h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

In February, we abandoned the 6-month long dig in a small N. Wales mineshaft, which was trying to find an way in to the nearby big shaft which linked to known (and only partially pushed) cave passage.

The main (big) shaft was covered over, and had been for some time - possibly since mining finished. In the '60s, access to the cave at the bottom was possible by another side-shaft which joined the main shaft ~20m down, but that side-shaft was comprehensively blocked, so we had worked on another side-shaft thought to be a potential easy way in to the big shaft. Some 20+m down, and ~40 tonnes of spoil later, the shaft died, so our attentions turned elsewhere.

However, there was still some residual enthusiasm, and the offer of a free 30 minutes of use of a JCB from the landowner resulted in the main shaft being uncapped at the start of last week.
We had expected to find a typical 1.5m diameter round shaft, but instead found a hole roughly 2.2m square. Given the shaft is over 50m deep, the landowner was naturally keen on having it made safe ASAP, so much work has been done since the opening.

The shaft top has now been cleaned down to bedrock, its sloping suface largely levelled, and four 3.5m long RSJs placed over the top to use as beams. By the end of saturday, we hope to have the beams concreted in at the ends, shuttering and a frame for an access hatch installed between them, and steel reinforcing laid in preparation for concreting.
Assuming we can get a ready-mix truck close enough to the entrance, the plan is to have about four cubic metres of concrete delivered and poured over everything, which should see the shaft secure for at least the next century, albeit at the cost of half the club finances. If we can't get a truck there, we may have to make the concrete with a couple of small mixers, which could be rather a long job.

Whatever the expense, in a few weeks we should be able to finally get into the cave passage at the bottom, though it now appears that the initial section 'may be little tight'.
However, with a drill and caps, or even our generator plus the hire of electric hammer, that should only be a temporary setback.

So 'Potholer' isn't just a randomly-chosen monicker.

Pattern-chaser

"Who cares, wins"

RSJs are now in their final positioning on levelled concrete blocks, with plywood shuttering fitted between them, shaft edges built up to shuttering level between beams, reinforcing steel cut and largely in position.

All that is now needed is the final shuttering for the area around the access hatch, some shuttering for the two edges along the outer beams, and placing of scaffolding bar stubs for the scaffolding frame over the access hatch, and *possibly* some more concreting around the beam ends to prevent sideways movement, and then we're ready for a concrete truck.

You crazy guy!

Hope it goes well.


az

I just *knew* this was Potholer's journal...when the title appeared on my PS

Yep, me too GB.
Goodluck Potholer!

Apparently, taking advantage of a spell of dry-enough weather, the concrete was delivered yesterday, with the truck being able to get right up to the shaft edge.
None of the shuttering collapsed (which was a bit of a concern of some people), and I assume the various blocking-off work around the lid was done.
By now the concrete should have started going off, and should be nicely strong in a wek or two, so exploration of the cave at the shaft bottom shouldn't be too far away.

I daren't ask...whether the concrete is "below" you or "above" you

It's a cap across a shaft top:
www.potholer.com/images/resources/parkshaft_open.jpg
and the concrete is cast around steel beams (shown with 3 of the 4 beams roughly in position:
www.potholer.com/images/resources/parkshaft_beams.jpg

Wood was placed between the beams, resting on the lower flanges, extra steel reinforcing was added between and over the baems, and then concrete poured over the whole thing.
A hole has been left in the centre for a [lockable] lid to allow access down the shaft.

http://www.potholer.com/images/resources/parkshaft_open.jpg

http://www.potholer.com/images/resources/parkshaft_beams.jpg

There, that's better.

az

Thanks, Az.

We had our first descent of the shaft today.
The top looks very secure - a big concrete slab about 12 inches thick, with lots of steel cast inside, and is fairly sheltered from the wind by the earth bank around it.

The descending began with a couple of gardening trips - someone slowly descending hanging on a rope with a hoe, knocking the obviously loose rocks on side-ledges down to the bottom. It sounded pretty scary from above when a whole load went down at once, but the shaft is now fairly safe. One small rock landed on a gardener's helmet - it was probably held in position by mud sticking it to the wall after rocks supporting it were knocked down, and just peeled off, but no daamge was done.

Tonight, 7 of us went down into the cave beyond. It starts with a flat-out low crawl ~45m down (~8m above the bottom), but the crawl is just wide enough at the shaft end to allow a crouch whilst getting on and off the rope.
A 2m climb down follows, then another 3m drop, with a small tube leading off to the top of another 2m drop - a little awkward, but passable with care and effort, and much feeling around with the feet to work out where the drop is. One more 6m drop (using a ladder, and wide, but a bit awkward leads to the horizontal cave passage which leads back under the [choked] shaft bottom and on to the digging site, which is a choked sandy crawl.
The cave is muddy but essentially dry (at least, at the moment), and there are a few nice small translucent formations.

