Hello,
due to poor workmanship, we now have a 60 cm (24 inches) deep hole in the garden for a 6x3x2.5 m (20x10x8 feet) SwimSpa. The original plan called for 20 cm (8 inches) of gravel plus a 20 cm (8 inches) concrete base slab. Unfortunately, we now have a major problem. The pit can no longer be accessed by heavy machinery because of the actions of the previous landscaping contractor. This makes it difficult to deposit 8 cubic meters of gravel into the pit. Since the concrete base must be flush with the ground, 0.4 m (16 inches) of gravel would need to be installed. This would have to be done by wheelbarrow over a 30-meter (98 feet) access path with a slope.
For this reason, the current landscaping contractor has suggested pouring a 60 cm (24 inches) concrete base slab. They say the pipe from the pump to the pit can simply be laid that way. Attached is a photo of the pit. The garden soil consists entirely of limestone with soil classification 5. For this reason, the garden area was filled with 30 cm (12 inches) of topsoil. Along the long edge of the pit there is also a drainage pipe just above it. According to the construction survey, the soil has low permeability, kf ≤ 10^-4 m/s. The soil there is approximately class 3 to 5 — medium dense, dry to damp.
In the lower right corner, a layer of clay has appeared. I believe it is clay because on about 1 square meter, digging with a shovel is almost impossible — the soil sticks to the shovel and cannot simply be scraped off. However, my suspicion is that due to heavy rainfall, water collected in that corner over the last two weeks. Since the surrounding ground is mostly rock, it likely pooled there. I don’t know what this means in terms of construction.
The only access is on the right (visible in the photo where the fence panel is missing). For any other access, a crane would be necessary to lift materials over the house, which is about 50 meters (164 feet) for the crane’s reach, and there is no suitable crane setup area.
Of course, everything is somewhat possible... but my question is: is it really feasible to have a concrete base slab without gravel underneath in this situation? What would be a compromise—would 20 cm (8 inches) of gravel and 40 cm (16 inches) of concrete slab be acceptable? If so, should the gravel be compacted in layers or just the base once and then the 20 cm placed all at once? [Then the gravel could be delivered, and we would spread it ourselves by wheelbarrow over three days.]
We are really desperate. The reasons for this will be settled by our lawyer with the former landscaping contractor if needed, but the lawyer can only settle financial disputes. They can’t handle the practical work.
Best regards and Merry Christmas 🙂
due to poor workmanship, we now have a 60 cm (24 inches) deep hole in the garden for a 6x3x2.5 m (20x10x8 feet) SwimSpa. The original plan called for 20 cm (8 inches) of gravel plus a 20 cm (8 inches) concrete base slab. Unfortunately, we now have a major problem. The pit can no longer be accessed by heavy machinery because of the actions of the previous landscaping contractor. This makes it difficult to deposit 8 cubic meters of gravel into the pit. Since the concrete base must be flush with the ground, 0.4 m (16 inches) of gravel would need to be installed. This would have to be done by wheelbarrow over a 30-meter (98 feet) access path with a slope.
For this reason, the current landscaping contractor has suggested pouring a 60 cm (24 inches) concrete base slab. They say the pipe from the pump to the pit can simply be laid that way. Attached is a photo of the pit. The garden soil consists entirely of limestone with soil classification 5. For this reason, the garden area was filled with 30 cm (12 inches) of topsoil. Along the long edge of the pit there is also a drainage pipe just above it. According to the construction survey, the soil has low permeability, kf ≤ 10^-4 m/s. The soil there is approximately class 3 to 5 — medium dense, dry to damp.
In the lower right corner, a layer of clay has appeared. I believe it is clay because on about 1 square meter, digging with a shovel is almost impossible — the soil sticks to the shovel and cannot simply be scraped off. However, my suspicion is that due to heavy rainfall, water collected in that corner over the last two weeks. Since the surrounding ground is mostly rock, it likely pooled there. I don’t know what this means in terms of construction.
The only access is on the right (visible in the photo where the fence panel is missing). For any other access, a crane would be necessary to lift materials over the house, which is about 50 meters (164 feet) for the crane’s reach, and there is no suitable crane setup area.
Of course, everything is somewhat possible... but my question is: is it really feasible to have a concrete base slab without gravel underneath in this situation? What would be a compromise—would 20 cm (8 inches) of gravel and 40 cm (16 inches) of concrete slab be acceptable? If so, should the gravel be compacted in layers or just the base once and then the 20 cm placed all at once? [Then the gravel could be delivered, and we would spread it ourselves by wheelbarrow over three days.]
We are really desperate. The reasons for this will be settled by our lawyer with the former landscaping contractor if needed, but the lawyer can only settle financial disputes. They can’t handle the practical work.
Best regards and Merry Christmas 🙂
W
wiltshire25 Dec 2025 17:088 cubic meters of gravel roughly weigh 14 to 15 metric tons. If you can use a compact tracked dumper to transport it to the installation site, that would be about 40 trips back and forth. Although this seems inconvenient, covering a one-way distance of around 50 meters (165 feet) is quite manageable for two people in a single day, even if you’re not a professional and one person loads the dumper with a mini excavator.
There’s no reason to despair or to change the planned construction because of this.
There’s no reason to despair or to change the planned construction because of this.
Bernd001 schrieb:
Thanks... the thing is, the landscaping contractor just doesn’t see it that way... “back in the day” you would simply look for someone else... nowadays that’s more difficult. “We’re happy to help. Dump the gravel here for me, leave your dumper there, and come back the day after—that way it’ll be done by then!
Of course, you can always deviate from your original plan. But the risk is entirely on you (or does the new contractor sign off that it’s safe? If they take liability, then follow their instructions.)
W
wiltshire25 Dec 2025 23:34Bernd001 schrieb:
So the big question is whether he is right with "we don’t need gravel underneath." He is not, if the soil is cohesive, because it is not only about frost protection but also drainage to prevent waterlogging and a capillary-breaking effect. The durability of the concrete slab is definitely worse without the frost protection layer.
Who made which mistake is irrelevant; what matters is how to achieve a good solution.
Bernd001 schrieb:
“Back in the day” you would simply look for someone else… nowadays that’s more difficult. Finding someone new may be hard – that may be true. But it is definitely better than being talked into some kind of botched job.
Similar topics