Wellington A Purdon recounts the construction of... Woodhead's first tunnel

Wellington A Purdon recounts the construction of… Woodhead’s first tunnel

Situation and character of the work/geology of the ridge/general design and structure/plan of construction/preliminary operations

The range and levels

Ventilation of works/drainage

Sinking of the shafts

Driving the headings/excavation & lining

About the author

Sinking of the shafts

The process of shaft sinking and drawing out the water and material is familiar enough in the colliery districts and the practice observed at this tunnel did not differ materially from that in general use so that it does not require to be minutely detailed. Shafts of three times the depth and difficulty of those in question have been successfully accomplished; but it may not be out of place to give a short general description of the sinking etc to perfect the object of this paper.

The centre point being fixed and the size of the shaft determined, it was described on the ground with a radius 12 inches greater than the nett dimensions, to admit of the sides being lined with masonry for some short distance down. The first material generally met with was a thin bed of peat, resting on gravel and loose rack, which merged into a bed of shale or sandstone, into which the sinking penetrated a few yards before the foundation course of the walling was laid. This was set upon a timber curb and carried up in a regular manner. The depth to the foundation of the walling might be perhaps 10 yards.

The sinking then proceeded for 20 or 30 yards without any particular occurrence; but little water was encountered and the only means used for winding out the material was at first a windlass and then a horse gin. After this depth, however, a quantity of water was generally met with, proceeding from a bed of open sandstone, which overpowered the lifting capacity of the two 100-gallon water barrels. This, of course, stopped the sinking until the engine was got ready. In the meantime, the delivery driftways before mentioned were driven and the requisite cross beams for supporting the pumps were inserted as far down as the surface of the water in the shaft. As soon as the engine was erected and the winding and pumping gear got into action, the water was lifted out of the shaft and the sinking resumed. The various strata were then passed through and, when a certain depth was reached, it was found expedient to break the lift of pumps as before described and the lodges were formed in the manner stated. When possible, the lodges were driven in a bed of shale that required no puddling except behind the dam. When in open rock, all round the sides and at the bottom required to be puddled.

When the level of the next lodge was reached, the second lift was broken and the sinking proceeded with to a depth of 3 yards below the bottom of the tunnel, where a chamber was excavated nearly similar to the lodges and capable of holding 10,000 gallons of water. In the event of any derangement of the pumping gear, this served to keep the workings dry for a few hours by collecting the water till the necessary repairs were made.

The material being entirely beds of sandstone and shale, sufficiently solid to stand without lining, no further walling than that described was requisite, except at the lodges where a casing of masonry, summered to the centre of the shaft, was introduced for a vertical space of 5 feet to resist the pressure against the puddle dam in front of the water lodge.

Though walling was not required to retain the strata, it was however found necessary to sheet the sides of the shaft with inch boards in order to conduct the water issuing from the strata at different elevations, down the sides of the shaft at back of the boards, so as not to shower on the workmen and occasion interruptions by extinguishing the lights etc.

The manner of fixing this sheeting was to fit a ring of elm, 5 inches square, round the shaft, a space being first cut out of the rock in which it was inserted and wedged in a truly central position. This was repeated at every 12 feet of the vertical range, with occasionally an intermediate one when the rock was friable. Inch boards were then nailed to the wooden rings, having their side joints vertical and closely fitted, and of lengths so adjusted that their ends met against each other in a butt joint upon the sheeting rings. The shaft was thus kept dry and shapely, and the small loose particles of strata were prevented from dropping from the sides, down upon the workmen.

A vertical section of a shaft showing a garland ring.

It was also found expedient to insert, at intervals, what is termed a garland or gathering ring (see above). This was somewhat similar to that described for the sheeting, being likewise 9 inches thick, but it was 5 inches wide with a semi-circular channel in the upper side, 3 inches deep. This collected the water which flowed adhesively down the sheeting boards and the side of the shaft, and being a little inclined to the horizon, it discharged the water at the lowest point by a pipe into the next adjacent lodge whence it was raised, without descending to the bottom of the shaft, from which it should be lifted at a loss of power.

It may be mentioned that the sheeting could not be carried down close upon the sinking as it would have been destroyed by the blasting. It was sufficiently safe, however, when a space of 10 or 15 yards was left between, until the bottom was reached, when it could be carried down entirely.

The winding gear and pumping apparatus will be best understood by a reference to diagram below.

Section showing the head stocks, winding and pump gear at right angles to the line of the railway.

Upon the extremity of the fly-wheel shaft of the engine was fixed a spur-wheel that drove two pitched wheels, one attached to the winding shaft and the other on the cranked shaft that gave motion to the L legs at the top of the pit, from which the pump rods were worked. There were two verticals stacked upon the winding shaft to guide the coils of ropes that passed from thence over a wheel on top of the head gearing of the pit so as to hang into the shaft in the required position and suspend the skips in which the material was hoisted, about two tonnes at a time. There was also a round rope, 3 inches diameter, used for raising or lowering the heavy lifts of pump-trees and worked by a powerful capstan, acting at right angles to the winding ropes.

