Excavation for strip foundation too wide

Hello,

We would like to add an approximately 60 sqm extension to an existing residential building. It should be an age-appropriate single-story granny flat. The building report states that concrete can be poured directly against the earth, which the construction company had previously received from us. The construction company did not excavate for a strip foundation according to the report but instead dug a trench about 1.40 m wide for the foundation (40 cm + 8 cm perimeter insulation) and disposed of the earth without properly informing us beforehand. This not only causes us a lot of additional costs but also problems for further work and a lot of trouble. Because of this and other problems in advance, we have parted ways. Do you have any suggestions on how we should proceed with the strip foundation now? What makes more sense: to form all the formwork or to use formwork blocks? After the foundations are in place, should we refill the additional space with the remaining earth and compact it or use special backfill material and if so, which? What can we demand from the old construction company? Do you think it is possible to claim damages from them?

Thank you very much and best regards

Stefan

It is important with the foundations that the lateral support is ensured so that the foundation cannot break out (bearing capacity failure). I would fill it with gravel, compact it, and then excavate and concretize the "new" foundation trenches.... The gravel also drains rainwater better than clay soil (without knowing where you are building, I simply assume clay soil ;) It is of course more effort, but the damage has already been done. Unfortunately, I cannot tell you what and whether you can claim damages.

I would fill that with gravel, compact it, and then dig and concrete the "new" foundation trenches....

You want to dig a 50cm trench 80cm deep in gravel? I would like to see that.

You want to dig a 50cm trench 80cm deep in gravel? I would like to see that.

I just didn't find a nicer picture right now, but it should show what was wanted... Unfortunately no scale included, but that was for a frost skirt.

Here are 2 nicer pictures again... the 1st picture is for a larger foundation, picture 2 again for strips. In any case, it shows that you can also excavate in gravel and that with a pretty steep angle...

Yes, if it is well compacted, you can virtually excavate vertically. But it is of course very sensitive to loads or heavy rain. Therefore, it should be concreted as soon as possible and not only 3 days later.