SHAFT SINKING ON THE PROPERTY OF BUFFELSFONTEIN GOLD MINING COMPANY LIMITED

By J. CASEY (Associate Member) – The Certificated Engineer Jan 1965

 ABSTRACT

Details of the layout of the main shaft and a ventilation shaft at Buffelsfontein mine and the equipment used to sink, line and equip the shafts, including the winding plants, the multi-deck stages, the lashing equipment, and the concrete mixing plant. Tables give personnel required, the progress of sinking and cost of sinking Arrangement of permanent skip loading apparatus and automatic control.

CONTENTS                                                    

1.      Introduction

2.      Shaft layout and headframes

3.      Winding equipment

4.      Multiple deck sages

5.      Lashing equipment                                     

6.      Shaft lining

7.      Concrete mixing plant

8.      Stripping and equipping the shafts

9.      Ventilation during sinking

10.  Sinking statistics

11.  Permanent loading arrangements

12.  Conclusion

13.  Discussion

14.  Author’s reply to discussion

 1.      INTRODUCTION

To exploit the eastern zone of the mine property and to assist in increasing production it was decided to sink a further two shafts, 200 feet apart, one being ca foot diameter main downcast and the other a 22 feet diameter upcast ventilation. Both shafts were to be lined with monolithic concrete and were to be 5 300 feet deep. The 22 feet diameter ventilation shaft is designed to upcast 1 400 000 C.F.M. of air against a resistance of 22 inches water gauge.

The Main shaft is designed to hoist a minimum of 160 000 tons of rock per month, to transport persons and material and to allow air for ventilation to flow down it. The shaft is divided into six winding compartments and has two recesses to accommodate the power cables. Extensive use of scale models during the preliminary planning stages proved useful in deciding on the design and layout of stages, shaft buntons, bunton pockets, guide cleats, station shuttering and the arrangements for handling rock, spillage, and water these models also proved invaluable in determining the walling routine. Normal working conditions could be simulated and preliminary training of crews was made possible.

Although no claims are made to any innovations in the shaft sinking technique, the benefit was gained by selecting the most suitable practices and ideas used at other mines. The time and money spent on detailed planning of shaft layout, design and equipment and the extensive use of jigs and the scale models, was not wasted and contributed to the success of the final result.

2.      SHAFT LAYOUTS AND HEADFRAMES

On the surface, the shafts were laid out as in Fig. 1. The Ventilation shaft is 200 feet north of the Main shaft. Both shaft collars were sunk and lined with concrete to a depth of approximately 200 feet after consolidation and cementation of the surrounding area. The surface and sub-bank layouts were completed before sinking operations were commenced. The layout is such that all persons enter or leave the conveyance at the sub-banks. Europeans pass along a tunnel between the change house and the shaft while the Bantu pass along a tunnel connecting the shaft to the crushed building in the compound enclosure. A steel A-frame headgear was erected over the Ventilation shaft and a concrete square shell-type headgear was provided for the Main shaft. It was decided to sink, line and strip the Ventilation shaft before commencing to sink the Main shaft. To achieve this the north permanent winder for the Main shaft was erected and the ropes were deflected by sheaves on the ground so as to pass over the sheave wheels on the headgear of the Ventilation shaft. (See Fig. 2.)

3.      WINDING EQUIPMENT

For the sinking of the Ventilation shaft, the kibbles were operated by the north winder for the Main shaft. This has a double drum, 16 foot in diameter, and is driven by a 5 200 H.P. A.C. motor. The maximum rope speed is 3 000 F.P.M. 1.9/16 inches diameter non-spin ropes supported kibbles of 10 tons capacity. A 600 H.P. geared A.C. winder erected on the west side of the head frame, having 1-inch diameter non-spin ropes and a maximum wind speed of 1 500 F.P.M. was used to operate the service conveyances. A four-drum stage hoist driven by a 350 H.P. D.C. motor was erected adjacent to the service winder. It had 8 ft diameter drums accommodating 11 600 feet of 1.15/32 inches diameter non-spin rope per drum. The maximum speed at which the ropes were paid off the drum was 50 F.P.M. These ropes were coiled on the drums using a tensioning hoist so that all four ropes could be coiled under equal tension and all crossovers were matched by lining the drum flanges with plates. Because of this, the stage was maintained level throughout the wind, only minor adjustments through the clutches being necessary during the sinking.

