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.
- Only place bolts where natural protection is not possible, so please
don't bolt natural-pro climbs or crack lines.
- Ensure the bolts you place are safe and installed in accordance with
the manufacturers instructions.
- It is generally permissible replace a damaged or insecure bolt by
installing a replacement in or about the same location.
- 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:
 | Sheer 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:
 | The force at the inner end of the shaft decreases if the shaft
length is increased. |
| Load is disbursed over a greater area as the shaft diameter is
increased. |
| The force at the edge of the rock increases as the point of
attachment extends away from that edge, just like a lever. |
|
| Tensile 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. |
| Torsion 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.
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:
| The 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. |
| Rated hangers or ringbolts are cheap and plentiful and more suited
to the task. In addition Chain is harder to clip. |
| Environmentally, chain is far more conspicuous than hangers or
ringbolts. |
| While 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.). |
| if 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:
| The plain bolt hanger is permanently attached to a bolt. Where a nut
is used, make sure it is secure. |
| Removable 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.
| Many of these bolts are home-made with no quality control. |
| The 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. |
| Without special equipment, it can be extremely difficult
to achieve optimum bonding between the shatft and the rock as a result
of poor glue distribution. |
| When 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. |
