ᐅ Retaining wall with strip foundation and cascading formwork blocks
Created on: 30 May 2018 08:45
T
tim2111
Hello everyone,
I have the following project in my garden:
There is a slight slope across our property, approximately 1.20 meters (4 feet) from the front right to the back left. To nearly level this out, I would like to build a retaining wall along the right side and the back of the property, fill it from the inside, and thereby raise the ground level. In this region, retaining walls up to 1 meter (3.3 feet) high can be built without a building permit / planning permission, so I want to keep just under this height.
At first, I planned to hire a landscaping contractor and use L-shaped steel anchors for the wall. However, based on the quotes I received and because I also want to install a double-wire mesh fence on top of the retaining wall, I am now considering doing the project myself.
I have already done quite a bit of reading and research and plan to proceed as follows:
- Excavation and installation of a strip foundation along the property boundary, approximately 80 cm (31 inches) deep to frost-free depth. The total length is about 30 meters (98 feet) on the right side and 25 meters (82 feet) at the back.
- Building the wall with formwork blocks and filling them with concrete including reinforcement.
- From a structural point of view, this should be feasible for a maximum height of 1 meter (3.3 feet) without special load requirements (no traffic or similar) and an 80 cm (31 inches) strip foundation, based on what I have read. Would you have any concerns here?
- After placing the formwork blocks but before pouring the concrete, I would set the fence posts directly in the formwork blocks and cast them in.
How should I handle the foundation considering the slope? My idea is to step the foundation in 20 cm (8 inches) increments—the height of one formwork block—so that at the front end of the property the strip foundation is at ground level (and I would cast the fence directly there). Then, as the terrain slopes downward, the strip foundation would step down in 20 cm increments following the natural slope. Accordingly, I would install the 20 cm high formwork blocks in steps with the descending terrain so that in the end I have a level wall. For this, I would need to cascade the foundation stepwise. How would you approach this? The soil is very firm and clayey, so I plan to pour the strip foundation directly into the excavated ground and only form (shape) the top few centimeters to create a clean finish.
What do you think?
Looking forward to your tips and advice!
I have the following project in my garden:
There is a slight slope across our property, approximately 1.20 meters (4 feet) from the front right to the back left. To nearly level this out, I would like to build a retaining wall along the right side and the back of the property, fill it from the inside, and thereby raise the ground level. In this region, retaining walls up to 1 meter (3.3 feet) high can be built without a building permit / planning permission, so I want to keep just under this height.
At first, I planned to hire a landscaping contractor and use L-shaped steel anchors for the wall. However, based on the quotes I received and because I also want to install a double-wire mesh fence on top of the retaining wall, I am now considering doing the project myself.
I have already done quite a bit of reading and research and plan to proceed as follows:
- Excavation and installation of a strip foundation along the property boundary, approximately 80 cm (31 inches) deep to frost-free depth. The total length is about 30 meters (98 feet) on the right side and 25 meters (82 feet) at the back.
- Building the wall with formwork blocks and filling them with concrete including reinforcement.
- From a structural point of view, this should be feasible for a maximum height of 1 meter (3.3 feet) without special load requirements (no traffic or similar) and an 80 cm (31 inches) strip foundation, based on what I have read. Would you have any concerns here?
- After placing the formwork blocks but before pouring the concrete, I would set the fence posts directly in the formwork blocks and cast them in.
How should I handle the foundation considering the slope? My idea is to step the foundation in 20 cm (8 inches) increments—the height of one formwork block—so that at the front end of the property the strip foundation is at ground level (and I would cast the fence directly there). Then, as the terrain slopes downward, the strip foundation would step down in 20 cm increments following the natural slope. Accordingly, I would install the 20 cm high formwork blocks in steps with the descending terrain so that in the end I have a level wall. For this, I would need to cascade the foundation stepwise. How would you approach this? The soil is very firm and clayey, so I plan to pour the strip foundation directly into the excavated ground and only form (shape) the top few centimeters to create a clean finish.
What do you think?
Looking forward to your tips and advice!
Hello tim,
So far, your plan is coherent and well thought out.
Don’t skimp on the reinforcement. Apply two #8 (26 mm) rebar rods horizontally on the concrete blocks. Also, place as much vertical reinforcement as possible. You will need to measure very precisely. The concrete blocks don’t have particularly large openings, especially considering that you are offsetting them during installation.
Consider whether you want to form the foundation all at once and then order ready-mix concrete. It’s not much more expensive, and if you factor in your own and possibly your helpers’ time, it can even be cheaper. Plus, you get a monolithic foundation, which is always better than patchwork.
Steven
So far, your plan is coherent and well thought out.
