I thought you might be interested in looking at When Will ArmA Terrain Builder Allow To Create Holes/Tunnels?.
https://forums.bohemia.net/forums/topic/221400-when-will-arma-terrain-builder-allow-to-create-holestunnels/?do=findComment&comment=3334992
× Pasted as rich text. Restore formatting
Only 75 emoji are allowed.
× Your link has been automatically embedded. Display as a link instead
× Your previous content has been restored. Clear editor
× You cannot paste images directly. Upload or insert images from URL.