Since you have a concrete wall you re going to have to build out a new wall in front.
How to hang shelf on wall without support legs.
When you slide it over.
Then press your shelf against the wall for 30 seconds to fix it in place.
Install the top after leveling and screwing the horizontal brace to the wall place the particleboard or plywood on top the cabinets.
In this way the screw is firmly put into the wall and the shelf is then hung on the screw using various methods.
Remember that the top of the shelf will be above your marks.
You are essentially asking for a floating shelf albeit a really large one.
It should fit flush on top the cabinets.
Position the shelf on the wall.
Today for most of the wall mounting methods it is common to drill a hole in the wall where an anchor and a screw should be placed.
If possible attach adhesive strips to 2 adjacent sides of the shelf and hang it in a corner.
Then install anchors or drive the screws into the studs and hang the shelf.
Fit a floating shelf by pushing it onto the bracket instead.
How to add support brackets to existing countertops.
Most commercial shelving units come with premounted hanger brackets on the back of the frame this one uses a pair of keyhole brackets these are shaped so that the shelving unit can be slipped over the heads of support screws driven into the wall then locked into place by.
Mark inside the holes so you know exactly where to insert the screws.
Once you ve attached the adhesive strips remove the remaining strip liners and position your shelf along the wall.
Hold your shelf to the wall for 30 seconds.
The most difficult part of hanging such a shelving unit is getting the position of the hanger screws exactly correct.
Have someone help you hold the shelf against the wall.
In this case an 8 or 10 deep bracket is called for.
For example if your granite overhangs 12 inches past your 2 x 4 knee wall subtract 2 4 for the desired length of your support bracket.
A steel support structure is embedded inside the stud wall.
The size of your granite support legs and brackets will be based on your overhang.
You want something mounted on the wall that s heavy and going to need proper stud support but the stud isn t in the exact spot you need it.
A technique to borrow is how floating stairs are built.
Adjust the level until the bubble is centered and mark the keyhole locations on the wall.
Position the shelf brackets against the wall along the bottom of the shelf.
Use a standard level to make sure it s placed in a straight line then lightly mark the wall with a pencil on both ends.
With some setups the shelf rests on top of the brackets.
And why would it be really studs are basically every 16 inside the wall so the odds will not be in your favor to have one exactly where you need it.
Hang the shelf on the mounting brackets.