Plan of trap doors and balance weights.

Trap doors were contrived over the mouth of each pit after they were sunk to the bottom which being hinged in halves and balance-weighted, the residuary weight was lifted by a hand-gearing when a skip passed up or down and the doors flew open to admit it (see diagrams above and below). There were rails laid on the upper surface of the doors and, when laid down, a lurrie frame was wheeled on to them and under the skip, to carry it away to the spoil bank.

Diagram showing the action of the balance weights.

There were two sets of guide rods, of 1¼ inch round iron, stretched vertically down the shaft from the top of the head gearing and keyed under a beam at the bottom of the shaft, which prevented the skips from swinging about or coming in contact with each other or with any of the shaft timbers etc. One skip was always up when the other was down. This was arranged by coiling the ropes in opposite directions upon the verticals. The guide rods were put together in lengths of 30 feet and jointed like the old fashioned legs of a surveying instrument. They were so strained that when struck by a bar at bottom they sounded like a harp string and certain understood taps served as signal to the engine man to lower or raise as required.

The time occupied in sinking the different shafts, differed considerably. They were all commenced in the autumn of 1839, and were sunk about 30 yards deep at the end of the year. The sinking lingered at this stage for about six months, during which time the engines and pumping apparatus were got ready, and about July 1840, the sinking was resumed and continued in the different shafts with various success.

ShaftDepthTime to sinkBottomed
No. 1186 yards3 years 1 month29th Oct 1843
No. 2192 yards4 years 5 months31st March 1844
No. 3165 yards2 years 7 months30th April 1842
No. 4196 yards2 years 3 months31st Dec 1841
No. 5138 yards2 years 1 month30th Oct 1841

The depths here expressed are taken from the bottom of the sump, below the level of the tunnel to the surface, which was in some cases artificially raised to admit a tip for the spoil when the ground was flat.

Looking at the periods and spaces of time herein set forth, it will be seen that shafts Nos.1 and 2 took a much longer time to sink than the others. The cause of this was no doubt owing to the great quantity of water; but it is not to be supposed that the difference of time was continuously occupied in sinking. It arose from other difficulties. The work was frequently interrupted by the breaking down of the pumping machinery and consequent delays in removing the accumulated water. It was sometimes found that the sinking tapped quantities of water that were backed among the strata which at first overpowered the engine but were overcome after a few weeks by the continued action of the pumps. The supply then became constant and limited. No.2 shaft received a clear check of 12 months in addition to the six months that, in common with all the shafts, were lost at the first getting to work of the engines and pumps. The water was so excessive that a second engine and additional set of pumps had to be prepared and applied, and even this did not prevent the necessity and of course delay of coffering the shaft through some heavily watered beds of rock with layers of impervious strata at top and bottom by which means the draw from the shaft was relieved.

At No.1 shaft, a boiler burst on one occasion and blew the engine and bed to pieces. It took several weeks to repair and get the water out again.

In stating the rate of sinking, such long intervals of delay as I have mentioned, may be taken as exceptional. There were, besides, countless delays arising from ordinary casualties which may more rationally be said to belong to the process of sinking and viewed in this light. I am of opinion that about 2 yards a week would best express the general rate of progress.

The quantity of water drawn out of the shafts while in progress of sinking has been approximately estimated, the pumps being supposed to average 14 strokes per minute.

No. 1582,568 tonnesNo. 4306,131 tonnes
No. 2699,223 tonnesNo. 5400,869 tonnes
No. 3399,455 tonnesTotal2,388,246 tonnes

Quantity of water drawn out of the shafts after they were sunk –

No. 1123,725 tonnesNo. 41,027,271 tonnes
No. 2210,686 tonnesNo. 51,070,398 tonnes
No. 3942,431 tonnesTotal3,374,511 tonnes

The total quantity of water lifted by the pumps during the construction of the tunnel amounted to 5,762,757 tonnes which would fill a cubical cistern of 197 yards square.

The average depth of all the shafts was 515 feet, but the height to which this quantity of water was raised of course depends upon the level in the vertical range of the shafts, from which certain portions of the water were lifted, not only during the progress of sinking but afterwards; and from the best data that exists for forming a judgement, it must be about 350 feet, which gives us an idea of the work performed, viz – 5,762,757 tonnes lifted 350 feet high in 4½ years. This is equivalent to 58.33 horses, working for the same period.

To conclude this part of the subject, when the tunnel was finished, the quantity of water that was continually passing away by the two side drains at the western face indicated a discharge of 1,064 gallons per minute; the velocity being about 3.4 feet per second and the sectional area 120 inches; that is, two side drains each 12 inches wide and 5 deep. The discharge of the pumps from the five shafts may be taken at 660 per minute (six pumps, working 14 strokes per minute).

The difference may be supposed as the discharge belonging to the western face stretch which was never lifted, viz – 404 gallons per minute.

Situation and character of the work/geology of the ridge/general design and structure/plan of construction/preliminary operations

The range and levels

Ventilation of works/drainage

Sinking of the shafts

Driving the headings/excavation & lining

About the author