Congratulations on your find !
I had a B. pascuorum colony that had set up home in some long mossy grass in my garden a year or two back.
I never saw them working on the nest dome, but over a few weeks it grew considerably - from half small tennis ball to half grapefruit.
I’m convinced that the work was all done from the inside of the dome.
They also made themselves a “landing cavern” in the moss close by; and I saw them trimming grass leaves that were in the way.
Yes, BBs seem to firm the soil in their entrance passageway, but I don’t know how, it might just be traffic compaction, like us humans wearing a path in the grass.
I hope this helps. Clive
Thanks for your comments and interesting observations of your pascuorum nest. Yes, I do feel very fortunate in finding it.
I found it fascinating to see a worker locating a hole in the ground just big enough for the bee plus pollen load to enter and then watch them emerge ‘empty’ sometime later!
Some years back I saw some B. lapidarius workers going into a crack in a lawn - there was no sign of a proper entrance.
Enterprising things bees !