No clue why this is downvoted, these are valid concerns.

Measuring and avoiding ground settlement consumes an enormous amount of engineering and contracting resources in every urban tunneling job.

Flooding too can lead to work stoppages or long delays. You should have seen the Queens Bored Tunnels and Structures Project after Hurricane Sandy. It was pretty soupy.

Source: Was a tunnel boring engineer in NYC, where we had an abundant supply of both buildings and groundwater.

Any large project is likely to have difficulties of some sort that need to be taken into account to overcome: it's the nature of the beast. You're right, these are valid concerns. Asking the questions as your parent does implies that those at the Boring Company—while they may have not solved them in all cases—are not aware of them, especially as these aren't new problems. I speculate that the downvotes are a reflection that your parent isn't granting them this benefit of the doubt. One can infer from the FAQ that they are thinking of this in part from the R&D bullet point:

> Tunneling R&D. In the United States, there is virtually no investment in tunneling Research and Development (and in many other forms of construction). Thus, the construction industry is one of the only sectors in our economy that has not improved its productivity in the last 50 years.

An engineering study of ground subsidence and how to avoid it, vs "the building falling down" are two very different things.

No, it doesn't. If it did, buildings in NYC would be falling down left and right. Heck, I hear they even put them under entire bodies of water!

Yes, tunnels can flood, if they are below the water table. Good pumps can fix that problem. Again, the Chunnel being Exhibit A - it hasn't flooded, yet.

Isn't most of Manhattan ground solid rock? There are many other places where the ground it's just compressed dirt

Yes, but in those cases the tunnel structure itself ends up taking up load previously carried by the material that's removed. That is why the walls of the tunnel are shored up with reinforced concrete rings, which provide mechanical support AND keep out water. That's why we have tunnels that are bored only a few tens of feet in the mud under deep bodies of water, and yet don't collapse or flood.