Ingleton Bolt Seminar.
It is generally agreed amongst all cavers that the “best” anchors to use for a belay (be it SRT or ladders) are naturals such as threads or flakes which have the least impact on the cave environment and on the whole are the most reliable. However, in order to gain a “safe hang” and avoid rope rub or an impossibly wet descent a compromise is reached by the use of bolts which when well placed and properly maintained give a safe and discreet means of descent.
The problems arise when permanent fixtures such as the ubiquitous MB self drilling rock anchor, begins to fail (eg. Rowten Pot incident), usually by misuse by a large number of parties. This led to the all too familiar condition of “bolt rash” where certain groups rebolted popular routes not trusting the myriad of other bolts placed by other mistrusting cavers.
It is not realistic to simply rebolt a route when the present bolts are unsafe as all bolts require sound rock if they are to be safe. Clearly this is a finite resource at pitch heads and they will not last forever. It is easy for people to think that permanent bolts are the answer merely because they last up to 7 or 8 times as long as a standard M8, however the conclusions of the seminar were that as permanent bolts cannot be removed once installed bolt—rash will still occur but only at a later date. To avoid this a “semi permanent” design was agreed upon which could not be removed without considerable effort and forethought. This would be done when the safety of the bolt became questionable and a new semi-permanent bolt placed in the existing hole. Before arriving at this conclusion several other options were considered and the various advantages and disadvantages of bolts discussed.
Potentially available rock anchors.
M8 self drilling rock anchor: (see diagram) Widespread use, some in lethal state. 5 years expected life, failure by enlargement of threads due to gritty bolt insertion and rusting.
M8(Austenitic stainless steel)
Not available presently but possible that they could be manufactured en masse. No rusting problems, 15 years expected life, failure by thread enlargement but bolt harder than hanger.
L8 (Martensitic stainless steel):
Also not presently available with no rusting problems. 10 years expected life. Failure by thread enlargement.
Expanding bolt fixings: eg. Rawl bolt(M12E):
Not used presently due to theft problems but bolts placed am removed at every trip in Pant Mawr causing enlarged holes. Failure by shearing of bolt at root of thread. Lifetime of hole is around 1O0 annual replacements.
Petzl P38 hanger: see diagram:
has a permanent hanger and is totally made of stainless steel, eliminating
rust. Expected lifetime 30 years. Mode of failure is
likely to be rotation of the bolt in the hole causing a reduction in
compressive grip between bolt and limestone.
No proper feasibility studies of the removal of these bolts is known of but drilling out the locking pin seems the only possibility. This would be extremely difficult and time consuming.
Safety Harness Eyebolt: (Hilti/Rawlbolt)
This bolt will not fail under any of the loads generated by SRT practice and conforms to BS5845. It is reported that the resin in the Rawlplug version will decay by water damage. These require a 19mm hole! for insertion and has an expected life of about 100 years (this is the theoretical lifetime)
Stud Anchors (often used by window cleaners):
Having the best strength to weight ratio this was considered but rejected as there is no removable version. Expected life 20 years.
Chemically Fixed Eyebolts:
These can divided into two types: Petzl P40 and a DMM design currently used on some BMC owned crags.
Petzl P40: (see diagram) A galvanised eyebolt with an extremely high strength (over 4 tonnes). Rejected as it is not available in stainless steel and removal would be virtually impossible.
DMM stainless resin hanger: (see diagram) Removable, very strong (c.2 tonnes), cheap (consists of a single 8mm stainless bar). Placed in an 18mm hole 50mm deep. Removal by drilling out exposed resin and twisting out leaving an undamaged hole ready for- bolt replacement. This DMM design was decided upon to replace bolts on heavily used routes such as Gaping Gill, Ireby Fell Cavern and Lancaster Hole. Some have already been placed for testing purposes in Yordas Pot, Kingsdale proving to be very strong. Plans for rebolting are being coordinated through the NCA. It is not proposed to rebolt every cave with the new design which would be too expensive and time consuming, only the popular caves. In caves such as Crescent or Quaking Pot the stainless variety of MS may be appropriate as it would receive so little use.
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