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!
Steven schrieb:
Hello tim
The concrete mixer will most likely be able to drive onto your property, unless there are obstacles that make this impossible. The ground has just dried out, so sinking is unlikely.
However, calculate beforehand how much concrete you will need. For 2 to 3 m³ (2.6 to 3.9 cubic yards), ready-mix concrete may not be economical. From 5 m³ (6.5 cubic yards) upwards, even with a small quantity, it usually makes sense.
StevenGreat, thank you very much for the advice! No, there are absolutely no obstacles; I was just unsure whether a driver would do this due to the risk of sinking, but that sounds promising. I will call the concrete plant next week to inquire. That would definitely be the easiest option.
We have just completed 37 linear meters of foundation for formwork blocks (50 cm wide x 25 cm high x 17.5 cm deep) for a retaining wall behind the terrace. On the front side, however, it will be faced with brick, so the base is quite wide at 40 cm (15.7 inches).
For the strip foundation alone, we needed two concrete mixer trucks, each delivering 4.5 m³ (5.9 yd³). The job really requires 3 to 4 helpers. One truck extended the chute with a 5 m (16.4 ft) pipe; the other, shown here, extended the chute and mixed the concrete on-site to a nice fluid consistency so it could be worked in with shovels.
There will still be plenty of shoveling to do later for the blocks themselves.
Instead of using a formwork head at the top, the builders adapted the formwork blocks at the bottom to the slope of the ground. After the foundation had dried, the top blocks were placed onto the new concrete bed. Then two rows of formwork blocks, about 50 cm (20 inches) high, were stacked on top. The vertical reinforcement is still missing in the photo.
For the strip foundation alone, we needed two concrete mixer trucks, each delivering 4.5 m³ (5.9 yd³). The job really requires 3 to 4 helpers. One truck extended the chute with a 5 m (16.4 ft) pipe; the other, shown here, extended the chute and mixed the concrete on-site to a nice fluid consistency so it could be worked in with shovels.
There will still be plenty of shoveling to do later for the blocks themselves.
Instead of using a formwork head at the top, the builders adapted the formwork blocks at the bottom to the slope of the ground. After the foundation had dried, the top blocks were placed onto the new concrete bed. Then two rows of formwork blocks, about 50 cm (20 inches) high, were stacked on top. The vertical reinforcement is still missing in the photo.
Otus11 schrieb:
We recently completed 37 linear meters (about 121 feet) of strip foundation for formwork blocks (50 cm wide x 25 cm high x 17.5 cm deep) for a retaining wall behind our terrace. In our case, the front will be finished with brickwork, so the base is about 40 cm (16 inches) wide.
For just the strip foundation, we used two concrete mixer truck loads of 4.5 m3 (about 160 cubic feet) each. You need 3-4 helpers for a job like this.
One truck had its chute extended with a 5 m (16 ft) pipe; the truck shown in the picture also had an extended chute, and on site we mixed the concrete to a nice fluid consistency for easier shoveling.
You can still shovel yourself later enough for placing the blocks
Instead of using a formwork head on top, the builders adapted the formwork blocks at the bottom to the slope of the ground, then after the foundation dried, they placed new blocks on top onto the fresh concrete bed; then two rows of formwork blocks were added on top for about 50 cm (20 inches) height. The vertical reinforcement is not shown in the picture.That looks great and is very similar to what I have in mind – the only difference being that we need to cascade the foundation in 4-5 steps because our plot has a slight slope. I want to pour the steps so that each level matches exactly the height of one row of formwork blocks.
If I may ask – how did you excavate your strip foundation? With a mini excavator using a very narrow bucket?
Otus11 schrieb:
Dug it myself – due to numerous drainage pipes.
The most fun was the compacted silt layer at 30-60cm (12-24 inches) depth.Wow, okay, 37 meters (121 feet)... That’s something.
How deep did you go? 80? 100?
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