South Bristol Speleological Society

The spring of 2004 saw a lot of rain and it was about this time that the fate of the dig again changed dramatically. The East Twin Brook when low flowed quite happily into the cave. The majority of the water would disappear in the sink at the bottom of the first chamber and very rarely was there sufficient flow to pass through the Squeeze and down the bottom of the cave. Despite the councils previous efforts, following heavy rain and the majority East Twin Brook would still flow past the entrance and would continue down the valley towards the road.

The council had decided this was a situation they were unhappy about and decided to take action to prevent any water from reaching the road. A digger was brought in and an even larger earth bank was constructed outside the entrance to direct the full flow of the brook into the cave. This had catastrophic results inside.

Since the majority of the cave had been dug dry over the years, mud and rock spoil could be left at a relatively steep angle and would remain stable. Since it was not necessary, or practical to completely excavate the lower chamber, only sufficient spoil had been removed at ceiling level to allow diggers to pass and buckets to travel the monorail.

With the full flow of the East Twin Brook in spate, several things now happened. Large amounts of mud, rocks and bio matter were now washed down the East Twin valley and into the cave (where previously the majority had been washed past). Just inside the entrance, close to the foot of Dam 1, the earth bank was now being seriously undermined and washed further into the cave. The flow of water was now washing rocks from the first and second chamber into and past the squeeze, almost blocking it each week. Most significantly a huge amount of spoil and rocks from higher in the cave had now reached the bottom which was frequently sumped for days at a time.

Not only was progressed stopped as we could no longer enter the third chamber without spending all night trying to dig out the sumped squeeze, but also several months, even years of digging had been washed back down in a matter of weeks.

We knew that unless we could stabilise the top of the cave we would stand no chance at addressing the problems lower down. We also knew that unless we did something significant, it would not be long before the entire third chamber in filled, Spar Pot and any hope of pushing the dig further would be lost.

Reluctantly, we took the decision to build some cemented stone walls at the top of the third chamber in the hope of trapping the majority of the rocks and bio matter (rows of bags had simply been washed away by the force of the water). Late February 2004 saw the start of the walling. Two walls (Dams 5 & 6) were built in the hope that we could keep them emptying them and keep the fresh in wash at bay.

However this was only addressing one of the problems; in the mean time water was continuing to wash down the third chamber and late March 2004 we made another slightly alarming discovery. “Son of Kevin”, the large boulder ½ way down the main chamber had now become unstable. It had been resting on a bank of rock and mud, lashed in situ with some thin cable. Recent rain had now washed away the bank of mud and it was now hanging on the cable freely swinging. In this condition it was not safe to venture past it.

In June we decided to see what could be done with this ½ ton boulder. We ventured down the cave with some steel cable, a cable winch and a 1 tonne bag (the type which builder’s sand is delivered in). With the aid of a scaffold bar we managed to swing the boulder around enough to wrap the bag around it. We attached to the cable to the 4 lifting lugs and started to winch. The plan was to lift up and over the edge of the scaffolding gantry where it could be safely lodged.

The lift started well and with constant prying from underneath the bolder was moving up nicely. It was moving up until the carabiner hit the scaffolding. Despite all the levering, prying, man handling we could muster, although the carabiner seemed to clear the bar it would go any higher. Meanwhile the time the cable was still being winched yet the boulder was not going up. The inevitable happened, the cable snapped. Luckily, very luckily, the bag the boulder was in snagged and came to rest on one of the bolts from a scaffold clamp.

There followed some frantic re-lashing of the cable onto the bag to take the weight off the bar and to get it ‘safe’ again (luckily no one was struck by the recoiling cable either). For some reason we though it might be a good idea to try again, although there was some doubt as to why the result might be any different. This time we connected the cable, made sure the boulder was free to travel up and this time everyone below the winch went and hid in Spar Pot. Somewhat unsurprisingly the result was much the same, the cable did again snap and this time there was nothing to stop “Son of Kevin” falling all the way. Nothing except the bottom of the scaffold gantry which we had though was well secured. Obviously when it was installed 15-20 years previously catching falling ½ ton boulders wasn’t in the requirements and the whole 30 foot gantry shifted 6 inches down the cave. This was a problem as the mud and rocks that it had been supporting were now unsupported and liable to collapse. After going do to see where “Son of Kevin” had landed and to stomp it into a safe position, it was at this point we decided to retreat.

