Re: problems with water flowing under liner
As a rule, when you have water under a pool, you need to find a way to keep it drained, at least while you are working. There are various ways to do this, with different methods preferred in different areas of the country.
Once way is to place corrugated drains under the vermiculite, leading into a 'bucket drain' with a pump installed, and a discharge line and power line dug under the walls and away to the surface. Then, you can re-install the liner bottom and your new liner.
Obviously, if you don't have strong construction skills yourself this is work you'll probably want to hire this done. Just keep in mind they may do it differently where you live.
Ben
Re: problems with water flowing under liner
Welcome to the Forum!
You can certainly use hydraulic cement to patch small areas in the vermiculite, I've done it many times. (thanks or teaching me how to spell "hydraulic" ;) )
If this is a problem that only occurs when you have a period of heavy rain combined with spring snow melt off, it's probably 'surface water', as opposed to the level of the 'ground water' rising. If I'm correct, curtain drains would solve your problem, which would save you the trouble of installing a 'well point' and the collection network of corrugated pipe that Ben spoke of.
If you don't understand what the &&*%$ I'm talking about - feel free to ask for clarification - and if you'll give me a good idea of the topography of your yard (a couple pics would be worth a couple 1000 words), I'll do my best to help you design the curtain drain system. :)