This is a very challenging potential installation and there could be several potential approaches. For the shotcrete to bond to the existing concrete, the existing surface should be properly prepared, removing any unsound concrete, then roughened and cleaned to allow for a good bonding interface. You mentioned using rock anchors or bolts. These should be installed before any shotcrete.
For each 6 in. (152 mm) layer, a layer of welded wire reinforcement or structural fibers should be used. These, in conjunction with the rock bolts, should ensure the stability of each layer of the shotcrete from falling.
The surface reinforcement should not be installed before most of the area is within 6 to 8 in. (152 to 203 mm) of the final surface.
There is currently similar thicknesses being placed on the East Side Access in New York City to build back the overbreak for the initial tunneling to the “A-line” or profile that was intended for the mining.