Note: To those who know how to do it stop reading now.
When working on a dig underwater you may need to move large blocks. Sometimes you can pull blocks out of the way by hand or even break them up with a hammer and chisels or a bar. Use of a cow’s tail to attach oneself to the dive line allows both hands to be used. Hand moving awkward boulders is greatly eased by inserting a small bolt anchor (such as the easily hand drilled 8 mm type (if the boulder is difficult to grip); attach a short sling to the bolt. If the boulder still cannot be moved by hand try clipping chain of old steel karabiners to the bolt then insert a crowbar down through them which can be used to lever against cracks in the floor, giving a mechanical advantage. It is generally best if bolts are inserted low down in the front face of the boulder to be moved; this helps the boulder ride over irregularities in the floor and also improves any mechanical advantage obtained from the karabiner and crowbar method. In some cases these approaches will not work so you need a more technical solution:
- Rock solvent (bang)
Banging is quick but charges can be a problem to place (on the rock) it can also cause the area being dug to become (much more) unstable and often results in a fine coating of silt in the vicinity, which reduces visibility whilst working subsequently. Co-operation from a properly licensed user is also necessary.
The other option is winching. This takes more time to set up but can be very effective. One of the best options for cost and size is a cable hand winch. These can produce up to 4000 kg of pull (if placed properly).
You have a few options for fixing the winch. The body end needs fixing to either a large natural feature or you can drill an eye bolt into the floor or wall – and preferably also use a back up belay to prevent the cable whipping if the main belay fails. This needs a deep fix to stop it pulling out. Fix the winch to this with either a sling or a rope of suitable strength. It is not wise to fix metal to metal as you may need to cut it free. In some situations it’s better to have the winch body attached directly to the boulder so that you are always near the boulder and can thus jiggle the leading edge up with a bar when it gets stuck. If the winch body is remote from the boulder you either have to keep going backwards & forwards with the bar to free the boulder or you then have to try and overcome the obstruction by applying greater winching forces – this is dangerous as it increases the likelihood of a component in the system failing. However, if there is any possibility of a taught cable physically preventing a retreat down the passage then it is better to remain on the entrance side of the complete system. )
The rock you plan to move requires assessing for a stable direction to move it (if possible). This can be an alcove near its pre winched position or you may need to move it further down the passage to a larger area. It is also useful to chisel a rough chamfer on the lower leading edge of the boulder to be moved, which helps it to ride more smoothly over irregularities in the floor. If a dig is near the surface you can even remove it from the cave. In some situations the desired route to drag the boulder is not straight; in these situations it may be helpful to arrange an intermediate belay (usually a bolt in the passage floor) with a snatch block connected. Also, try to re-arrange previously stacked boulders in such a way that there is a space ready to accommodate the boulder to be winched; this is generally easier if done ahead of actual winching rather than after it (when the winched boulder will be in the way and when winching efforts may also have reduced the visibility). It may be possible to fix a sling around the rock and secure this to the cable. If this is not possible to fit a sling then again it can be drilled and an ring hanger Again, the use of a secondary belay on the boulder, to prevent the cable whipping in a failure situation, is strongly advised. If an eye bolt is fitted you must again fit a link than can be cut. The safe working load of any bolts used should be at least double the force which can be applied by the winch. If necessary you can extend the wire with a length of wire or rope (of suitable strength) but bear in mind that introducing any component with elasticity (especially dynamic rope) will reduce the distance that the boulder can be dragged.
Once all is in place move to the operating bit of the winch and start to take up the slack the non wire links ropes and slings will stretch). It takes some time before you start applying enough force to the rock to feel it start moving. Problems can be encountered if the passage you are winching the rock over is silt over laying rock or uneven this can hamper the rocks progress by sticking it will also cause an increase in silt and reduce the visibility (if you had any to start with).
You may need to use a bar to easy the rock’s progress. This should not be done with the hauling cable under tension. Once the rock is under tension from the cable it may suddenly break free causing the cable to fly about the passage. When you return to the digging area make sure nothing has become unstable.
Once the rock is free and moved out of the way you can if necessary repeat the exercise or if the winch is not needed then it can be taken home dried and given a very light oiling with a biodegradable oil.
Words of caution
- Check the winch over (visual inspection) for any cable chinks or damage to the mechanism before using it.
- When the cable is under stress it is possible for it to fail. The pent up energy will be dissipated by the cable flying down the passage. This can cause serious damage to anyone in its path.
- In small passages you should never place yourself between the rock and winch as the rock may move and block your exit from the sump.
- In small passages the cable pulling the rock could when under tension also block the way out.
- Always have a link at either end that can be cut (never metal to metal).
Thanks to John Cordingley for advice.