Gabion with backfill (compacted) as garage driveway

Hello and thank you very much for reading

We are currently in the middle of building a house. The basement has now been constructed (Souterrain), and starting the week after next, backfilling will begin. In the process, we forgot an important detail in the planning, and I am currently looking for a good "rescue."

Specifically, we are building on a hillside plot (with a fantastic view). The plot slopes down towards the valley from the street at the front side. The street itself has an incline, so we are building higher than the neighbors next to us. For various reasons, this results in a boundary construction. While the neighbor's garage driveway slopes down about 100cm from the street, our driveway rises by 50cm from the street.

This means that our garage driveway at the boundary is up to 150cm higher than that of our neighbor. Therefore, we need to build a retaining wall directly on the boundary. The neighbor already has a wall at the boundary, but of course it only reaches the height of his driveway (our plot was previously lower). The building permit for our wall is approved, but the exact type of wall has not yet been determined.

The retaining wall has a total length of 6 meters, it starts at the same height as the neighbor's wall and then rises slightly in height, while his slopes downward:
-----------------------------------
(higher) Street (lower)
-----------------------------------
same height | same height
..................... | v
50cm higher | 100 cm lower
-----------------|--------------
Our house | Neighbor's house
..................... ^Retaining wall

The probably best solution would be to simply set concrete L-shaped blocks. However, here we have a problem with delivery times. The L-blocks take about 3 weeks – unfortunately, we don't have that much time. I have not yet found a concrete plant that can deliver from stock.

Another idea is the use of gabions (metal baskets filled with stones). Personally, we would also like this option better visually. If we could manage with 30cm wide gabions, the somewhat narrower driveway to the double garage would also not be a problem.

Does anyone have experience with gabions as a retaining wall?

Since our driveway is directly behind, the soil would have to be compacted behind the gabions. I have already googled this. Some write that this would be sheer madness because the gabions could bulge when compacting and become a hazard. Others write that layer-by-layer compaction of the soil (while simultaneously filling the gabions with stones) is no problem.

What is correct? Can 30cm wide gabions be used as a retaining wall and the front yard/driveway compacted behind them without the gabions bulging? Do the gabions need a concrete foundation, possibly even additionally concrete-embedded metal pipes, or is a 40cm gravel bed sufficient (I have also found contradictory statements about this)? Is there a type of stone that is particularly suitable for filling in such an application?

I look forward to any tips. Please do not ask why we are only doing this now. The wall actually slipped through the planning. It was included in the building permit, but we did not request it from any of the trades, and it only became clear just before Christmas that it actually needs to be built in January. We have an architect, but only for the house and not yet for the outdoor facilities. Therefore (and because of holidays/vacation) I am asking the experts here.

Best regards and many thanks from
tabaluga

Straight away: Gabions are purely decorative/visual elements that serve as wind and noise barriers and, in hydraulic engineering areas, also as protection against sand winds, etc.; they were never intended as retaining walls.

The structural requirements alone for a freestanding 150 cm high, 30 cm wide gabion are already considerable. A foundation must be built with appropriate drainage as needed so that the gabions stand firm and stable, cannot sink at a corner/side, etc.; for every running meter, 2 supports must be concreted in the middle (e.g. steel pipes or steel posts) that should be about 10 cm lower than the height of the gabion so that they are not visible later, because gabions over 100 cm high are not stable by themselves and there is a risk of tipping over.
The steel mesh bodies (usually delivered as a kit) must be filled by hand; subsequent compacting is not possible as they are simply not designed for this, and the connectors between the side walls are also not designed for it.

The filled soil would push the gabions away. Moreover, as I understand it, you won’t see any of it anyway because your property lies higher than that of your neighbors, right? Regarding gabions, I would otherwise recommend that you call the company Unger and Bultmann in Ahrensburg; they can advise you very well and maybe have a solution, but keep in mind that gabions usually have about a 1-week delivery time plus assembly; filling them is quite hard labor, not to mention the foundation (curing time).

Angle retaining walls (L-walls) are the best choice. There are many manufacturers in your area, Siemsen in Schwarzenbek, Rekers Betonwerk in Spelle, Westerwelle in Herford, Seling Beton in Melle, possibly also Hacon in Rellingen, and depending on how flexible the guys are, Berding Beton.

For the load case (car traffic 5 kN/m²), the walls are usually kept in stock; at least that’s how I know it from Siemsen and Westerwelle, unless you want beveled edges at the top, which are always custom-made.

I would love to sell you some (I work in building materials trade) but unfortunately I can’t get to that area *g*

Hello bauXpert

and thank you very much for your detailed feedback. Last week I immediately wrote quite a few emails to the companies and also spoke with Unger/Bultmann on the phone.

Meanwhile, a good solution is emerging (thanks to you as well). I am happy to write down our now probably final version here again for future readers with a similar problem:

- Angle supports are actually much easier to get than my civil engineer wanted me to believe. He spoke of 2-3 weeks delivery time. In the end, I could have had the supports from about 40% of the dealers within a week. However, delivery costs must not be underestimated (we needed 6 meters at 80-150cm height and would have paid between €375 and €620 for freight) - certainly justified due to the tonnage of 4 tons, but still quite a hefty amount. Ultimately, we found what we were looking for locally at a building materials dealer who could get the supports from another dealer (50km away) and deliver them for €15 (we are located in southern Lower Saxony).

- Angle supports have the advantage that they have a standard static calculation and therefore no new structural calculations are needed. They are available in standard heights (130cm) and then higher/lower in 25cm increments. In width, there are 50cm and 100cm.

- We would have paid about €3000 for the entire wall (stepped design).

- Fa. Unger gave us great and committed advice: Gabions are also possible as retaining walls in these dimensions. However, it gets quite expensive. The gabions are probably then more than 1m deep. They are anchored with a geogrid that extends about 1-2 meters from the gabion into the ground. This gives them the necessary stability. However, since there is no standard structural calculation for this, the statistics must be calculated, which makes this version quite expensive and also time-consuming.

- After further research and as things stand now, we will execute another/third variant: We are using natural stone palisades set in concrete. The cost of this version is about 25% lower than that of the angle supports (including labor time), the color tone is selectable (there are sandstone colors, various grays and reds) and the appearance also pleases us significantly more than the bare concrete supports. Although we also found out with the angle supports that there is a dark concrete variant that would then look almost anthracite and thus much more modern. According to the landscaper, a wall height of over 150cm is also possible with the natural stones, and the steps can be finer due to the smaller width (20cm) of the stones.

Thank you again for the great help, which really brought us a good deal further, and I wish you a successful new year
tabaluga