Cliefden Caves: Repair of the Donkey Tail

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GARRY K SMITH NHVSS | The ‘Donkey Tail’ is a stalactite which formed in a passage initially above the water table and was then submerged in a pool of calcite-saturated water for a long time.

As very slow CO2 degassing and water evaporation has occurred, over time the calcite coming out of solution has been deposited as spar crystals. These crystals have completely covered this and other stalactites as well as the surrounding walls of the passage.

At some point after the crystals had been deposited there would have been a flood event which deposited a very fine film of orange-brown clay over all the speleothems in the passage.

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I am assuming this particular decoration is named ‘Donkey Tail’ because it looks hairy with all the needle-like spar crystals and has a lump on the end just as some breeds of donkey have on their tail.

Background

During a visit to Malongulli Cave (CL 69) in 2005, I noticed that the decoration known as the ‘Donkey Tail’ had been broken — cause unknown — though suspected to have been accidentally knocked by a caver getting too close. I am told that the breakage had occurred between 2000 and 2005.

The broken piece lay on the floor for a number of years before Denis Marsh retrieved it for safe keeping in early 2011. At the end of the 29th ASF Biennial Conference in January 2013, held at Galong in NSW, a sizeable contingent of attendees travelled to Cliefden Caves for a week of post-conference caving.

This was the perfect time to undertake the repair, so I prearranged with Denis to do so. Here is the extract from my trip report (Smith 2013) describing when and how the repair was undertaken.

Tuesday 15th January 2013

Today we set out for Malongulli to repair the broken ‘Donkey Tail’. Those in the group were Denis Marsh (T/L) (OSS), Harry Burkitt (HSC & NHVSS), Tom Porritt (VSA), Lance Hoey (CEGSA), Greg Thomas (WASG) and myself.

The cave ladder was tied off and lowered down. Denis and I carried two heavy packs laden with the broken stalactite, tripod, glue, battery drill, drill bits, spare batteries, cloth, camera and flashes.

We entered at 9.45am and soon made a chain of people to pass the heavy packs through the cave to the repair site. The broken stalactite was photographed at various stages during the repair and on completion.

There were a number of difficulties which had to be overcome; the most annoying was the constant drip of water which came from the end of the section of broken stalactite still attached to the ceiling.

This meant that while I was pre-drilling the hole for the pin overhead, a cloth had to be held on the stalactite next to the rotating drill to soak up the water. This situation posed a danger should the cloth catch on the rotating drill bit and wrap itself around it, potentially with dire consequences for the remaining part of the stalactite attached to the roof of the passage.

Then there was a small 6 mm long straw, which had started to grow on one side of the stalactite and prevented the correct alignment and fitting of the broken piece. This calcite deposit was ground away with a small grinding wheel inserted in the battery drill.

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Keeping the grinding process cool was not a problem as the water continued to flow from the end of the broken stalactite. While I was undertaking these operations, Denis took plenty of photos with my camera for the records.

Eventually I was ready for the glueing process, having made a final check to ensure that everything fitted and that the camera tripod was able to support the broken piece while the glue set. At this point, Denis took the others for a tour of the rest of the cave and that gave me more time to take stock of the last stage of the glueing operation.

As mentioned in Smith (2010), there is not much time between mixing the high strength polyester resin (rock bolting glue)1 and when it goes hard, so once I started, I had to work quickly.

Anyway, the operation went smoothly and the glue set hard. I then set about photographing the final result of the repairs. I had almost finished packing up when the others could be heard returning.

Perfect timing. The others could help carry the equipment back out of the cave.

It was a job well worth doing and it gave me great satisfaction to see the elegant speleothem back together. We placed a row of rocks on the floor as a visual barrier so that cavers would be more aware of the delicate formation above. We emerged from the cave at 1.30pm in time for Greg to depart for Canberra and the rest of the group to return for lunch back at the hut.

Equipment used

Ground sheet, packing foam, DSI chemical anchor glue, battery drills and extra batteries, good quality HSS drill bits, small rotary grinding bit, 316 grade stainless steel 6 mm threaded bar, surgical gloves, glue mixing spatula and mixing tin, cloth rags and camera tripod.

A camera with slave flashes was also handy to document the repair. 316 stainless steel threaded rod was used as this grade of stainless is salt water resistant and as such will not corrode in cave conditions.

Equipment selection and methodology

Surgical gloves were used to reduce contamination of the speleothem from skin contact and perspiration. The DSL chemical anchor tube containing the glue is the type used in coal mining for rock bolting and is manufactured by Dywidag-Systems International Pty Ltd.

It is a high strength polyester resin, which sets quickly in water and sticks to almost anything. The composition varies with the grade of DSL anchor tube and generally fits into the range quoted above.

The DSL chemical anchors used for this repair contain two colours (green and brown) of glue and a white internal hardener tube, all contained in the one plastic tube. When the green and white agents are mixed together they set in about two minutes, while the brown and white set in about ten. Obviously, the cave temperature will have some bearing on setting times.

High speed steel (HSS) metal cutting drill bits were used at low speed to drill a hole in the end of the mating ends of the speleothems so that the threaded stainless steel rod could be glued inside. The drilling speed was slow to reduce heat generation in the speleothems and reduce wear on the drill bit cutting edge.

The hammer (percussion) setting on the battery drilling machine was not used to reduce vibration of the fragile speleothem segments. Cooling water can be used if the speleothem or drill bit starts to warm up.

Repair sequence

To allow the two faces to sit together as they were when first broken, a small calcite deposit which had grown on the stalactite still attached to the roof was ground away. A small hole was then drilled in the centre of the mating faces, along the axis of the speleothems to accept the threaded rod, which was to act as a strengthening pin.

Once both mating pieces were drilled, the pin was inserted without glue to check that the adjoining outer surfaces of the speleothem could be aligned exactly.

The holes had been enlarged to allow room for the pin to float more freely, so as to align the outer surfaces. When all mating parts could be easily aligned, the glueing operation commenced.

The appropriate quantity of glue was squeezed out of the DSL chemical anchor tube on to the bottom of an empty fruit tin for mixing with a spatula.

On this occasion the slower setting chemical anchor glue was mixed up and smeared on the pin and inserted into the hole. A piece of soft foam was placed on the top of the tripod — the camera attachment pad — and the tripod was wound up to take the weight of the speleothem while the glue set. This allowed a better glueing operation as holding the pieces steady while the glue sets is very difficult.

References

Smith, Garry K. 2010 Repairing the Rootsicle in Wildmans Cave, Wombeyan, NSW. Caves Australia 181: 18-20 Smith, Garry K. 2013 29th ASF Post Conference Trip to Cliefden Caves,
11th -16th January 2013. Newcaves Chronicles 40: 9-14.


  1. For those interested, the composition of the Dywidag-Systems International Pty Limited (DSI) rock bolting glue is between 6.9–11.9% polyester resin, 78–87% calcium carbonate and 4.4%-6.0% water.