Rigging in China
Rigging in China
by Rob Garrett, April 2001
(This is an article for the report on rigging techniques especially for China).
Rigging the caves and dolines of China proved to be very different to rigging caves back in Europe. It's not that European techniques wouldn't have worked but rather that much more efficient approaches were available for those that could take advantage of them. The basic techniques needed to take advantage of the available opportunities are summarized in three parts below.
Line of Descent
In Europe it is established wisdom to seek for free-hangs with good rock. When dealing with dolines well in excess of 100m deep this tends to lead to hangs of the order of 100m: great fun on the way down but very inefficient on the way up--especially for large groups or inexperienced prussikers.
A much more efficient approach is to choose the least steep approach route. This is likely to contain sloping ledges and lots of vegetation. Although daunting at first sight moving from tree to tree provides innumerable opportunities for rebelays and often the rope is only necessary as a safety/hand line. Such routes are seldom immediately obvious but have served local nitrate minors since long before SRT was invented and listening to the locals will usually reveal where such lines are best found.
There is still some danger from rock fall, especially on the frequent scree slopes so the most efficient way to get large groups up is to travel with small groups in close convoy, which is also much more sociable than conventional SRT.
Rigging from Naturals
Placing bolts by hand is tedious. Rock can sometimes be unreliable or unsuitable for bolts. In China there is an abundance of naturals just waiting to be taken advantage of. Not the traditional European naturals such as stalagmites and rock threads (although these do exist as well). These are real naturals such as trees, or at least tree stumps and saplings.
Although most of China's trees have been chopped down (as have most of Europe's) on the exposed crags and ledges of the dolines a few still remain. At the top of the doline a few sturdy looking fellows are still to be found and these make perfect anchor points and backups. For main hangs and rebelays it is usually necessary to use smaller trees but they still seem to be up to the job. For deviations, however, branches and saplings abound. These tend to be a bit less fixed than a good thread and it requires a little extra thought when placing deviations. Not only do you have to consider where the rope will want to pull the deviation crab but also where the deviation tape will subsequently bend its springy anchor point too!
When choosing your trees for rebelays I find the following guidelines helpful. For some reason the best positioned trees are always the dead ones. This is not a problem though for consider: dead trees used to be alive. When they were alive they would annually grow a heavy foliage and blossom. In the wet the additional weight of water and foliage would probably exceed the weight of your average caver. Therefore, the tree is capable of taking the weight of a caver. Conversely, a living tree in blossom could already be stressed to breaking point and the additional weight of a caver could just tip it (and the caver) over the edge. Of course, it is a realistic concern to ask what if a tree did try to fly while you were dangling below it. Obviously the bigger the tree the greater the shock load it would place on any other anchor points. The sensible conclusion is that the smaller the failing tree the better. Thus it is better to choose smaller trees as anchors, all other things being equal. Obviously there are other considerations when choosing which tree to belay off such as which one gives the best hang.
With deviations it is well known that they do not need to be as strong as rebelays because they will not receive as great a loading. Accidents have, however, been known to occur when deviations have fallen and this can be particularly scary for people below them. For this reason I favour minimalist rebelays (i.e. twigs and saplings). Nobody is going to be unduly scared by a twig floating past -- especially if they are wearing a helmet.
The theory of rigging with rub points was first explained to me one drunken night long ago around the Bull Pot Farm fire after a particularly memorable trip down Hangman's Hole. The basic principle to be exploited is that when a rope runs past a rub point the tension above the rub point is less than the tension below it. Thus, by deliberately inserting rub points into your rigging it is possible to reduce the loading on the main belay. In some cases, for example the penultimate pitch in Hangman's Hole this is seen as a worthwhile objective.
In China I made a logical extension to this theory and applied it most successfully when rigging Scree Sunday -- a 150m scree slope loosely consolidated by a veneer of calcite such that its slope in places well exceeds critical angle. However, the theory is also usefully applied when trying to reduce the loading on tree belays of dubious quality.
In the case of Scree Sunday the main anchor is not under any special doubt -- it's a car sized boulder perched quite happily on the apex of a scree ridge. The problem is that rub points are unavoidable and rebelays are not sensibly possible (any attempt to place a bolt will shatter the calcite coating and free the scree exposing it and the bolt to the normal laws of gravity). However, a rub point is also not desirable if it's going to be loaded for 150m of ascent and descent. Since the ascent and descent are unavoidable if exploration is to continue the only viable alternative is to somehow reduce the loading. Of course, this may be achieved by inserting a second rub point below the first. The sooner this second appears the sooner the loading on the first is reduced. This has not solved the problem, however, because there is now the new rub point to worry about. A third rub point takes care of this while further reducing the load on the first for an added bonus. Extending this approach in the obvious iterative manner will eventually bring you safely to the base of the pitch with as many rub points as you have imagination and opportunity to create. In the case of Scree Sunday a stubby boss permitted a rebelay for the final 10m hang which contained a single rub point at its head. This was the only one of the 30 rub points which actually damaged the rope necessitating a rope protector and that is because there was no opportunity for additional rub points below it so it had to endure a full loading every time.
It should be noted that sharp rub points are always undesirable as they only require a small loading force to cause catastrophic damage to the rope!
WARNING: The authors accept no liability for any accidents resulting from anyone trying to implement any of these techniques!