Price compression with lava

Good morning,
unfortunately, I couldn't find the civil engineering section, I hope this fits here.

We want to install a garage in October; for this, a ground slab needs to be poured along with a corresponding foundation involving excavation 0.5m deep and placing and compacting gravel 0.3m thick. The area is 7x9m. Additionally, all excavation material from the house should be transported away.

Today, a local civil engineer was here. Costs per truckload (10 tons), 180 euros. Additionally, about 150 euros for the entire excavation. Bringing in lava and compacting costs 35 euros per m3. All prices excluding VAT.

The transport price is okay. However, I find the price for bringing in the lava at 35 euros really high.

Can a general statement be made here? We asked for a fixed price, but that wasn't possible. He cannot estimate the amount of soil lying on our meadow. But he is the expert. I obviously cannot do this. I simply calculated the volume of the slab and then multiplied it by the loosening factor of 1.3. Can't he do that?

So:
35 euros for lava including compacting okay?
Can one demand a fixed price? Is it common that civil engineers do not agree to that?

Thanks and regards
Stephan

morning,

for the soil replacement, as for all other civil engineering materials, what the region provides is usually used, meaning what the local dealers have in stock. As far as I know, lava gravel is basically approved for foundation subbase, but the stuff should be quality-controlled (this guarantees, among other things, the correct sieve curve, i.e., grain distribution) and the grain size should be right. For creating a frost-free subbase, a grain size of 0/32 mm is usually taken and recommended – what does your civil engineer want to use? It would also be interesting to inquire about the water retention capacity of the "lava." After all, you don’t want to create an underground lake but to drain the water cleanly and quickly into deeper layers, i.e., it should be solid, dense rock, definitely not granulate.

Frost-free is also the keyword for the depth of the soil replacement: 50 cm seems too shallow to me, because despite the harshest climate warming, the so-called frost penetration depth in Germany is still between 60 cm (north) and 120 cm. If the rare effort of soil replacement is carried out, sufficient depth would be helpful. Unless at 50 cm depth you already have a frost-proof layer (what does the soil report say?).

If you want to reduce the price, you can switch from natural material to concrete recycling in the grain size 0/32 mm. Generally, this should be cheaper material-wise than natural stone. Your price apparently includes labor, so the material costs are only partial. You could possibly reduce this share to about 5 - 10 € per ton (that’s what RCL costs here gross). Possibly get an alternative offer prepared.

Regards
Allrounder