The winding equipment for the sinking of the Main shaft was as follows: The north, center and south permanent winders were identical mechanically. The north and center winders had A.C. motors while the south winder had a 5 600 H.P. direct coupled D.C. motor with Ward-Leonard control. It had a maximum rope speed of 3 600 F.P.M. The center winder was used to operate kibbles of 14 tons capacity through 1.15/16 inches diameter non-spin ropes. The south winder was equipped with 1.1/8 inches diameter non-spin ropes and was used to operate the service conveyance. A stage hoist similar to that at the Ventilation shaft was sited on the south side of the headgear, the ropes being of the same size, length, and construction as those in use at the Ventilation shaft. (See Fig 3.)

4. MULTIPLE DECK STAGES

The stages were of similar design but differed in diameter. The stage in the Ventilation shaft was 20 feet in diameter; the stage in the Main shaft was 26 feet inches diameter. Each had nine decks, spaced 7 feet 6 in apart, except the second deck from the top, which was spaced 12 feet 6 in apart. The functions of the various decks were as follows:

Topdeck: to support the cross-head. stop blocks and give protection to persons working below.

Second deck: to accommodate the suspension sheaves.

Third deck: to carry cable baskets for lighting, blasting, and welding.

Fourth deck: to carry the trailing cable and eight hand-winches for raising and lowering the shuttering.

Fifth, Sixth and Seventh decks: to carry out walling operations.

Eighth deck: ~or setting the kerb ring, and to accommodate air and water distribution manifolds.

Bottom deck: to support the lashing unit shown in

Fixed decks. were preferred to a movable deck for walling operations as they allowed the pouring of concrete and the lowering of the shuttering to be done simultaneously.

The weight of the Ventilation shaft stage with 30 persons on It and with one ton of rock in the grab was 193 620 lb. The weight if the Main shaft stage with 40 persons on it and with the same weight of rock in the grab was 166 023 lb. The difference in the weights of the stages is because the large stage was of lighter construction and it supported a lighter type of lashing unit. The stages in both shafts were supported by eight ropes thus:

Four 1.15/32 inches diameter ropes pass over sheaves in the headgear, down the shaft, around four sheaves mounted on the second deck of the stage, back up the shaft and over the compensating sheaves. The compensating sheaves were mounted in the headgear on pivoted bearers, the free end of the bearers resting on electronic load cells that measured and recorded the loads supported at all times. The ends of the stage ropes were taken 2.5 turns in opposite directions around the compensating wheels and clamped off. (See Fig.5.)

5.      LASHING EQUIPMENT

The lashing equipment in the Ventilation shaft consisted of a piston or ram type unit which was used with a 20 cubic foot cactus grab. There was a 55 H.P. air motor auxiliary winch which served as a storage magazine for spare rope. The advantage of the ram type unit was that it had fewer moving parts and it required less maintenance, resulting in a minimum of breakdowns. It proved to be slightly faster than the winch-type unit since it could be lowered at high speed, allowing the grab to take a full bite. Its raising speed was approximately the same as that of the winch-type unit, provided that the air pressure was in excess of 100 P.S.I. Its disadvantage is it required air pressure of not less than 100 P.S.I. which necessitated the use of a booster compressor, it was about one and two-thirds times as heavy as the winch unit, and it required considerable maintenance of the mechanism. To keep the stage winding ropes within the limits of safety laid down in the Mines and Works Regulations it was not possible to use the ram type unit in the Main shaft, so a hoisting winch driven by an air motor was used. The air motor used was rated at 55 H.P. at 1 500 R.P.M. with an air pressure of 75 P.S.I. By increasing the governed speed of the motor to 2 200 R.P.M. and with a normal mine air pressure of 90 P.S.I. the motor developed approximately 72 H.P. which enabled the winch unit to operate at a slightly higher lifting speed than the ram unit. Complete winch units were kept in readiness on the surface in case of a major breakdown to an operating unit. Fortunately, this never occurred. The units were exchanged and overhauled after 100 hours of operation. A light storage drum with sufficient capacity for two spare ropes was fitted. (See Figs. 6 and 7.)

The load in the kibbles was tipped on to retractable chutes feeding into the headgear bin by the lazy chain method. (See Fig. 8.)

 6. SHAFT LINING

The procedure for lining the shafts with concrete was identical except that bunton pockets and two recesses for cables at right angles to the bunton pockets were additional features provided in the lining of the Main shaft. (See Fig. 9.)

