Considine's Cave Dig (South End)

Present depth as of 15th June 2020 = 20.5 metres or 67.25 feet.
Total Man-Hours = 1499
Preamble

To fully understand the scale and complexity of this dig, reference should first be made to the 'Considines Cave North End' description on the 'Projects' Page (Click Here). A complete history of the North End dig is available in the 'Logs' commencing July 25th 2016 and concluding 30th December 2017.

Considines Drone 1.JPG

North up. A drones eye view of the relocated infrastructure, the "winch shed" aligned with the rift directly beneath.

Introduction

 

The excavation of the Northern half of the rift has all but concluded. Upon reaching a final depth of some 25.5 metres a small east trending down slope passage developed, here the diverted northern stream rejoined the shaft. After some four metres the passage and stream entered a parallel, immature joint, here the stream turned toward the south; hence the decision to dig out the previously shored up southern rift. Outstanding tasks in the northern half of the rift remain its survey, remove the infrastructure and secure the entrance on conclusion of the entire project. 

The northern and southern halves of the rift yet remain separated by the timber shoring, which was installed from -2m to -14m; down through large, loose boulders and irregular occurrences of clay deposits. As the floor of the southern side is lowered the shoring is being removed and brought to surface. This procedure allows access to remain via the original fixed ladderway, then across a two metre long “Gantry”, down a second two metre ladder into, and onto the southern rift floor surface, which is at present at a depth of around seven metres below the platform. 

Of particular note are the feature comparisons of either half of the rift, from an equal depth. Both east and west walls of the northern rift, at around -7m, begin to subtly undulate, mirror like, whereas both southern rift walls remain vertical, at an average of one metre apart. Below -7m both northern walls inexorably narrow to, and below -14m; this is the location of “The Plank”; the narrowest point reached is at the “The Pinch” at a depth of -22m.

From the nature of the exposed southern rift walls, cautious estimates suggest some twenty four cubic metres of spoil may need removal to reach “The Plank” at a depth of -14m; assuming the rift walls remain vertical and the same width apart. Research suggests weights of wet and dry clays as averaging 1.4 metric tonnes per cubic metre and the unidentified sandstones and hard shale like boulders average between 1.4 to 2 metric tonnes per cubic metre; therefore conservative estimates suggest around thirty four tonnes will require lifting to surface.
 

current 1.JPG

View north of new layout, winch shed to the rear, hauling area to the foreground.

current 5.JPG

View looking South at -6.5 metres, showing radius of the rift and stepped method of fill removal.

current 6.JPG

View looking North from the South side of the shoring, originally installed when the north rift was excavated. Beyond the shoring the shaft descends to the Plank at -14 metres, thence to -26.5 metres.

current 7.JPG

View looking up the hauling area showing shoring and shaft collar above, the pipework  conveys a significant volume of the southern stream to the North shaft.

Phases

Phase 1.   Preparation of the surrounding area and installation of a working platform,

tripod and associated infrastructure. Total man-hours  72 from 14 visits.

Phase 2.    Removal of infill from the North End plus fitting heavy timber shoring at the South down to -14.5 metres. Final depth reached -26.5 metres at which point it became too tight. Total man-hours 1061 from 151 visits.

Phase 3.   Relocate surface infrastructure to allow removal of infill from the South End with the eventual result being the entire rift will be emptied. Man-hours to date at the South End (25/10/18) 497 from 87 visits.

TB digging whilst a large Boulder in the net is winched to the surface

PC empties one of the kibbles into the barrow, this one a single boulder

Showing the size of the shaft and the enormous task of emptying it 

Pegasus supports the “Guillotine” 

As spoil was regularly removed from the southern half of the rift a narrow cleft was noted gradually increasing in width as depth was achieved. Minor concern was expressed as the cleft appeared to deepen, and widen, yet it offered promise of passage perhaps, at some lower point, large enough to enter. At -11m this cleft had become 0.4m wide, creating a large protrusion, in appearance to the bow of a ship. Unfortunately it appeared to be free hanging. Under normal cave conditions this formation would be passed without giving it a second glance, but, as digging continues downward this lump will remain as a threat to the poor sod working below, certainly for the immediate future, with no place to escape its mass.

Following extensive examination the majority of this lump of rock, aptly named “The Guillotine”, did, in fact, appear solid and secure at a point some two metres from its free hanging base; it was these lower two metres that focused the gravest concern accentuated by the eroded horizontal bedding and how far through this bedding water had penetrated. The chosen solution was to support it directly beneath itself with an RSJ, secured to the east and west walls.

The thin profile of the bottom of the “Guillotine” meant that if it fell away its weight, and pressure, on any support would be magnified by its very narrow lower edge. So a 200mm x 100mm “H” section steel RSJ was obtained, even so another section of RSJ was added to the area directly beneath the point of contact to spread the load further. These two pieces were welded together for increased strength, the whole prefabricated item finished with a protective coat of paint.

