So here we go.
I am going to play arround with tunnelsystems.
i curved arround but i got is that: http://www.filefront.com/17861577/dm_tunneltest.map/
EDIT: Link changed by ReD
its a simple tunnelpart, with textures caulk and anything what is need to play it.
but the ground and walls are not massive.
Please have a look on it