The front porch on my 33-year old house is a concrete slab, 24′ wide, 10′ deep and 3″ thick.  My front yard slopes down and away from the house, and therefore the slab is at grade on the back left corner, but the front and right side are supported on a brick/block wall about 20″ high.  Over time, the slab and supporting wall have settled–about 1″ on either side and 2-1/2″ in the center, with hairline cracks running front to back.  The surface is otherwise OK.   I haven’t noted any settling in the past 3-4 years.   Question: can I add a new layer of concrete to restore the slab to its original level, and, if so, do I reinforce the new layer?  How do I bind it to the old slab?  Appreciate any/all suggestions.