Hmm, i remember reading a mendip article on shaft building...
http://www.bec-cave.org.uk/index.php?option=com_content&view=article&id=545:caving-report-4&catid=58&Itemid=509&lang=en
I guess most people would say build it bigger than it needs to be.
Currently i can think of a few projects that are ongoing. But all are very different.
1. Renovation of a shaft dug in the early 2000's.
Being rebuilt from the bottom using glass fibre reinforced concrete and a mould, the mould is then removed when the concrete has set and then placed higher up the shaft. Typically 1m every two weeks.
2. A swallet hole being capped from the bottom up.
Plastic piping placed on removable wooden struts and shuttering, then sealed with expanding foam.
The expanding foam seals the bottom of the shuttering, allowing concrete to be backfilled outside of the pipe. This effectively seals the bottom of the cone, but with a hole in the base allows entry into the cave beneath. Good for conical swallets.
3. Scaffold and timbered shaft from the top-down- the buttered badgers and eldon pothole club are the specialists at this.
But the general principle is a large square shaft.
The scaffold is pinned to the walls by using drill holes and small metal rods which lock into the centre of the scaffold tube.
Timber is hammered in behind the horizontal scaffold bars, and the rings dropped down until there is no more timber.
(Perhaps theres a better way of describing this)
