, and/or any resulting liability?
Collapse of a 6′ wall, or a tumble to a concrete sidewalk or into a street can be serious or even fatal. Let’s be realistic and say an engineered solution may not prevent those events. Engineers cannot predict the future either; at best we can only use resources available to us and reduce the potential of damage or events in the future. Common sense must be considered.
Structural problems tend to increase exponentially with retaining wall height; particularly from lateral soil pressure, stability and soil creep, ie. movement down-slope. Engineering data is available for more demanding structures, why not use it?
Footing failure, weight of the completed wall, water collection and elimination, requirements for safety barriers, extreme weather events, and other factors all must be considered.
Soil conditions are clearly the most important limitation for wall height, design and construction. Soil type, water content, soil creep, slope, and other factors such as vibration from traffic , structural materials, rate of drainage –are all factors which should be used in determination of height and necessary safety factors.
Saturation of soils under specific conditions and fluidization of soil can be a nuisance for a lower 4′ wall –but disastrous for an improperly-built 12′ wall. Discharge of water may become an issue. Proximity to sensitive waterways. Discharge of drainage water to public streets, storm sewers, or adjacent lands or private property. What is allowed? At what height and size are such practices not allowed? Are homeowners ever apprised of all municipal bylaws and engineering requirements for major projects?
The best answer to your question about engineered vs. non-engineered retaining walls where height is concerned — may be to be aware of the physical demands of your project, use common sense, and ask questions regarding limitations of bylaws at your local municipal office.
Good luck with your projects, Taylor, I hope this helps, and thanks again for visiting IncomingBytes ~R