Oliver - 
I'd suggest the wooden box might be a secondary conduit/casing.  Although it would help to protect against digging, I'd suggest it would be more important protection if the ground is very stony or full of rubble debris - anything that might damage or crush your utility line even through the metal conduit.  Also, in the spirit of "they don't make things like they used to" the rigid line you describe just may be heavier gauge steel flexible electrical conduit.  Some gas lines, usually for in-house connections, have flexible steel lines as well.
Mike

Michael G. Angst
Senior Archaeologist
Archaeological Research Laboratory
University of Tennessee-Knoxville
Room 237,  Middlebrook Building
Knoxville, Tennessee  37996-0060
office:  (865) 946-1882; cell:  (865) 382-0931
fax:  (865) 946-1883
http://archaeology.as.utk.edu/ 


-----Original Message-----
From: HISTORICAL ARCHAEOLOGY [mailto:[log in to unmask]] On Behalf Of Oliver Mueller-Heubach
Sent: Monday, December 26, 2011 12:13 PM
To: [log in to unmask]
Subject: Re: Boxed or Encased Utility Lines?

Thanks! And Thanks to those who replied off-list! 
I've used the galvanized, flexi conduit before.. this line seems much more rigid (The rust left us wary to disturb it too much). Also, the spirals seem to have originally made for a relatively smooth surface.  I had assumed the spiraling was an alternate method of making the pipe (as opposed to rolling a narrow sheet into a tube, etc.). We only opened 3-6-foot sections, so the lack of joints could just be chance, but it would be neat if this was flexible material. It was pretty much arrow straight as we found it in the ground though..no waviness from being on a reel. Drainage in the area could be worse but I could certainly see this casing system proving troublesome in time.

So far possible purposes for the box include: 1. Electrical Insulation (I have been told of creosote covered/sealed examples 1918/19-possibly early 20s?), 2. Safeguarding against gardening/digging accidents, and 3. Temperature Insulation (probably not- assuming it is electric or gas).   

Thanks again- 
Oliver