Walling and tidying up continued through the rest of 2004 in an attempt to stabilise the top of the cave. A lot of the rocks which had washed down the second chamber were moved back up, the ‘steps’ above the Squeeze were re-built and the Squeeze was kept open. Polyethylene was put on place at the edge of the main stream way in the cave to try to prevent further spoil being washed down. A small section of chain link fencing was also used to retain rocks in the first chamber while allowing water to drain through (Dam 4).

With the top of the cave a little more stable it was time to address the third chamber which had continued to deteriorate. The plan was to build a series of vertical dams to trap rocks behind and to absorb the force of the falling water. With the unstable nature of the lower parts of the chamber, we had no option but to start at the top and work down.

With no stable base to build off, cemented rock walls would not have been safe enough, so after much discussion it was agreed the only option was to install more scaffolding and wood dams. The Axbridge Caving Group very kindly agreed to let us use their battery drill to drill the holes needed to bolt brackets to the walls of the chamber.

In January 2005 work started on Dam 8 just below the old winch dam. Scaffolding was arranged such that railway sleeper sized pieced of wood could be installed vertically and then as the bottom of the dam was dug out they could be knocked down into position and the process repeated. February saw the completion of Dam 9, built in the same way.

In April 2005 we suffered another set back. Torrential rain had overcome Dam 6, the lower wall in the second chamber and despite the polyethylene being in place a huge pile of spoil had been washed down the cave, into and though the Squeeze and down the third chamber.

After a week of re-opening the Squeeze we found that the newly installed dams 8 & 9 had done their job. We had only half back filled them to allow them to trap future in wash. However they were completely full already and the remainder had obviously gone down the bottom.

One thing the torrential rain did do was to open up a small sink just behind Dam 5. May saw several evenings digging away to see if this went anywhere. As expected however it only disappeared down the edge of the chamber and into the rock debris on the floor. We spent the reminder of the summer fixing the walls.

After the summer holidays we returned to investigate the situation below Spar Pot. A large amount of debris had been washed down and the old Spar Pot dam itself had started to undermine. Although September saw some remedial efforts to stabilise the bottom of the gantry we realised we needed to do something pretty significant. It had been the best part of 18 months since we had been able to think about the lower part of the cave and it made depressing viewing. The chamber had slumped past Better than Sex which was no where to be seen. The monorail had been forced to the ceiling by the weight of the slumped debris. The old Spar Pot dam was slumping out from underneath and was becoming very unstable. The spoil which was had been held back by the gantry had slumped away and the gantry was now just in the way. Hope was fading.

Return of the Jedi

It was about this time that the club received an email from an old digging master, Phil Hodgkins, who Jane’s account shows was digging in East Twin over 26 years previously in 1979. Hearing our plight, Phil very generously offered to make a donation to the club to help purchase some scaffolding which would be needed to make any serious attempt on rescuing the lower parts of the cave. The club diggers also agreed to have a whip round to match Phil’s donation for the purchase of a generator and a drill.

Throughout October and November 2005 a significant amount of damage was done to the lower part of the third chamber. Evidence that the chamber sumped all the way up to the level of Spar Pot was regularly seen. The old Spar Pot dam became a hanging bridge of bags and old scaffolding with nothing supporting it underneath. Warnings were posted on UK caving sites. The whole chamber had now slumped back up to “Burt Inlet”.

Despite this we kept the Squeeze open and we were planning with a renewed sense of hope. Phil’s donation had re-kindled our enthusiasm and we were determined to keep the cave open.