Don’t skimp on the reinforcement. Apply two #8 (26 mm) rebar rods horizontally on the concrete blocks. Also, place as much vertical reinforcement as possible. You will need to measure very precisely. The concrete blocks don’t have particularly large openings, especially considering that you are offsetting them during installation.
Consider whether you want to form the foundation all at once and then order ready-mix concrete. It’s not much more expensive, and if you factor in your own and possibly your helpers’ time, it can even be cheaper. Plus, you get a monolithic foundation, which is always better than patchwork.
Steven
Great, thank you all again for your advice!
One more question: for a wall height of 1 meter (3.3 feet), which type of formwork blocks would you recommend? 17.5 cm (7 inches) thickness (which I am currently leaning towards, but is that sufficient?), 24 cm (9.5 inches), or even thicker, with a 30 cm (12 inches) wall thickness?
One more question: for a wall height of 1 meter (3.3 feet), which type of formwork blocks would you recommend? 17.5 cm (7 inches) thickness (which I am currently leaning towards, but is that sufficient?), 24 cm (9.5 inches), or even thicker, with a 30 cm (12 inches) wall thickness?
We excavated the foundation and set up the formwork. We picked up scrap mesh from the steel supplier—5 pieces measuring 600x30cm (approximately 236x12 inches)—which we placed into the foundation for a small tip.
The next day, we had 2.5m³ (3.3 cubic yards) of ready-mix concrete delivered with a 3 to 4-hour delay, and we even set the first row of exposed concrete blocks directly into the wet concrete. Then we hammered in 10mm (0.4 inch) thick rods into the foundation.
This way, two of us completed a 10x1 meter (33x3 foot) wall, including filling, within 5 hours.
If the length is more than 10–20 meters (33–66 feet), I would pour the foundation in one go using regular concrete, as it flows better over longer distances.
The next day, we had 2.5m³ (3.3 cubic yards) of ready-mix concrete delivered with a 3 to 4-hour delay, and we even set the first row of exposed concrete blocks directly into the wet concrete. Then we hammered in 10mm (0.4 inch) thick rods into the foundation.
This way, two of us completed a 10x1 meter (33x3 foot) wall, including filling, within 5 hours.
If the length is more than 10–20 meters (33–66 feet), I would pour the foundation in one go using regular concrete, as it flows better over longer distances.
Hello everyone,
since the weather has cooled down a bit recently, I will take some time off in the next few days to start the project.
Thank you for your valuable tips!
I have one more question, as I am actually considering ordering ready-mix concrete at least for the strip foundation to pour it all at once. I will then fill the formwork blocks "at a relaxed pace" with concrete mixed on site.
My foundation stretches just over 50 meters (164 feet) along two sides of my property. The land is still completely undeveloped at the moment, and the soil is currently rock hard due to the dry conditions, though that may change. How can I get the ready-mix concrete from the street (running along the front of the property) to the other two sides? Do you think a concrete mixer truck could enter the property?
Or would you suggest a different solution? Using a wheelbarrow would, of course, be a lot of work...
But renting a pump would significantly increase the costs for my garden wall.
since the weather has cooled down a bit recently, I will take some time off in the next few days to start the project.
Thank you for your valuable tips!
I have one more question, as I am actually considering ordering ready-mix concrete at least for the strip foundation to pour it all at once. I will then fill the formwork blocks "at a relaxed pace" with concrete mixed on site.
My foundation stretches just over 50 meters (164 feet) along two sides of my property. The land is still completely undeveloped at the moment, and the soil is currently rock hard due to the dry conditions, though that may change. How can I get the ready-mix concrete from the street (running along the front of the property) to the other two sides? Do you think a concrete mixer truck could enter the property?
Or would you suggest a different solution? Using a wheelbarrow would, of course, be a lot of work...
But renting a pump would significantly increase the costs for my garden wall.
Hello tim
The concrete mixer will most likely drive onto your property, unless there are obstacles preventing this. The ground has just dried out, so sinking in is unlikely.
However, calculate how much concrete you will need beforehand. For 2–3 m³ (2.6–3.9 cubic yards), ready-mix concrete may not be cost-effective. For 5 m³ (6.5 cubic yards) or more, even with a smaller quantity, it usually makes sense.
Steven
The concrete mixer will most likely drive onto your property, unless there are obstacles preventing this. The ground has just dried out, so sinking in is unlikely.
However, calculate how much concrete you will need beforehand. For 2–3 m³ (2.6–3.9 cubic yards), ready-mix concrete may not be cost-effective. For 5 m³ (6.5 cubic yards) or more, even with a smaller quantity, it usually makes sense.
Steven
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