This will probably be useful (full copy provided to present CSCC C&A Officer):-
REPORT FOR COUNCIL OF SOUTHERN CAVING CLUBS CONSERVATION AND ACCESS OFFICER
Comprising:-
Executive summary
Recommendations
Brief
Findings
Fauna. Flora
Discussion
Hydrology
Appendix
EXECUTIVE SUMMARY
Whilst the deeper parts of the mine may appear to be in most need of work, the geology at shallower depths means that this is where work would be most beneficial in maintaining access to the mine as a whole.
The length of entrance passage up to and including the first junction is, of necessity, critical in maintaining access.
Those works might be broadly classified as P1 “do soon” and P2 “can be left to later”
In addition, some works to the trees above the entrance are recommended.
Some recommendations for the propping works are given in the Appendix.
RECOMMENDATIONS
For works at Compton Martin Ochre Mine
1 Entrance area: Seek the agreement of the land owner to remove the two trees above the entrance to reduce the risk of the rock, etc., covering the entrance. Priority 2.
2 Entrance passage: Props 2, 7, 8, 9, 14, 15 should be “paired”. Priority 1.
3 Entrance passage: Props 11, 14, 15 should be fitted with pairs of capping wedges, after pairing has taken place. Priority 1.
4 Props at Junction “A” should be paired. Priority 2.
5 At 12.2m in the entrance passage install pairs of new props either side of the area of roof which is delaminating. Priority 3.
6 Replace props 2, 7, 9 in the entrance passage due to condition. Priority 4.
N.B. The above recommendations are given following a visual survey carried out on Saturday 3rd February 2007, and are offered Pro-bono, and whilst care has been taken in the preparation, no responsibility can be taken for how they are implemented.
The objective of the recommendations given above is to allow access to the mine to be maintained for the foreseeable future. Further works will become necessary as the condition of props, or the geology dictates.
Due to the nature of the geology the possibility exists that a roof failure may occur at any time. Such a failure may be partial or total; however, a total roof failure may only lead to the creation of a natural arch.
Due to the layout of the mine any roof failure which is beyond junction “A” in the entrance passage, whilst a party is in the mine, could be avoided by the use of alternative passages.
Therefore the maintenance of the entrance passage including junction “A” is, by necessity Priority 1.
Brief
To report on the condition of passages in the mine, particularly in the entrance area, and to make recommendations as to what support works might be advisable.
Findings
NB all directions assume the person is facing into the mine. All lengths are stated from either the rear of the entrance tubes, or centre of the junction in the rear.
The entrance area:
The entrance is set in a man made hollow in the east side of the combe. The pre-cast concrete tube entrance is set below a steep slope, at the top of which is a rock face, surmounted by trees.
The two trees are native broad leaved species. The smaller is about 225mm diameter trunk, and the larger about 400mm diameter.
Adjacent to the area, and on the track below it, are 38 sections of telegraph pole, with a length of about 1.8 to 2.2 m.
The Entrance:
The entrance is formed from 4 pre-cast concrete tubes set horizontally. The entrance is secured by a grill formed from individual bars, one of which is retained in place by a padlock.
The joints of the entrance tubes are vertically miss-aligned, but this miss-alignment appears to be of long standing.
The entrance passage:
From the entrance to junction “B”. All distances originate from the rear face of the entrance tubes.
The first 20m of passage, up to junction “A” has a roof height varying from approximately 1.2m to 2.2m.
In the first 11m there are 14 roof props, which are hereafter numbered as encountered, first left then right, unless noted otherwise.
Prop Condition
1 Slight to medium softening of wood fibres, and loss of integrity.
2 Slight to medium softening of wood fibres, and loss of integrity. One deep area of rot observed. Fungal growth present.
3 Slight softening of wood fibres, and loss of integrity.
4 Slight to medium softening of wood fibres, and loss of integrity.
5 Appears sound.
6 Appears sound.
7 Deep softening, especially at the base of the prop. Slight softening on rear surfaces which could be examined.
8 Medium softening of wood fibres, especially at base of prop.
9 Slight to medium softening of wood fibres, and loss of integrity. One deep area of rot observed. Fungal growth present.
10 Medium softening, especially on rear face.
11 Sound, but capping folding wedges loose.
12 Appears sound, rear inaccessible.
13 On right. Appears sound, rear inaccessible, slight softening of wood fibres.
14 On right. Appears sound. No capping present.
15 On left. Footed in deads, so base cannot be examined. Slight to medium softening of wood fibres, and loss of integrity. No capping present.