The steel shuttering consisted of a curb-ring at the bottom, 2 feet 6 inches in height, sections five feet high, and a matching ring 2 feet 6 inches long at the top, making a total length of 30 feet. Openings were provided in the shuttering for attaching the boxes for the bunton pockets and the nut boxes when required.

 7. CONCRETE MIXING PLANT

Concrete for the shaft lining was mixed in the batching plants sited between the two shafts so that only a common sand and stone stockpile and common bins and cement silos were necessary. Five concrete mixers were mounted on a platform 12 feet above bank-level, two near the Ventilation shaft and three near the Main shaft. Sand and stone bins were erected

8 feet above this platform, the sand, and stone being scraped up a ramp into their respective bins from the stockpiles on the bank level. Three cement silos were erected over the platform. Weigh-batch cars were filled from the bins with a mixture consisting of 875 lb river sand, 1 025 lb t inch stone and 675 lb cement and were trammed to the mixers. The mixers were of the horizontal paddle type with a capacity of 30 cubic feet and were capable of giving a thorough mix in 30 seconds. 1.5 Gallons of 2 percent solution of calcium chloride and lissapol were added to each mix. The mixed concrete was fed via a launder into one of the two 6 inches pipes down the shaft to a kettle. From here it was distributed behind the shuttering by means of two hoses.

8. STRIPPING AND EQUIPPING THE SHAFTS

On completion of sinking operations in the Ventilation shaft, the shuttering was removed to the surface in sections. All the air, water, and ventilation pipes and brackets were removed from the shaft using the stage. The two 6 inches concrete pipes were left in place because it is proposed to utilize these for lining the sub-vertical shaft in the near future. On reaching the surface after completion of stripping the stage was dismantled. The concrete fan drift was then built over the shaft above the bank level. On completion of the Main shaft, everything was removed from the shaft working from the bottom upwards. The sinking stage was dismantled and removed from the shaft when it reached the surface and an equipping stage was then fitted. Two of the four-stage ropes were used to support the equipping stage. The ropes passed over additional compensating sheaves in the headgear so as to give four effective ropes to operate the stage. The equipping stage had three fixed decks are 15 feet centers to coincide with bunton spacing. The bottom deck was used for cleaning out bunton pockets, the second deck was used by the surveyors to establish the bracket positions and by the fitters to fix the guide brackets in the two recesses, and the top deck was used by the equipping crew for putting in position, lining up, leveling and grouting the streamlined bun tons. Skeleton conveyances were used in all six compartments. The bun tons were slung underneath the skeleton conveyances and the guides were suspended on crawl beams from the top of these conveyances. The steel bun tons were 14 inches by 6 inches and of the streamlined section. They were sandblasted, painted and checked on a jig prior to being sent down the shaft. This eliminated any alterations having to be made underground. The steel haft guides were of the top hat type, 6 inches by 4 inches and were exactly 29 feet 11 7/8 inches long. There was thus a 1/8th inch the gap at the joints between each guide. Holes for attaching the bunton cleats and the joint fishplates were drilled from a jig in which allowances were made for temperature variations. On completion of the equipping of the shaft, the stage was dismantled when at the shaft bottom and the sections were sent to surface.

9. VENTILATION DURING SINKING

The forcing system of ventilation was employed during the sinking, using two 30 inches columns in the Ventilation shaft and two 36 inch columns in the Main shaft. Canvas tubes sixty feet in length were attached to the ends of the ventilation columns so that the air could be discharged at a point not less than 80 feet from the bottom of the shaft. There were three 11 tons in fans at each shaft. Two of these fans were driven by 190 H.P. squirrel-cage motors and were rated at 22 000 C.F.M. at 29.3 in W.G. Standby diesel engines of 120 horsepower were provided to drive one fan at each shaft in the event of the failure of the E.S.C. power. The quantity of air supplied to each shaft bottom was never less than 31 000 C.F.M.

To ensure that the bank area remained clear of fumes, 22? inches diameter axial flow fans, arranged in parallel, were placed at sub-banks. These disposed of the exhaust fumes from the shaft through suitable ducts.

10. SINKING STATISTICS

Table I shows the personnel employed during the sinking of the Ventilation shaft. The Main shaft required an additional 68 Bantu giving a total of 677 persons.

The highest footage sunk in a calendar month was 1,251 feet. The highest footage sunk in 100 consecutive days was 3 311 feet. Altogether, 10 004 feet were sunk in 452 days.

