Cellar DPC underneath External wall DPC?

[Jeremy]

I'm renovating a semi-detached 1880s Victorian 2 storey home. It's got 9" solid double brick walls and no DPC installed. For obvious reasons there is dampness. So I'm planning to do a course around the outside walls (8x15x8m) of something I can inject like DryZone or an equivalent. Here's my question - there is a cellar underneath part of two of those three walls (it's in the corner, around 6x2.5m) with some dampness issues as well. I'm aware that the DPC should be above ground, so what do I do for brickwork that is underground in that cellar and suffering from rising damp? I'm assuming the DPC above will trap moisture in that wall, but should I do a second DPC below as well? I'm already planning on putting in a membrane, sand, and cement pad at 4" for the floor as well as some improved ventillation / dehumidifying.