I live in the country and have a pole barn with a cement floor. A critter of some sort has dug a burrow in the dirt under the outside of the barn and pulled out a couple of wheel barrows full of the gravel that supports the concrete floor. The entrance he dug out under the slab is at ground level and only about 12 inches wide. I am sure the critter is gone now but I have no idea of how to get all that gravel back under the concrete slab. I don't have any equipment like a backhoe, dozer, bobcat etc. Only hand emplements. Any suggestions will be greatly appreciated. Thanks. Trent.
Mix up a wet slurry of cement, sand and gravel and pour it in, then make some a little less wet and pack it in.
Unless you have concentrated loads there (commercial vehicle traffic, etc.), don't worry about it. Shovel what you can back in and be happy (assuming that you can plainly see the extent of the excavation).
If it's a concern, Try using some 2-3" pipe or flex tubing. Fill it with coarse sand or fine gravel. Slide the pipe into the end of the hole, then use a pole of slightly smaller diameter to push the material out as you slowly retract the pipe. Use the pole to compact the soil as you work your way out.