Thermal expansion is also a well known property and something that is dealt with in buildings and structures all the time. It would be a challenge, I agree, but I don't think it will be an intractable one.
There's 2-3 orders of magnitude difference in the scale of ordinary structures and the scale of the hyperloop. There may be a solution, but so far AFAICT no one has actually come up with even a plausible-sounding story. You can't simply say, well, we've solved the problem for small structures so surely we'll be able to solve it for larger ones.
