Hello Everyone, I'm new here.
During the last couple of years, a 'dip' has been gradually developing on my garage floor, at the front, on one side only, just under the door. As I drive in-and-out, the car wheels - front, then rear (only one side) - roll over it and this makes it worse, little-by-little. In the last couple of months, it has got worse now. The floor has a coloured, plastic-type coating, with - I'm sure - concrete underneath. The area from crack-to-crack, or dip-to-dip, is about 3ftx3ft (1m X 1m).
I am thinking of hiring a breaker (electric) and dig a square hole, then refill with hard core
and finally concrete. I would like to know
1. Is this the way or the best way to tackle the problem?
2. If so, how far should I dig down?
3. Do I just put hard core, or also some sand in between?. and finally
4. What kind of ready-mix should I select and how do I calculate the amount needed?

As the result of a repair, I am not worried about the aesthetic difference between a concrete repair patch and the cooloured plastic cover ofb the rest, as long as the floor is level and strong.

I thank anyone for the answers and if there is anything necessary that I have not mentioned, please tell me.
:)

You could also consider a floor jacker, they pump mud under high pressure under concrete and actually jack it up. Check the yellow pages for a concrete jacking or floor leveling company.

My first reaction would be to just live with it. Of course, I don't know how bad it is.

I suspect that the weak subgrade might cover a larger area than just where your car is applying pressure.

Your strategy for repair is sound. Once you open up the area in question, you will be able to probe around to determine if you need to expand your repair.

It would be best to excavate to undisturbed ground, and backfill with a good quality aggregate. Road mulch, (3/4 minus crushed rock) is designed to pack solidly. Use a vibrating compactor. In small areas, a "jumping jack' works well. If the underlying soil is soft, as it is where I live on a river estuary, you can strengthen it with rocks which you pound down into the soft subsoil with the jumping jack. Clean drain rock (1.5" or 2") works as well. You can tell it is getting stronger by how your compactor is behaving.

If you use road mulch, it needs moisture to compact. I can't help you with how much, as different kinds of rock behave differently. Crushed granite is the best of all, if available. Too much moisture and your compactor will bog down, too little and you won't get good compaction.

Work in 6" lifts when backfilling and compacting. Did I mention to use CRUSHED backfill? The sharp edges and flat planes lock together when it is compacted properly.