earth launched buried orion

I know this isnt original so if you have any references to a study
similar to it, please let me know.

Dig a vertical hole several thousand feet deep in a high mountain.
Put a nuke at the bottom and your Orion vehicle atop it. The hole is
evacuated. As the Orion ejects nukes, it rises. Finally, it ejects
the last few and instead of using the plasma to push it, it uses the
soft x-rays heating the ablation shield because the x-rays go much
faster than the plasma. This allows a fast closing shield to close
behind it so the bomb debris cannot escape. Such fast closing valves
were used on horizontal Line of Sight UGTs to allow x-rays and gammas
to reach experiments but to stop debris. I believe they were
explosively driven steel and concrete, not sure though.