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The western tunnel is Charlton Lane Tunnel 154 yards.
The eastern tunnel is Mount Street Tunnel 121 yards.
It is not known which tunnel the cave is located in.
At the very least Network Rail must impose an immediate and strict speed limit through the tunnels of 5mph until thorough investigations can be carried out. "Thorough" means taking up all tracks through both tunnels and carrying out a tight 1m borehole grid until the cave is located. It must then be surveyed and made completely safe to modern civil engineering standards.
The article describing the cave appeared in the Kentish Mercury on Saturday March 24 1849. It provides unequivocal and undeniable evidence that the cave is located directly underneath the tracks currently in daily use. Not only is the condition of the 150-year-old shoring unknown, but also the condition of the chalk passageway (part of an unknown denehole or chalk mine) may well have deteriorated - galleries of this type have a hard enough time remaining in good condition without weight or vibration.
In the absence of knowledge about the current condition of the cave, this tunnel is a tragedy waiting to happen. Network Rail must act immediately.
↑ Click for a larger version (641k 825 x 1000)
↑ The railway tunnels in about 1880 - click for a larger version (1.1Mb 1200 x 805)
Here is an exact transcript:
DISCOVERY OF A CAVE IN HANGING WOOD. -During the operations of the workmen on the North Kent line of the South Eastern railway, when tunnelling under the hanging woods, at Charlton, near Woolwich, they came upon a cave, of considerable dimensions, cut in the chalk and flint rocks. A great quantity of sand has fallen at one end, blocking up the side from which it has apparently been entered, and the workmen are now busily employed in shoring up a part of the roof of one of the chambers, the railway passing over its entire breath. Four chambers have been discovered, forming alternate recesses, from the main cave leading in a westerly direction. The roof of the cave is on a level with the line of railway, and the base 12 to 14 feet lower. The atmosphere in it is remarkably dry and pure, and presents a great contrast with the damp and close atmosphere experienced in passing along the tunnel to the extremity where the cave has been discovered. The men state they found a knife and a spoon on exploring it, and they turned their discovery to good account on Sunday, having lighted the whole of the tunnel with candles, and conducted visitors over the cave at the extremity, charging them 3d. for admission.
Is the cave a denehole or a chalk mine?
Deneholes are known to have existed at Hanging Wood. F.C.J. Spurrell notes the presence of deneholes at Charlton in the Archaeological Journal XXXVIII (1881):
In the direction of Charlton are some. The late Sir T. M[aryon] Wilson told me of several, and that one which fell in at the east end of his avenue was examined by him. He mentioned several which once existed at Hanging-wood
However, the description above of four chambers forming alternate recesses in a "main cave" steers my opinion slightly more towards this being an orphaned section of passageway from a chalk mine of unknown extent. This is a very important issue, because if this is a chalk mine, there may be further mine galleries under the railway that were not discovered while driving the tunnels in 1849. This aspect underlines the importance of using a tight borehole grid throughout both tunnels and the open section of track between them to locate any voids.
How old is the mine gallery?
The gallery was part of a disused mine working; it's impossible to say how many years before its rediscovery it was abandoned - maybe only 10-20 years, maybe 100+ years. If it is a denehole, then it may be up to 800 years old. The age of a chalk working doesn't necessarily predict its strength and stability - some of the Victorian workings under Alliance Road in Plumstead were highly dangerous, with numerous roof collapses occurring, wheras we have been in 700-year-old deneholes which are still in excellent condition. Whatever the age of the chalk working under the railway, it must be found and inspected.
After finding the mine working, then what happens?
The first question that must be asked is whether it's a denehole or part of a chalk mine. If it's a normal denehole, then it will be a self-contained working of a small size. If it's part of a pillar-and-stall mine working (similar to Chislehurst Caves), then the sand fill described as blocking one end of the gallery must be safely dug through, supporting the roof to protect the workers, to investigate if the gallery continues. The attitude must be to suspect that there are further unknown mine galleries under the railway line, and to search exhaustively to remove all doubt. It should be added that deneholes tend to occur in clusters, so there would still be a risk of other unknown deneholes nearby whose chambers might also undermine the railway.
What if boreholes in/between the tunnels find previously unknown galleries?
All new passageway must be entered and surveyed, and a complete plan drawn up of the mine working. If the working is very extensive, the most cost-effective solution is localised filling/strengthening near the railway, with permanent access points created which allow regular inspections of the rest of the mine to check for deterioration.
In the direction of Charlton are some. The late Sir T. M[aryon] Wilson told me of several, and that one which fell in at the east end of his avenue was examined by him. He mentioned several which once existed at Hanging-wood
However, the description above of four chambers forming alternate recesses in a "main cave" steers my opinion slightly more towards this being an orphaned section of passageway from a chalk mine of unknown extent. This is a very important issue, because if this is a chalk mine, there may be further mine galleries under the railway that were not discovered while driving the tunnels in 1849. This aspect underlines the importance of using a tight borehole grid throughout both tunnels and the open section of track between them to locate any voids.
How old is the mine gallery?
The gallery was part of a disused mine working; it's impossible to say how many years before its rediscovery it was abandoned - maybe only 10-20 years, maybe 100+ years. If it is a denehole, then it may be up to 800 years old. The age of a chalk working doesn't necessarily predict its strength and stability - some of the Victorian workings under Alliance Road in Plumstead were highly dangerous, with numerous roof collapses occurring, wheras we have been in 700-year-old deneholes which are still in excellent condition. Whatever the age of the chalk working under the railway, it must be found and inspected.
After finding the mine working, then what happens?
The first question that must be asked is whether it's a denehole or part of a chalk mine. If it's a normal denehole, then it will be a self-contained working of a small size. If it's part of a pillar-and-stall mine working (similar to Chislehurst Caves), then the sand fill described as blocking one end of the gallery must be safely dug through, supporting the roof to protect the workers, to investigate if the gallery continues. The attitude must be to suspect that there are further unknown mine galleries under the railway line, and to search exhaustively to remove all doubt. It should be added that deneholes tend to occur in clusters, so there would still be a risk of other unknown deneholes nearby whose chambers might also undermine the railway.
What if boreholes in/between the tunnels find previously unknown galleries?
All new passageway must be entered and surveyed, and a complete plan drawn up of the mine working. If the working is very extensive, the most cost-effective solution is localised filling/strengthening near the railway, with permanent access points created which allow regular inspections of the rest of the mine to check for deterioration.
↑ Charlton Lane tunnel - click for a larger version (957k 1000 x 978)
↑ Mount Street tunnel - click for a larger version (900k 1000 x 990)
How much did railway locomotives weigh in the late 1840s?
The Jenny Lind, a highly successful and much-copied design of the late 1840s weighed only 24 tons.
Today the typical maximum single axle load on the North Kent lines is about 20 tons - not far off the entire weight of Jenny Lind, whose modest weight the 1849 shoring underneath the tunnel would have been designed to support. The individual bogies of new generation locomotives used on this line each weigh about 60 tonnes.
To expect the shoring under the tunnel to withstand present-day axle loads and bogie weights is insanely optimistic.