Options to secure the RSJ to the rift walls were explored, including creating recesses in both rift walls into which the ends of the RSJ could be inserted to rest upon. The final decision was to prepare and drill heavy sections of angle iron secured in place to the walls with multiple 16mm galvanised steel pins. These brackets secured in place as a letter “L”, the RSJ when place in position was wedged up against the inside of the “L” to avoid it tilting forward, should, and if, pressure become applied. To reduce the chance of the RSJ tipping away from its vertical position a brace was fabricated which secured it to the west wall and by bolts to the top of the RSJ; rotation through pressure now significantly reduced.
 

Angle-iron support brackets pinned to the wall with 16mm bolts and re-bar pins to stop lateral movement of the RSJ

The RSJ with the added welded section in it's final position, under the "Guillotine" 

The brace to reduce the chance of the RSJ tipping away from its vertical position

With the “Guillotine” now supported attention turned to avoiding it falling out eastwards, or sideways. Two lateral stemples were prepared, one located near the top of the “Guillotine” at around -11m, the other near its bottom, some 0.4m above, and inline with the RSJ.

It should and indeed must be clearly understood, all this preventative work and extensive precautions are just that, optimistic precautions; no guarantee can be applied or assumed, or is inferred that the “Guillotine” won’t actually move. To descend below the level of the “Guillotine” you do so entirely at your own risk. 
 

The West end of the RSJ before the brace was fitted

Job done and now Safe (hopefully) to work below

 
Horizontal Image of the Site at minus 14 metres

 

Calculated floor areas at the minus 14 metre point are:- 

North End (shown above the timber shoring on the survey) 1.35 square metres.

South End (shown below the timber shoring on the survey) 6.79 squre metres.

That is Five times the amount of spoil being removed at the South end compared with the North.

This photograph, taken by Roger Day from minus 16 metres shows the enormity of the task involved in emptying out this impressive shaft. The patterns at the top are caused by light penetrating through the different configurations of pallets used to construct the working platform. The builders ladder positioned at the bottom of the fixed ladder is a temporary measure until the "Platform" is installed at minus 14.25 metres.

The Platform (Minus 14.25 metres)

The idea of the platform emerged after addressing two particular issues; 1) The need to maintain access along the “Plank” into the northern shaft, and 2) Have a secure frame from which to suspend the next fixed ladder. During its conception other factors were examined not least construct a small level floor on the ladder frame where a brief respite from climbing could be had, whilst enjoying the view from this forthcoming loft eyrie.

With the aid of a laser level PC drilling the pilot holes for the 16mm bolts

 

The platform frame is simple, consisting of two galvanized scaffold poles, from their ends 16mm galvanized bolts locate into holes drilled into the living rock; securely tightened. At right angles to the poles, two lengths of angle iron secure the timber flooring to the scaffold tubes. On this platform floor rests the “Plank”; six inches wide it passes through the cleft and is secured to the original bracket fixed at the northern shaft edge. 

The finished platform with the first section of ladder in place giving you access to the level floor, presently at minus 16 metres

Phase 4. With all the heavy timber shoring removed and the floor level below the access point into the North shaft via "The Plank", work can now proceed to remove the final 10 metres to bring us level with the lowest point reached in the North shaft and hopefully access into open cave. Man-hours to date at the South End (08/07/19) 1039 from 180 visits.

And the spoil heap just gets bigger and BIGGER

A view of the access ladder from minus 18.7 metres

Calculated floor area that requires removal in the South End at minus 18.1 metres is 7.47sq metres

At Easter time 2019, Martel & Basher Baines, members of the Bradford Pothole Club were in County Clare for their annual all things speleo and drinking expedition. (more drink than speleo if I recall). They had visited the Considine's dig the year before and expressed their interest in producing a video to be shown at the B.P.C.'s annual get together. The result of their efforts can be seen here .

  Watch Video  

 
As of 31st December 2019 we have spent a total of 1386 man hours, lifted 5567 loads from 241 visits at the South Shaft!
2020

Could'nt Organise Visits Involving Digging due to Covid 19. The surveys below show the floor area just prior to the three months period of lockdown.

After nearly four months self isolating the site could do with a haircut

The following photos were taken by Jim Warny on a visit to give a safety check of the infrastructure and prepare the site for a renewal of digging.

Looking down the hauling way from surface. The pipe carries surface water from the Southern end into the far North shaft.

Taken looking up from the present floor level at minus 21.5m showing the platform at minus 14.5m

Taken from the access ladder at minus 5m. The grey triangle is the platform installed at minus 14 metres to offset the ladder into a wider area of the shaft.

Taken looking directly up the access ladder-way from the present floor level of minus 21.5m

As of 15th June 2020 we have spent a total of 1499 man hours, lifted 5817 loads from 265 visits at the South Shaft!

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