Fire Safety System Suffocates 20 On Nuclear Sub ..?
Break out a section of floor where it is sunken and find out what has happened underneath. The concrete may be suspended quite happily over a large void or it may just have settled into a small one and be resting on the ground again. either way you really need to know. Having determined the true problem you can set about putting it right. Hire a demolition hammer for a day and break back the sunken concrete to the good stuff. If you want a pretty finish use a disc cutter to trim the edges straight as well. Dig back under the existing slab a way and try to find the edges of the damp proof membrane. Fill the hole to the underside of the existing slab and compact it as well as you can using at least a sledge hammer. Lay heavy duty polythene in the bottom of your hole to overlap the existing membrane as much as possible - 150mm is ok. Buy a length of expansion joint from a builders yard - it looks like foam rubber sheeting about 150mm deep and comes in rolls. (If in doubt ask the shop owner and tell him/her what it's for, they'll know immediately what you need.) Place this all around the edges of the area to be repaired and fix into place either using a couple of blobs of mastic or even just leaning some stone against it until you pour the concrete when you should remove the stones and let the concrete do the job. Pour new concrete to fill the hole.
Do it yourself you can rent trenchers at HD or Lowes to go under sidewalks just push a pipe on the end of a hose with water runing through it. if you have to go under a wide driveway just use longer pipe.Or if you don't want to mess with it pick up some day laborers and give them each a shovel.Its not rocket science.
