They didn't have any clauses in their contract? They are at fault 100% no doubt and will loose in court for the pool repair, but what says they are responsible for your job? If they are responsible for installing a pool on uneven ground, then shouldn't you be responsible for installing a patio on uneven ground too? You say they should have had soil tests done, well how about you?
Say you build a retaining wall, holding back a large chunk of land, you finish you work and leave, all you were told to do is hold back the dirt. So you would expect, if your wall fails, to be responsible for everything on the job when you left the job site. Now what if someone builds a $1,000,000 home on the high side of the wall, your wall fails and ruins the home. Now who is responsible for the home? The builder of the retaining wall, or the builder of the home?
Where is that one tool, that I left... At the one job.... Or maybe the other? Where am I? Whose truck is this?