Excavation beside foundation/underpinning

One would just have to direct the frustration at the service provider. The neighbor relied on his words and competence. You only pointed it out. And in the end, the neighbor probably also prefers to have a short construction stop rather than having a fallen garage lying in his garden.

By the way. It turned out well here after all. Why doesn't anyone intervene immediately when the neighbor plans to build a pool? At the latest, when the excavator starts, I’m done with the fun.

By the way. This actually turned out quite smoothly here. Why doesn't anyone intervene immediately when the neighbor plans to build a pool? At the latest, when the excavator starts, that's where my patience ends.

Because with a professional company, one usually assumes that they will take the necessary measures to underpin, support, etc.
I can't always stand by the garden fence with the building inspectors when an excavator enters my neighbor's property, assuming that the excavator operator is about to cause serious trouble.

Because when dealing with a specialized company, one usually assumes that they take the appropriate measures to prevent, support, etc. I can't always stand by the garden fence with the building authority when an excavator drives onto my neighbor's property because I assume the excavator driver is about to do something really wrong.

Yes, one should assume that, unfortunately I have already been on far too many construction sites where that was not the case. Then grown men stand there and tell me they have been doing it like that for the last 25 years... and the same mistakes keep happening. Mostly, people try to save effort to carry out the job faster, easier, or more profitably.

Immediately involving the building authority is not necessary, but if something seems odd, question it critically and basically proceed as the original poster does here.

Alright, but the accusation here was that one should have acted almost clairvoyantly even before the work began, so that it wouldn't come to this in the first place. This is very difficult for a layperson, because they can usually only judge based on a gut feeling whether it fits or not... and you also don’t want to call the building inspection, scare the neighbor, and then the inspector says in the end "What do you want? It’s fine, isn’t it?" And you see, here a forum had to come first to get the idea to involve the building inspection or, if necessary, call the police. You just don’t want to mess things up with the neighbor, with whom you still have to get along for 20, 30, 40 years, and immediately cause trouble. And ultimately, you can’t blame the neighbor either. There are more than enough people who have no clue about statics, technology, etc., and actually believe that it will hold if the construction company says so.

Everything is fine, the OP handled it wonderfully and the neighbor can see that too, since he surely wouldn’t have wanted to pay for a sunken garage. All is well, no one is at fault – problem perfectly solved!