At 12.2m the roof is loose, and the strata are starting to delaminate. There is a small roof fall, which does not appear to be recent.
At 14.5m there is a roof fall which does appear to be recent. The original props are crushed or buried. The roof strata are delaminating to form a natural arching action.
At 16 to 16.5m the original propping is grossly rotted. Prop 15 is on the left side. The roof stratum here appears competent.
Prop 16 is on the left side at 18.3m and is sound.
Prop 17 is on the right side at 18.8m and is sound.
Junction “A” is reached at 20m, where a passage goes off on the left side. At this point a fault in the original survey is noted. The recess on the right side of the passage is actually opposite the passage on the left side, not offset.
Continuing along the entrance passage from junction “A” a roof fall is situated 4m from it, where the roof strata have delaminated.
The left wall at 4 to 6m from junction “A” is supported (?) by a wall of deads with associated propping partially built into it, both of which are possibly of little value to the stability of the passage. The props all display medium to high softening of the wood fibres.
At 8m from junction “A” a second passage is found on the left side, and this point will be referred to as junction “B”.
The end working face is found at 13m from junction “B”.
The left side passage at junction “A”
This passage was not entered. What could be seen suggested a floor of backfilled deads, with a roof of varying competence.
The left side passage at junction “B”
This passage is mostly backfilled with deads, leaving only a crawling space about 800mm high. An old row of props on the left side of the passage is mostly buried in the deads, and rotten. The roof of this length of passage is jointed and blocky, but appears competent for the narrow span of the passage. This passage ends at a further junction, which will be referred to as junction “C”.
Junction “C”
At junction “C” there are two passages to the right, and one to the left.
The various roof props in this junction area are all rotted completely, and would afford no support to the roof. A small area of roof between the two passages on the right is delaminating, but should not cause a problem when it fails as the roof otherwise appears competent for the span, being massively jointed and blocky, with little sign of movement.
First passage to the right at junction “C”
This short passage, which was not entered, has a large amount of deads which have fallen across the entrance from either side. Those props which are visible are rotted, but the area of roof which could be seen appeared competent.
Second passage to the right at junction “C”
This passage curves to the right as it leaves junction “C”. The roof stratum which is visible is massively jointed and blocky, and appears competent for the span.
The existing props are rotted, and some are short of the roof, suggesting capping blocks or wedges have fallen out or been robbed by the miners in the past.
An in-filled connection is apparent in the right hand wall at 7m from Junction “C”.
At 9m from junction “C” the passage straightens, and at this point a flat bottomed rail of light section is visible in the floor.
At 12.5m from Junction “C” a left hand passage is reached, which will be referred to as junction “D”. In addition, if the left hand passage is entered for approximately one metre there is a drop in the left hand wall of approx 1.2m down into another passage.
Passage straight on from junction “D”
At 5m from junction “D” a passage loops off on the right hand side. At this point four flat bottomed rails can be seen, grouped roughly together, at floor level, trapped by deads laid over each end. The grouping of the rails suggests they are loose, therefore eliminating the possibility that DeCauville track was used in the mine.
From this point on there is extensive collapse of the walls of deads either side of the passage and a large roof fall exists at 11m, but otherwise the roof appears competent.
Walls of deads restart at 18m, and all associated props are rotted, but the roof continues to appear sound. A shallow recess in the left hand wall shows signs of past flooding.
The loop passage previously mentioned rejoins at 23m, and the end of this passage is reached at 32m from junction “D”.
Passage on left at junction “D”
This short passage ends at a roof fall, which was not examined, but appears to have been due to the existence of a deposit of softer rock existing above the roof strata. This would have held water, increasing pore pressure on the strata below, possibly precipitating this local collapse.
Passage down drop on left at junction “D”
Descending the easy step down, the passage is easily traversed, with the steepest floor angle observed so far in the mine. A junction with a side passage, at 6.5m on the right side, is passed while traversing the 13m to the next junction, which will be referred to as junction “E”. The roof props passed in this passage display moderate to severe rot, and many are leaning into the passage, not touching the roof.
Junction “E”
At junction “E”, which is a “T” junction, the passage goes to both left and right.
The right hand passage from junction “E”
This passage is entered by crawling over an infill of deads. The passage roof is nominally propped, but the props are of varying degrees of competence, and some do not even reach the roof, where the capping, or capping wedges, have been robbed by miners. However, the sloping roof strata appear competent.
The left hand passage from junction “E”
The passage was only entered for a short way, but the props which are visible are all extensively rotted. The floor is undulating, mostly likely due to an infill of deads from adjacent workings. The sloping roof strata appear competent for the span.