The following figures are those for the month when the shaft was sunk 1 251 feet:

Average daily advance                 40 feet 5 inches

Rounds blasted                             147

Average advance per blast          7 feet 2 ? inches

Excavated diameter                     24 feet

Number of holes per round        130

Depth of holes                             8 feet

Number of machines                    30

Labour force                                 607

Percentage time lost                    6.73%

Table II shows how the sinking operations progressed and Table III shows the cost of the sinking operations.

11. PERMANENT LOADING ARRANGEMENTS

The loading arrangements are flexible because there are two 42 inches horizontal belt conveyors running parallel to one another under the reef and waste ore passes. A reef chute and a waste chute feed on to each belt. Limit-switches are provided on the operating mechanism of the door of each chute. These indicate to the banksman whenever there is a change over from reef to waste hoisting or vice versa. (See Fig. 10.) The belt conveyors di charge into inverted Y-shaped chutes. The four legs of these chutes feed into the four measuring flasks which are so arranged that they are directly opposite the skip compartments 1 and 2 on the north side and skip compartments 5 and 6 on the south side of the shaft. (See Fig. 11.)

There is a compressed air operated door in the crutch of the Inverted Y sections of the chutes to direct the rock to whichever side is required. The air cylinder operating this door is controlled by a solenoid pilot valve. The measuring flasks consist of four standard bottom discharged skip pans of 14 tons capacity at 20 cubic feet per ton, suspended in the standard bridles. These units are similar in every respect to those used for hoisting. The cross-heads of the bridles are supported on 8 inches diameter hydraulic rams. Pressure switches actuate the automatic weighing device. (See Fig 12.) The measuring flasks are opened by compressed air cylinders, one cylinder being mounted behind each flask. The flask discharge into the skip via a fixed chute. (See Fig 13. The flask is filled automatically, the cycle of operations being as follows:

When the empty skip arrives at the loading point in the shaft, it operates a magnetic switch that releases a locking device on the operating valve of the air cylinder. This enables the skipman or operator to open the valve to cause the contents of the flask to discharge into the skip. When this valve is released the cylinder exhausts and the flask returns to its closed position. A limit switch mounted on the back of the measuring flask and wired in scenes with the pressure switch of the hydraulic ram, forms a closed circuit to a relay which operates the solenoid valve of the air cylinder which operates the crutch door of the chute. When the crutch door is in the correct position for filling the empty flask, a series circuit is completed through the limit switch on the back of the measuring flask, the pressure switch and a limit switch actuated by the crutch door shaft and this allows the belt conveyor motor contactor to be operated. When the flask is filled to the predetermined load set on the pressure switch, the switch opens and causes the belt conveyor motor to stop. Schematrf diagrams of the loading operations and the electrical circuits are shown in Figs. 14 and 15.

12. CONCLUSION

I thank the Head Office and the Management of the Buffelsfontein Gold Mining Company Ltd. For permission to publish this paper and I also thank those who assisted in its compilation.

13. DISCUSSION

Mr. J. A. R. Alty (Associate Member): Mr. Casey's paper has particular merit in that it provides an uncomplicated precis of shaft sinking which will be of interest to those engineers who work outside this specialized field.

The rapid speed of sinking is most commendable and certainly, some parts of this can be attributed to the excellent pre-planning and the full use of models.

The design of the stages is a departure from the normal; they have nine decks and also appear to be heavy. Could Mr. Casey say to what extent such a large stage assisted in the rate of sinking?

It is of interest to note that two types of grabs were used. This would not at first appear to be an economical proposition as it increases the capital expenditure. However, a more detailed breakdown of the cost per ton or per foot advance, and the loading times, would materially assist in ascertaining the relative merits of the two types of units and would certainly, be of value in future assessment of which type of grab to use.

The maintenance costs of different types of lashing gear are always a subject for discussion amongst shaft sinking personnel and this would be an ideal, opportunity for Mr. Casey to give a detailed comparison of these two units with which he is familiar.

The use of chases for cables down the shaft is an unusual feature and will undoubtedly afford better protection to the cables.

It would appear that the bun tons were first lined up and then the guides attached to them. It will be of interest if the introductory paragraph from The Method of Bunton Installation of No. 3 Sub Main shaft, Western Deep Levels, by Mr. K. Richards, is quoted:

'In the past, the accuracy of guide installation was largely dependent on the accuracy with which bunton sets could be installed. Punch marks were established near the extremities of the bun tons, and direct measurements from plumb wire to these punch marks determined the positioning of the buntons. Guides were then installed and were accepted as being plumb. However, errors in fabrication and errors in actual measurement led to an accumulation of error which was in turn reflected in the accuracy of guide installation.