Climbing out took a little time - the fastest ascents were 5 and 6 minutes, and the longest ~25, but that was from one of the senior members somewhat out of rope-climbing practice. I imagine everyone's speeds will increase if we start doing regular trips.

A bat was flitting around the top of the shaft as people were coming out - possibly it had discovered the hole in the weeks it was wide-open. Since the shaft now has a lid with a hole in (to access the lock), it should be able to get in and out freely if it wishes to move in, and there are several mine levels leading off from the shaft that should provide it with a good home if it needs one.

It's sometimes hard reading this stuff without going *gaaaaaaaa!* inside. Small dark damp places basically scare the f*ckety out of me.

Will you have more photos?

Not sure if a lone bat would be nesting there, but perhaps you only saw one of many. I had a rather full nest of them living in a brick over my balcony door last summer - ended up having to get my cats vaccinated for rabies (just in case) as they kept missing the nest opening and flying around my living room.


az

I know you do get huge colonies of bats in some caves (particularly in warmer countries), and they often nest in colonies in houses, but all the bats I have seen underground (maybe a couple of dozen in the UK and mainland Europe) have been on their own, even though I have sometimes seen significant amounts of droppings.
Maybe only the curious (or lazy) hang around when people come blundering noisily into their sleeping quarters?

Update:
The choked sandy crawl was at the end of a ~2m wide passage, probably quite deep, but choked up to within 0.5m of the roof with glacial infill (sand, clay, rocks). The passage turned righ and the roof dived down so we were digging down under the roof, and reagging the spoil back ~20m to where it could be stacked. A few weeks of digging made steady progress, though the time taken for everyone to exit the cave made it a bit impractical for evening trips.
Last weekend, 2 people brok through the crawl into a low space, with a boulder-choke visible ahead (and above).

Yesterday, 3 of us made a late-aftrenoon start, and began by clearing out most of the low muddy bedding plane that leads from the shaft to the cave proper (which made it a real pain to get in and out of). We then started clearing the end of crawl, which had been rather mouse-holed at the weeekend, and were joined by a 4th digger.
Much spoil was moved, and there is now a location from where it may be possible to safely prod the boulder-choke with a long pole - it seems a coffee-table sized block in the roof 1.5m above the floor is giving the most concern - if only someone had a licence for proper explosives...

Last week, after a brief hesitation to finish widening the entrance crawl from the shaft wall, the boulder roof at the end of the cave was lowered by judicious [and injudicious] prodding, broken up and hauled away down the passage to join the dump. Though we did miss the pub (again), we did end up able to get to where the loose boulders had been.

Essentially, the cave now ends with a crawl in a body-sized tube leading to a cross-rift where it is possible to stand. There isn't a way on ahead (unless it is down through floor-level debris), and the leftward branch of the rift quickly narrows off.
To the right, the larger and seemingly continuing rift is filled with mud and gravel to shoulder-height, where it seems at its visible widest, and where a large-ish rock prevents progress. The walls are of uncertain quality in places, since the erosion seems to have followed along multiple parallel joints, and there are some in-situ and nearly-in-situ slices that have dissolved away from the bedrock at various times.
The rock that needs to be moved is touching a flake of wall that is *probably* securly connected to Mother Earth, but at the moment, it isn't utterly clear just how securely.
Given the calibre of this potential loose cannon (~3m in its longest dimension), things have been put on hold until our resident digging expert has seen the situation and proffered his opinion.
It is possible the rift is wider still lower down, but that would still involve moving all the stuff that would have to be moved for a higher route through. There *is* a notciable draught, which is always a positive sign.

Still, we have many other irons in the fire, and a beer or two in the pub would probably be appreciated by most, so a brief change of battleground seems a good move all round.

After a couple of weeks of no real activity, some people went beck down to have a look at the dubious large rock.
From what i can remember of last night's telephone report, after some propping work with scaffolding, they squeezed past the large rock, and on to another crossing in the rift, from where a largely choked passage ~3m wide is descending at 45 degrees, with the draught blowing out of it.

It is apparently eminently diggable, though that seems likely to involve moving spoil from the new digging face back pastg the large rock, then through the low crawl at the end of the old digging face, then back along the passage, but it may be that it's possible to excavate and remove some passage just outbound of the old digging site to allow for temporary stacking. That would allow digging to proceed with a team of 3 or 4, alternating between moving stuff to temporary stacking and then moving from there right out to the final stacking space, though it would be nicer to get a decent-sized team of 6 or 7 down there and be able to move stuff straight from the new face to its final destination.

The *ideal* would be to be able to dig through the new passage and find stacking space on the other side, so the slope could be widened from the bottom upwards, though in cave passage so comprehensively filled in with debris from one or other ice age, maybe it's a bit optimistic to hope to find more space by digging downwards.