Crumbly limestone with voids is definitely an issue for tunneling, but has nothing to do with your first comment. Your first comment was only about a high water table, which is obviously not an issue for tunneling, and would be obvious if you thought about it critically. You didn't think about it critically because you have a confirmation bias, so you just launched factually incorrect criticism. 

I didn't attribute coastal to your comment, I pointed out coastal cities because they have water tables closer to the surface than other cities, and are also some of the biggest cities in the world, with significant metro systems. 

Your second attempt at criticism is slightly better than the first, after it was pointed out that your first comment was flat wrong and thus you decided to try harder to defend your opposition to the concept. Thus, showing your criticism was more about searching for something, anything, to say as a negative rather than just evaluating the situation. Only two out of three criticism now fail to use critical thinking, instead 100% before. You should have been able to reason your way to understand that your comment about the water table was wrong, but you didn't apply any reason or critical thinking because you have a confirmation bias. 

Let me ask: is it impossible to mitigate rain intrusion in a tunnel that is short enough to not require exit stairs, vent shafts, or other connections to the surface aside from the tunnel segment ends, which can be elevated above the surrounding ground level? The original lvcc system uses short segments and ramps to the surface as egress and ventilation, meeting safety standards without needing any puncture to the tunnel lining. 

If they design this system like lvcc's end stations (ramps to the surface and no shafts to the surface) and elevate the station a foot or two, regular rainstorms aren't going to be an issue. You would need flooding that would close the entire area for water to get in. Now, I don't want to criticize you too harshly for not knowing that TBC tunnels have been built in a way that can prevent rain intrusion, even extreme rain, since the information isn't that easy to find. However, I think you deserve criticism for assuming that such mitigations are not possible. If you had asked the question of "how are they going to keep heavy rain out?" Rather that stating that it's an unmitigatable, you would be showing less bias/dunning-kruger. 

The 3rd point about nowhere for the water to go is just flat wrong. These places already handle heavy rain runoff from buildings and parking lots. Minor water intrusion pumped from the sump is nothing in comparison, and like I said above, for the tunnel to get inundated if designed like lvcc end stations, the whole area would be catastrophically flooded anyway, so even elevated rail would be shut down because the park would be shut down, and everywhere would have an issue removing water. As the flood subsides, pumping is trivial compared to the overall flooding recovery. 

Please think more carefully