'This problem was overcome during the equipping of No.3 Sub Main Shaft, by reversing the order of activity, viz, by firstly plumbing the guides and then blocking and grouting the bunton sets from a plumbed set of guides.'

This method has proved successful and will surely become the accepted method of equipping a shaft.

If the air resistance presented by a standard R.S.J. bunton is taken as 100 percent, experiments have shown that the oval section or squashed pipe section bunton reduces this air resistance to approximately 45 percent, which is a great saving. However, by using a bunton of hexagonal section and of comparable strength, the air resistance can be reduced to about 28 percent. It would be appreciated if Mr. Casey would enumerate the factors which influenced the choice of section. Also, could he comment on a bunton spacing of 20 feet instead of 15 feet.

One of the most noticeable features of this paper is the particularly low cost of sinking and lining and one wonders if all of the numerous small costs Incurred prior to sinking, and also the normally hidden cast of workshop facilities, etc., were included in the figures given. For instance, mention is made of the extensive use of models and considerable pre-planning.

What was the cost of these items, and are they included in the price per foot of sinking?

14. AUTHOR'S REPLY

Mr. J. Casey (Associate Member): In reply to Mr. Alty. The stages were designed to be as light as possible, with due consideration of strength and safety. Their duty was to support all the equipment necessary for sinking, including personnel and to handle and place the shaft shuttering. This consisted of: A 2 ft 6 in high kerb ring at the bottom, five 5 ft intermediate sections and a 2 ft 6 in makeup piece at the top, having a total length of 30 feet in all. A long stage was thus necessary to handle the shuttering. This contributed considerably to the fast-sinking rate in that mining and walling operations could be carried out simultaneously.

The reasons for using the different types of lashing units in the shafts were more or less explained in the paper. The ram-type unit was approximately 65 percent heavier than the winch-type unit. With the bigger diameter stage and the heavier shuttering and because the weight of the suspending rope was more, we would not have been able to come within the factor of safety for the ropes as laid down by the Mines and Works Regulations when the shaft reached its ultimate depth unless this lighter unit was used.

Regarding the relative merits of the two units in cost per foot advanced, there was little difference in the relative costs of the two units, considering the greater amount of spoil to be removed from the larger diameter shaft. The maintenance costs on the winch-type unit were slightly higher, but this was offset by the higher costs of operating and maintaining booster compressors and higher grab maintenance on the ram type unit. The relative lashing speeds were approximately the same for both units after the rope speed of the winch-type unit had been increased by 40 percent.

Mr. Alty was apparently confused due to a printing error in the galley proof; the higher maintenance cost was on the cactus grab due to its high velocity when coming into contact with the spoil at the shaft bottom.

I would say in a shaft of 24 feet diameter or less, the ram type unit has a slight advantage in speed and costs. In a shaft greater than say 26 feet diameter, the winch-type unit has the advantage.

Mr. Alty is correct in his assumption that the buntons were first leveled, lined and grouted. The guide installation followed immediately.

A completely new method of lining up the buntons was devised by the mine Chief Surveyor. The guide cleats were jig welded on to the buntons prior to installation. The three bun tons forming a set were placed in the pockets in the shaft lining, spacer jigs were bolted to the guide cleats and the complete bunton set was lined up vertically and horizontally then grouted. It was not necessary to do any lining of the guides on checking the shaft after it was equipped, the guides were found to be within 1/16 inch vertically and there was even less variation on gauge over the total depth of the shaft. The average number of bunton sets and guides installed during the equipping period was thirteen sets per 24-hour cycle.

Regarding the bunton spacing of 15 feet, a great deal of consideration was given to increasing this to 20 feet during the design and planning stages of the shaft. The final design decided on is as shown in Fig. 11. It. will be noted that the guides are not all supported within the bunton frame; the two outer guides in Nos. 1 and 6 compartments are fixed by cleats and angle brackets bolted to the concrete lining in the cable chases. It was for this reason that a 15 feet bunton spacing was decided on.

The sinking costs are as tabulated in Table III, Cost of sinking operations. These costs do not include the costs of winders, headframes, compressor plant, and permanent electrical installations, but they do include all equipment necessary for sinking and equipping as well as maintenance of the equipment during the sinking of the shaft system. These costs do not include the construction of models and preplanning, which amounted to slightly less than R5.00 per foot. It should be noted that the sinking costs also include the costs of station cutting stations and lining them with concrete.