Tubbing

Technical | Shafts | Details > Tubbing

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During the sinking, heavy feeders of water of up to 1000 gall/min were encountered in the Magnesian Limestone and the upper sections of the coal measure strata. In order to overcome these feeders the shafts were lined with cast iron tubbing. This was was of the “English” type with 10 segments per ring, secured by means of wooden wedges inserted between the tubbing and the shaft wall and with thin wood sheeting between the vertical and horizontal joints. In the North shaft there were integral brackets and boxes cast-in to hold the timbers supporting the shaft guides.




		Typical cast iron English tubbing. (JST)

In 1891 the manager, J.C.B. Hendy, wrote:

‘The thickness of the tubbing is ¾in, 1½in and 1¾in. The top segments being 2ft 6in by 4ft 6in and the lower 2ft by 4ft 6in’.

The thicker sections would be used to cope with the increased water pressure as the depth increased. Whether they were arranged in this way between each wedging curb (a support ring acting as a water barrier) or over the full depth of the tubbing is unclear.

The tubbing is documented as starting at a depth of 18yd, but at the fan-drift entrance said to be at 30yd the South shaft appears to have been lined with brickwork and there is no sign of tubbing. There is some question as to whether the depth of 30yd is correct since there are a couple of other measurement errors given in the source of the information. It may be, however, that this was just a short isolated section of brickwork between two sections of tubing. The fan-drift itself appears to have been fairly dry, so either the strata was dry at this level or the fan-drift brickwork also had some form of waterproofing.

During sinking, 350 galls/min of water were encountered at a depth of about 40 yds.




		Lip of South pit fan drift entrance. (FoPP/JST)


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11 Nov, 2011


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