With the rate at which the cave was backfilling and the sense that we were fighting a losing battle we considered a number of desperate options. We even spent an evening surveying the Squeeze to see if we could blast through another opening to come through just above the winch. This would have given us the option of extending the monorail past the winch and into the second chamber. As it turned out we would have had to tunnel through nearly 2m of solid rock. We also considered building a large wall just in front of the Squeeze to allow the rest of the cave to back fill against it, only letting water though.

We settled for a less dramatic approach which would maintain as much of the character of the cave as possible. It had always been our intention that once digging efforts were over and a reasonable objective had been achieved we would tidy up the cave and hide as much of the evidence of digging as possible (although that will be a mammoth undertaking in itself).

In November Ian Mildon managed to get hold of some cable tray, one piece of which we immediately put to good use in the entrance where the water enters the first chamber and made a retaining wall (Dam 2) to stop the whole area from being washed away.

In January the drill and generator were purchased and on 23rd February 2006 a somewhat bemused driver delivered the scaffolding to the lay by in Burrington Coombe. As it turned out, the 10 x 6m (21ft) lengths we’d purchase were just about as long a length as you can through the entrance crawl, another foot or so and we’d have had real problems!!

Of course getting the poles into the cave turned out to be the easy part. We knew that getting them through the Squeeze was going to be the real challenge. The plan was to knock a second hole to the right of the Squeeze to pass the poles though.

The spring and early summer of 2006 saw a frenzy of activity. The ‘pole hole’ was knocked though the Squeeze and with a small amount of excavation each side sufficient clearance was achieved to pass 7 of the 10 poles through leaving 3 for walls in the upper chambers.

With a 50m and a 30m extension cable we could get 240v down to Spar Pot. This enabled us to drill 6” deep pockets into the solid rock and locate horizontal bars exactly where we wanted them. We fixed vertical bracing bars to these which and fixed cable tray shuttering behind. The cable tray is able to retain the mud and rocks while allowing the water to drain though.

We continued to work our way down with the new Spar Pot dam (Dam 10) by digging down and fitting progressively lower horizontal bars, shuttering and backfilling through the gaps. Despite having 2 drills working simultaneously it was still slow work (it didn’t help that most of the diggers had given birth to a new generation of future diggers that year). Also during the summer or 2006 we dug out the sink at the bottom of the first chamber to take as much water as possible and built a small retaining wall to stop it slumping. The intention was to open this out to take as much of the water as possible.

By the autumn the risk of more bio matter in the top of the cave had been mitigated by a scaffold and cable try dam just below where the water enters the first chamber. This inclined 3ft dam (Dam 3) lets all the water though and traps everything else.

Work continued on the Spar Pot dam for the remainder of 2006 and into the spring of 2007, and by March we had gone as far down as was reasonable. Work then began on the next dam (Dam 11) which has now also been completed.

Currently we are in good shape; we have space behind the new Spar Pot dam and behind Dam 11 to dump spoil without the need to take it all the way to the top of the cave. We’re also using pairs of scaffolding poles as slides to raise buckets with a rope and pulley. The old scaffold gantry is being removed as we dig it out and we are making use of the old scaffolding where it is safe to do so.

With the current rates of progress we hope to get back down to Better Then Sex within a few months and hopefully then beyond. We have yet to find the final resting place of “Son of Kevin” but it can’t be much further!!

The old dam just below the winch (Dam 7) is in serious need of renovation, it’s not entirely obvious what is keeping that in place at the moment but apart from that it looks like we should be able to survive this winter without anything like as much damage as there has been in previous years.

There have been many postings on the UK Caving Forum regarding this cave and I don’t propose to answer all the critics. I would agree the bags and the metal work in the cave do look unsightly, I would say though without them the cave would have filled in by now to a point where the Squeeze would remain impassable and Spar Pot would have been all but inaccessible.

Before Phil’s donation it was looking like we were losing hope, now we are set to recover much of ground we lost when the stream was redirected. I’d like to thanks all those who have given their support over the years and I hope in the future I or my successor will be able to make the long awaited announcement that it actually goes somewhere..!!

BoB Clay
October 2007