928 THE COLLIERY GUARDIAN. November 5, 1915. Collapse and Recovery of Central Incline Shaft, Bantjes Consolidated Mines Limited.* By PERCY CAZALET This shaft is a five-compartment one, with four skip- ways and a ladder way, the outside dimensions being 33 ft. by 7 ft. 6 in., and the grade 34|degs. -The shaft pillar is nowhere less than 330 ft. wide, the reefs not being stoped within 150 ft. of the side of the incline, or within 200 ft. from the cave. Figs. 1 to 3 give details of the shaft and equipment, and also shows the steel setts with w’hich the excava- tion of the shaft was framed. The method by which the tracks are laid on continuous concrete stringers, instead of on timber sills, is also shown; the work of recovery was made much easier on account of having these con- crete stringers to work from. The track and stringers were found intact under the fall, although the steel uprights, which were embedded in the concrete to a depth of 14in., were bent in places at right angles flat on to the stringers. Figs. 4 to 6 show two cross sections through the shaft, and convey a good idea of the geological features. The subsidence • was due to the decomposed dyke becoming saturated with water from the heavy rains, and W. W. LAWRIE. all ore and material. It wras therefore decided first to recover and timber the two eastern compartments, and to equip the winze which had been sunk to the first level as a ladder way,-leaving the recovery of the remaining three compartments until the ground had settled and drained, possibly towards the end of the present dry season. In re-opening caved areas of any description, the removal of the broken rock is the principal factor in the speed of advance. In the initial stages of our work we were much delayed by this difficulty, which was over- come by opening up a rise in the channel between the concrete stringers in the east compartment (the steel girders and lagging of the setts, which were resting on the rails, forming a natural cover), and small curved plates were laid down on the bottom of this rise to form a chute. This work was difficult, but when completed made all the difference in the speed of advance. In order to control the size and amount of rock passed down this chute, and thus prevent it from becoming choked, an 8in. pipe, 9 ft. in length, was laid in the Five complete setts of timber were used, consisting of 10 in. square caps, 14 ft. long, made in two halves for convenience in handling, with a scarf joint in the centre. The legs or dividers were of 10 in. by 8 in. timbers, 3 ft. 6 in. long. The setts were tied together with studdies and chains, with short hook bolts, instead of the usual hanging bolts. The chains and hook bolts allowed of a great variation of centres, and enabled the setts to be easily taken adrift. The height of the travelling setts depends on the height of the permanent work to be put in. They should be of such a height that the permanent caps do not interfere with the free use of the hammer when driving the rails, while at the same time giving the maximum height possible for conveni- ence in working. Steel plates, Gin. by Jin. (to reduce friction) were bolted on the caps, and to ensure that the rails travel parallel to the shaft, the caps should be pegged, the distance between the rails being Gin. If this is not done, it is found that the rails tend to collect towards one end of the cap. To prevent the setts from travelling downhill as the fallen ground was drawn off in advance, every second sett was anchored back by two long l|in. steel hoisting ropes, provided with large turn buckles at their upper ends for making them taut. The driving of the rails presented no difficulties, travelling right through the full 95 ft. of fall with very few renewals, and with but little exertion on the part of the native strikers. B --- VIEW DOWN SHAFT ---- 60A rail HOLDING-DOWN BOLTS SECTION on AB Figs. 1 to 3.—Central Incline Equipment. Figs. 4 to 6.—Sections through Central Incline. TRANSVERSE SECTION LONGITUDINAL — SECTION -- — ON AB — 1^+ + ■r.j-cz~iL~-iiz I JI I IN+ UnafoAr&f 11 Quafyxite |_| + + and being converted into a plastic mud, with little or no “internal friction.’’ The whole weight of this saturated mass was thus applied to the capping of sand- stone, which forms the immediate roof of the shaft, which latter fractured under the stress, throwing the weight on to the steel shaft framing, which collapsed with practically no warning. The sides of the shaft remained intact and solid, and showed no signs of pressure. The steel setts totally collapsed for a distance of 95 ft. (from 125 ft. to 220ft. from the collar of the shaft), while a further 35 ft. partially collapsed. The vertical distance from the surface was 65 ft. at the top end, and 115 ft. at the bottom, or, say, 90 ft. at .the centre of the fall. The first object being to save the mine from being flooded, and especially the main pumping station on the 10th level, and at the same time to get more information as to the nature of the fall, an attempt was first made to recover the west or ladder compartment. In three days we had advanced 20 ft., when the difficulties met with were so great that we realised we could not hope to get through in time to save the pumps. A winze 85 ft. in depth wTas therefore started from the west side of the shaft, above the fall, to the first level, and a second winze of about 20 ft. from the first level into the incline below the fall. The capacity of this shaft is such that only two com- partments are at present necessary for the handling of *From the Journal of the South African Institution of Engineers. chute at the face of the fall, and moved forward as the face advanced, the broken rock being hand-fed through this pipe into the chute, and carried down with a stream of water. For dealing with material and concrete, as well as for hoisting broken rock, a temporary 3 ft. track w’as laid between the rails of the main track, on which ran an ordinary drill trolley, 7 ft. G in. in length, and 12 in. in depth, and 2 ft. 9 in. wide. For cutting through the bent and twisted steel setts, the oxygen-acetylene flame was used. From the experience gained in the preliminary work, it was evident that we had to deal with running ground, consisting of badly crushed, rotten sandstone, with water-logged, decomposed dyke above, and it was recog- nised that “ spiling ” in some form or other was neces- sary in advancing through the fall. After much thought and discussion it was decided to depart from the methods which have usually been employed in work of this kind on these fields, and to adopt the method we had developed while working in the ladder way. This method is really a modification of that employed in tunnelling through loose ground by means of advanced casing pushed forward by hydraulic plant, followed by per- manent brick or other casing built up in sections as the work advances. In this example the advanced casing was represented by four to five travelling sqtts of timber supporting 15 ft. lengths of 45 lb. rails. These rails were driven forward with 141b. hammers. As they advanced the broken ground was cleared from under them at the face, and a sett of timber erected, the rear sett being taken down. The permanent caps were of 10 in. by 10 in. pitch pine, fitted on the top with boxing (see figs. 7 to 13), which makes it possible to place short lagging on the caps and to renew this lagging easily. The caps were put in at 20 in. centres, and were hung from one another by lin. bolts and links. The safe distance which the travelling setts could be advanced ahead of the perma- nent work was not more than 22 in., and that distance was only obtained by putting the short lagging into the boxes on top of the last permanent cap, and keeping them in place by spikes through temporary blocks nailed at the side of each box. The permanent caps, after being placed in position under, and as close as possible to, the lagging, and after the links and bolts had been fastened up, were jacked into position by two 50-ton hydraulic jacks. Attempts were first made to support the caps on 10 in. by 10 in. dividers, resting on 6 in. soft wood footboards, with a 5 in. hard wood corbie against the caps. These dividers stood the pressure all right, but it was found impossible to prevent the caps from being forced down the shaft, and thus taking the dividers out of the square, even when these were set as much as their own width out of the normal. It was, of course, impossible to put in bearers, on account of the running nature of the ground, and the only other alternative was to anchor the setts with wire ropes. These ropes (l|in. steel hoisting ropes) were anchored to the concrete stringers higher up in the shaft, and fastened to the caps by means of l|in. eyebolts. They were from 60 to 100 ft. long, and were made taut by large turnbuckles. The creep of the caps continu-