ᐅ Foundation for a 1.5-meter-high retaining wall made of large rectangular blocks.

A retaining wall 1.5 meters high (5 feet) is to be built using large ashlar stones (shell limestone). What should the foundation look like in terms of depth and material?

These stones are very heavy; is a special foundation necessary, or would, for example, a 30 cm (12 inches) layer of crushed stone beneath be sufficient?

And is drainage required? Or is a layer of crushed stone behind the retaining wall enough?

Hello Thierse

For such dimensions, I would definitely build a foundation (concrete foundation) as a stabilizing element. You have huge stones there, which you will be stacking 1.5 meters (5 feet) high. If you place the blocks on compacted gravel, I see a risk of erosion. Unless you set the stones 40–50 cm (16–20 inches) deep into the ground. That would then serve as the foundation.
I would dig 60 cm (24 inches) deep. Choose the width so that it supports the width of the blocks. Then put in 15 to 20 cm (6 to 8 inches) of gravel, compact it very well, pour the foundation, and then stack the stones.
That way, at least the bottom part of the blocks won’t move.
However, it must be a very thick wall if it is 1.5 meters (5 feet) high and the blocks are not connected to each other. I hope you know what you’re doing.

Steven

Such large rectangular blocks are very popular with homeowners. But is such a massive foundation really necessary for these stones?

We also need a retaining wall that should be 1.80 m (5.9 ft) high. The total length is 14 m (46 ft) plus a 5 m (16.4 ft) corner section. We want to build it using these concrete system blocks. One block measures 180 cm (71 inches) x 60 cm (24 inches) x 60 cm (24 inches), weighing around 1.5 tons each. So, there will be three rows stacked on top of each other.

I am still struggling with the question of the right foundation. The blocks interlock with each other and also have those "Lego"-style connectors, and the corner sections are also interlocked. Do we really need a proper concrete foundation, or would compacted frost protection gravel with a layer of lean concrete on top be sufficient?

KingSong schrieb:
We also need a retaining wall that should be 1.80 m (5 ft 11 in) high. The whole length is 14 m (46 ft) plus 5 m (16 ft) around the corner. We want to solve this with these concrete system blocks. One block would be 180 cm (71 in) x 60 cm (24 in) x 60 cm (24 in), weighing about 1.5 tons per block. So there will be 3 rows stacked. I’m also struggling with the question of the proper foundation. The blocks interlock, and they also have these "Lego" connectors, and the corner connections interlock as well. Does it really need a proper foundation, or is compacted frost protection gravel with a layer of lean concrete on top enough?

Hello King Song,

you yourself say these things are really heavy. You want to put in compacted gravel and lean concrete. So you almost already have your foundation. If you go below the frost line (here in Germany at least 40 cm (16 in)) you have (I assume the stones are 30 cm (12 in) deep, not 60) about 2.3 m³ (81 ft³) of excavation. If you do it properly (60 cm (24 in)) then you have 3.5 m³ (124 ft³). Don’t overcomplicate it. Put in 20 cm (8 in) of gravel, compact it well, and fill up with concrete to the top. Definitely some reinforcement. Then you have safety.

Steven

Steven schrieb:
(I think the blocks are 30cm (12 inches) deep, not 60) about 2.3 m³ (81 cubic feet) of excavation

But the concrete blocks are actually 60cm x 60cm (24 inches x 24 inches)... I hope that the 1.80m (5 ft 11 in) height will be enough to retain the slope with 1.60m (5 ft 3 in) behind it.