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June, 1958

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The first part of this article described the preparatory work, the freezing of the shaft and the first stages of the sinking in which a cast-iron tubbing was used. In all, 24 rings were required for this part of the lining.

Segments were left out in rings 7 and 8 to allow for the entry of the 24-in, diameter ventilation range which passes underneath the foreshaft. When the pipe range was in position, the remaining gap was filled with brickwork and concrete.

This part of the shaft was kept vertical by the use of four side lines suspended from ring No. 1 and the contractors state that in no place in the cast-iron section of the shaft was it more than 1/8 in. out of plumb.

A concrete wedge was constructed below the last ring (No. 24) to form a support for the lining above and a key for the next length of walling. Before this excavation was attempted, it was necessary to underpin the cast-iron lining and this was done using 15 vertical R.S.J.s, 6 ft. in length (Fig. 2). These girders, with steel plates top and bottom, were placed around the shaft; timber packing was placed between the top plates and the base of the lining which were bolted together. Bed boards were wedged below the bottom plates to make the whole structure rigid. The wedge was then formed and concreted, with a water garland built in at the top of the concrete.

This part of the sinking took 21 working days.

Permission had been granted by H.M. Inspectorate of Mines to use a crane at this stage of the sinking. The crane, manufactured by Rushworth Brothers Limited, Lancashire, was a 5-ton electric derrick crane of the two-motor type, fitted with a 65 ft. jib and arranged for two-speed operation. It is now used for loading materials to the batching plant and is working with a 27/22 cu. ft. single-chain "Priestman" type grab having a loaded capacity of 50 cwt. This load is hoisted in the fast gear at approximately 100 ft. per min., but the crane can be used as a standard hoisting machine and can lift loads up to 5 tons in the double gear at approximately 40 ft. per min.

The hoisting and derricking motions are driven by a 25 h.p. totally-enclosed, slip-ring motor and the slewing motion is controlled by two upright drum-pattern crane controllers. The crane, suitably anchored to concrete bases, is shown in Fig. 13.

While awaiting delivery of some headgear components, a further 30 ft. was sunk using the crane. This section was lined with a 3 ft. concrete wall and a supporting wedge was cut at the 60 ft. level.

It should be remembered that until the frozen ground is passed through, the circulation of brine in the freezing tubes is continuous. By the use of modern instruments, a constant watch is kept on the brine flow to detect any leakage, and any hitch in the smooth-running of the plant is quickly detected.

Winding equipment

On October 15, 1956, sinking was re-commenced using the proper sinking and winding equipment which had been erected during the interval of freezing.

Double-hoppit winding is employed which necessitates the use of a double-drum sinking winder. The winder, manufactured by Metropolitan-Vickers Electrical Co. Ltd., has a maximum speed of 20 ft. per sec. with a maximum load of 3 tons of dirt. One drum is fixed and the other is clutched to allow for the constant change in hoppit landing levels.

The two guide ropes for each hoppit are provided by the four-drum capstan winch, which raises and lowers the double-deck scaffold.

Manufactured by John Wood and Sons Limited, Wigan, the winch is one of several supplied to the N.C.B. for new sinkings, and after service at Wearmouth, it will be transferred elsewhere to a new site.

The general duty of the winch is as follows —

Maximum depth of sinking	5,600 ft.
Maximum load to be lifted per drum	20 tons
Maximum load to be lifted by the winch	40 tons
Maximum holding duty per drum	25 tons
Maximum holding duty by the winch	50 tons
Rope speeds — maximum	12 ft. per min.
Rope speeds — minimum	10 ft. per min.
Rope	3 7/8 in. circ. (l.c.)

Each winch is arranged for driving from a compressed-air or steam reciprocating engine or alternatively by an electric motor. At Wearmouth, the winch is steam driven thus giving a second method of withdrawing the men in case of a failure in the power supply to the electric winder.

The drums of the winch are each driven by an individual worm drive and mitre wheels from the main countershaft. They are 5 ft. in diameter and 4 ft. wide, with flanges 9¾ in. deep.

Each of the four clutches are of the positive-jaw type and they are so arranged that the clutch cannot be withdrawn before the brake is applied or the brake released before the clutch is engaged.

A view of the winding house showing the winding engine and scaffold winch is given in Fig. 19.

Blasting

Another of the advantages of using the freezing method is that conditions in the shaft bottom are conducive to good workmanship and also mechanical mucking is simplified due to the absence of a sinking pump and sump.

From the beginning it was intended to use mechanical mucking, and the two methods which were considered were a grab slung from the walling scaffold and an Eimco shovel mounted on crawler tracks.

With this in mind, blasting trials were carried out in the shaft bottom using Cordtex fuse and the contractors suggest that it has the following advantages over the more conventional method of blasting.

(1) It is safer when used in conjunction with mechanical mucking, as only about 16 detonators are used against 100 or more which would normally be required.

(2) Cordtex enables the charge to be spaced or decked in the shot hole, instead of it all being placed at the bottom, thus the charge can be adjusted to suit the varying degrees of hardness which are met with in a round.

(3) More uniform fragmentation can thus be achieved.

(4) A shorter time is required to charge up a round of shots.

Apart from the trials outlined above, blasting is carried out using Polar Ammon gelignite and short delay detonators. The lead wires are waterproofed using plastic sheaths and the shotholes stemmed with brine. All shots are fired from the surface.

The holes are drilled by Ingersoll-Rand pneumatic drills using Sandvik Coromant drill steels and normal cross-bits.

At the time of writing, the best rate of advance so far obtained had been 48 ft. per week.

Drawings and Photographs accompanying the article