In my poly tunnel they used to take up residence and as you say, they turn the soil to mush. When they become a problem it is best to get rid of them.
What I do is get some Borax ( readily available on ebay for a fiver) and some caster sugar as ants love sugar.
Mix just one or two spoonfuls of Borax and the sugar together with a tiny bit of water .... make a paste. Spread it on a bit of cardboard and put it down near the entrance to the nest, in fact if you have loads, put a number of mixes down .. the ants disappear and thats it. No fuss, no mess and no ants.