Bolting

Adventure

 

Introduction

Bolts are used for protection and belay anchors on routes where other forms of protection are not possible.

Bolts are typically installed by fellow climbers, but that's no guarantee of a bolts durability or strength. Given it's not possible to confirm the strength of a bolt (anchor) by visual inspection alone, people should accept that they use bolts at their own risk of injury or death.

Ethics

Bolting is a contentious subject, however there are some generally accepted ethics that if followed reduce the chance of offending another climbers.

  1. Only place bolts where natural protection is not possible, so please don't bolt natural-pro climbs or crack lines.
  2. Ensure the bolts you place are safe and installed in accordance with the manufacturers instructions.
  3. It is generally permissible replace a damaged or insecure bolt by installing a replacement in or about the same location.
  4. Additional bolts (retro-bolting) or bolts in alternative locations  should only be installed after gaining permission from the person who first bolted the climb. Failure to gain consent has resulted in strong objections and in extreme cases bolts being removed or cut off.

Strength

There is an old saying , a chain is only as strong as it's weakest link and the bolts used in climbing are no exception. To understand strength we must first understand the forces that act on the anchor in different situations:
bulletSheer forces act at right angles (an angle of 90 degrees) to the axis of the shaft, for example if the bolt is installed horizontally and the the force is applied vertically.  The shaft functions like a lever, with the forces at the attachment apposed by equal and opposite forces within the rock. To counter these sheer forces use long large diameter bolts and position the point of attachment as close to the rock as possible because:
bulletThe force at the inner end of the shaft decreases if the shaft length is increased. 
bulletLoad is disbursed over a greater area as the shaft diameter is increased.
bulletThe force at the edge of the rock increases as the point of attachment extends away from that edge, just like a lever.
bulletTensile forces act to pull (or push) in the direction of the shaft axis. To reduce this type of force it is usually possible to position the bolt's shaft is at right angles to the expected load, resulting in the forces acting in sheer.
bulletTorsion forces act to twist or turn the shaft, however this type of force is not usually exerted on the bolt shaft.

A special note regarding bolts in Ignimbrite, which typically has a hard outer crust but a relatively soft inner core. Bolt should be as large and long as practical, to compensate for the weak inner rock core. 

Common Configurations

Bolts are typically comprised of two parts, the shaft which is secured into the rock and the attachment used to secure to climbing equipment. Below are some of the  bolt configurations commonly found in New Zealand.

BoltChains.jpg (20952 bytes) BoltHanger.jpg (15368 bytes) BoltRing.jpg (10155 bytes) U_Bolt_Problem.jpg (75006 bytes)
Chains Hanger Ring Bolt U Bolt

See Warning Below

Attachments

There are a number of different methods used to provide an attachment to the bolt: 

Chain - used in conjunction with a bolt (and washer), the links provide a convenient, low cost attachment point, however there are some issues to be considered:

bulletThe use of chain should not be encouraged over more modern alternatives. The use of chain at belays is acceptable, however most chain, particularly the galvanised general purpose type is only rated at around 8kN and has the potential for inconsistencies in its strength. 
bulletRated hangers or ringbolts are cheap and plentiful and more suited to the task. In addition Chain is harder to clip.
bulletEnvironmentally, chain is far more conspicuous than hangers or ringbolts. 
bulletWhile the use of chain at belays is more acceptable, there are better methods (such as two or three ringbolts or purpose built belay setups (like those manufactured by Fixe etc.). 
bulletif chain is being used then there must be washers BEHIND the chain in order to reduce the extraction force exerted by the action of the second link in the chain. an alternative to using washers behind the chain is to 'rout' a groove for the second link to sit in.

Hangers - typically take one of two forms, both of which are used in conjunction with bolts:

bulletThe plain bolt hanger is permanently attached to a bolt. Where a nut is used, make sure it is secure.
bulletRemovable hanger incorporate a key-hole slot to allow the hanger to be fitted by the leader and recovered by the second. In New Zealand the bolts used are normally 10mm or 12mm, so be sure to use the correct hanger size.

Note: Rope should not be threaded directly through a hanger, as the small radius edges may damage or even cut the rope.

Ring Bolts - combine a bolt shaft with a welded ring which is normally glued into place. This is an excellent system and two (or more) ring bolts provide an ideal belay anchor with large radius to protect the rope. an 

U  Bolts - a low cost approach, however BE WARNED there are some technical issues with this type of anchor that could compromise the anchors strength and long term durability.
bulletMany of these bolts are home-made with no quality control.
bulletThe holes must be drilled (within a few mm of)  the correct distance apart and the holes should be (within a few degrees of) parallel to each other. 
bulletWithout special equipment, it can be extremely difficult to achieve optimum bonding between the shatft and the rock as a result of poor glue distribution.
bulletWhen used on soft rock additional steps may need to be taken to ensure that the rock is not damages. As seen in the image above the U Bolt configuration can contribute to rock wear (caused by rope being pulled across the rock), damaging the outer crust and compromising the anchors.

Warning:  It is recommended that climbers use an alternative to U Bolts and be aware of the technical issues when using U Bolts.

Fastening

There are a number of different methods available for securing the shaft of the bolt into the hole and an even greater number of opinions as to which is best. The following is a summary of some of the most common methods:

Driven Bolts - considered by many climbers as inadequate, however the test of time would suggest otherwise. The method is typically only used on soft rocks like ignimbrite. Drill a hole (which is 1mm smaller in diameter than the bolt and  100mm to 150mm deep, then hammer in the bolt which has had a point ground on the end.

Expansion Bolts - are suitable for hard rocks. A hole of specified dimensions is drilled into the rock, the expansion bolt is inserted and the nut tightened to expand the bolt.

Glue - is applied into the hole of the specified size before the bolt shaft is inserted and rotated (to provide an even distribution of glue), displacing the glue providing a complete and even coating.

 

 

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Copyright Steven Riddell 1999, 2000, 2001, 2002 & 2003.