Fauna
A total of seventeen bats were seen. Most were grouped around junction areas, although roosting individually, not communally. A few were seen, mostly where the walls were recessed, along passage lengths.
Flora
Mycelium: associated with the position of fallen props.
Bracket fungi: on standing props, what are believed to be fruiting bodies were seen.
Discussion
The entrance area: It is considered that if the smaller of the two trees vertically above the entrance should be brought down by natural forces then two things might ensue:- the rock on which the smaller tree rests might be brought down, thus reducing support to the rock behind which supports the larger tree. If the larger tree should also fail, either after or with the smaller tree then the amount of large rock fragments, combined with the smaller pieces and associated soil may be sufficient to completely cover the entrance, thus cutting off air to the mine, and access.
From the entrance to junction “A” some props lack proper capping, thus reducing their ability to accept load without allowing roof movement to occur. In addition some props are showing signs of pockets of penetrating rot, as opposed to surface fibre softening, which will further reduce their safe working load.
From 12.2m to junction “A” whilst there are roof falls these appear to have exposed more competent strata, which is starting to form natural arches; the exception is the small area of roof at 12.2m where delamination may precipitate a roof fall on the entrance side, which may cause a blockage due to the poor wall geology.
From Junction “A” to the end of the entrance passage the quality of the wall and roof strata improves.
From junction “B” to junction “C” the short passage is assisted by the narrow width and the amount of deads placed in it, both of which help to ensure the roof in this passage is adequate.
At junction “C” a greater span of roof is encountered, and the improved geology is more evident, although it is never of first quality. The walls placement and spacing appear adequate, although the isolated wall between two passages shows some distress.
Beyond junction “C” all passages, to varying degrees, show an improved geology, with apparently adequate strata for the roof spans.
The roof fall at the end of the short dead end beyond junction “D” is a reminder that the geology can never be fully relied on, as concealed intrusions or inclusions can weaken the roof in a way which cannot be seen.
Hydrology:
Water was evident on many surfaces throughout the mine.
Some drips were observed coming from, or close to roof faults.
A few depressions in the floor show signs of having held water.
No flows of water were observed.
APPENDIX
Suggestions for increasing the effectiveness of propping works.
Each prop should be fitted at the time of installation with a pair of capping wedges. These should be formed from the most durable wood available as they will be in constant contact with the rock face. The wedges should be formed from a piece of wood the same width, or slightly greater, as the top diameter of the prop. The length of the piece of wood should be slightly greater than the diameter. The depth of the piece of wood should be approx 20mm thicker than the gap between the top of the prop and the rock. Alternatively the length of the prop can be cut to leave a gap to the rock surface about 20mm thinner than the thickness of wood available to be used as capping wedges.
The piece of wood should be placed on its narrow side and cut through, preferably by band saw or small toothed hand saw from corner to diagonal corner.
(It is recommended that cut surfaces of wood treated with preservatives should be given a flood coat of preservative prior to fixing, to increase the in-service life.)
Thus when the two wedges formed are placed with their sloping faces together they will have the upper and lower surfaces parallel. Driving the two wedges together in this position will create a considerable force on the upper and lower surfaces, which will ensure the wedges give the best possible transfer of possible roof forces into the prop.
It is recommended that capping wedges are driven from both sides at the same time. This should ensure that the wedges are equally engaged with each other over the top of the prop, instead of one fully engaged and one only just partly over the prop.
The minimum size of hammer used in propping works for driving wedges, etc, should be a 7lb sledge hammer. The exception to this is for entering wedges, and nailing.
When changing capping wedges on existing props the pairing prop either side should already be in place. The new capping wedges should be cut and ready to hand.
Where the roof shape at an existing prop will not allow a single full width wedge to be used, and two pairs of narrower wedges would allow greater engagement with the roof area, then the opportunity should be taken to install this arrangement.
Where holes exist in wood to be used as props then these should be plugged with similar wood, to close off a possible way for rot to get easily into the centre of the prop.
New props should be founded on a bed preferably of level small stone (say 10mm to 20mm single sized) to allow the foot of the prop to drain. Where the intended prop position may hold water it would be preferable to infill with small stone. All stone beds should be tamped down hard using a 7lb sledge hammer.
Where a prop length is needed which cannot be passed around the bend at the entrance then the judicious use of foot blocks and capping blocks may make up the desired length, coupled with double pairs of capping wedges if absolutely necessary.
Many thanks to Fred Tye for the Report
Departed CSCC C&A Officer
I'll be there- my oversuit almost looked normal again, can't be having that 
