Hello G Jimenez:
You have to have space to get a jack in place and to get you in there to operate the jack. Right off, I can only think of 3 ways to do that; 1 raise the house up or 2 dig the dirt down, 3 take up some floor in trouble areas. Of course you don't want to dig down under the whole house; just pick out the worse places and work on them.
I shudder to think of the guys I've had working under houses; it sure isn't a comfortable or safe place to work.