Richard,

I don't think you will find an archaeological manual that deals with this.  In my opinion, you should not look for one.  This is a very serious issue on which you should consult with a professional.  For example, you have left off of your list of risks hazardous like CO2/gas buildup and water accumulation.  Not only is special knowledge required to design and construct the reinforcing, but employees entering such a confined space are required to have special training. Also keep in mind that there are many, many factors that figure into designing a safety strategy, including sediment type, moisture, groundwater level, vibration from nearby roads, the weight of nearby structures.  Many of these issues are not self-evident to someone that lacks training. As conditions often vary, there isn't one standard plan. 

A man just died today in our region, trying to fix a well:
http://www.chicagotribune.com/news/local/ct-met-dry-ice-death-20130510,0,6601881.story
A non-archaeological example where they were using the dry ice to improve the porosity of the well (I think). While this seems a silly example, I have seen groundwater contamination strong enough it would foul the atmosphere and cause a person to loose consciousness in a confined excavation exactly like this case, which would require the rest of the crew to conduct an extraction.  That guy's buddy wasn't prepared to be able to extract him and he died.

Some technical literature is published in the United States through OSHA (as you probably know, Australia, Canada, and the EU have their government safety organizations with online information), but you should really consult with a construction engineer who knows the laws and best practices, or perhaps a first responder that has special training.  These sites list the government publications:
http://www.osha.gov/SLTC/trenchingexcavation/
http://www.osha.gov/doc/outreachtraining/htmlfiles/excavate.html
http://www.osha.gov/doc/outreachtraining/htmlfiles/cspace.html

Cheers,
Tim Scarlett


On May 9, 2013, at 9:40 PM, Richard Wright wrote:

> The dangers for archaeologists excavating old wells in superficial deposits are self-evident.
> 
> Two fundamental methods of preventing the dangers of collapse are (1) shoring, or (2) creating a safety zone by progressively excavating away the soil around the well as the excavation of the contents proceeds.
> 
> Can anyone point me to publications that discuss these dangers and how they can be prevented - preferably with illustrations.
> 
> Richard Wright