Wolfy,
It sounds like you are trying to dig wet clay, if so you are just spinning your wheels, clay is weird material to work with, when wet it will be very slick to walk or drive on, but very sticky lumpy to dig in.
If it is wet, just sit back take a breath and let it dry, then you can use a sharp edged flat tipped shovel to shave the clay a little at a time working from the low side toward the high side, a good garden till to help break it up will also help.
Putting anything between the clay and pool bottom will certainly help, (as long as the clay is LEVEL first), and yes use concrete pavers under the support legs, and make sure they are level with the surface the bottom of the liner will be sitting on.
Here is the result of not placing your pool on solid level ground without pavers under the support legs!
http://www.troublefreepool.com/pool-sinking-on-filter-side-t45679.html
Trust us when we tell you to take the time and effort to do it right the first time.
We are having to build up our yard for our pool, but we have lots of heavy equipment to work with and even then so far we have over a month of time invested in the project and still not done.
Good luck