PS, I'm wondering if the lime is to be used only in the tunnels and voids above them, not in the central shaft, since a previous Update said

"The filling of the voids above the tunnels (not in Silbury 1) and the outer section of the tunnel will be filled using a pumpable chalk paste material".....

whereas the hill top void will be filled with [i]"a pumpable slurry chalk mix" - which sounds rather wetter to me.

I could be entirely wrong, but in a situation where such vital details are deliberately kept under wraps, speculation based upon crumbs is all the public is left with.