Drifting at a modern Colliery
Sudamdih colliery had to undertake heavy drifting work because of the system of horizon mining involving nearly 12.5 km of roads in sand stone, shale and other coal measures. The drift in south cross cut at 400 m horizon was nearly horizontal and the drivage was done in the following manner.
(i) Excavated area - 4.8 m x 3.5 m
(ii) Completed area - 4.2 m x 3.1 m
The workers engaged on drifting were on the principle of "All men for all jobs." Normally a team of 8 workers per shift for a drift 4.2 m wide managed all the jobs, such as drilling, blasting, mucking, setting supports, extension of tracks, extension of ventilation and compressed air pipes, trailing cables, etc.
Drilling
At the face two airleg mounted jack hammers were in actual use; one drill was in reserve, and one was under maintenance at the surface. The weight of a drill was 25 kg with air consumption of 2.8 m3 of free air per min. at 6 kg/cm2. The air leg weighed 22 kg and had an effective feed length of 1300 mm. Flexible hoses were 25 mm bore for air and 19 mm bore for water (wet drilling). Hexagonal (22 mm) integral drill steels, 1.6 m long were used. The life of drill steel varied from 300 to 600 m. Four workers operated two drills and total 50 shotholes with 1.50 m effective length were drilled on wedge pattern.
Charging, stemming and firing
150-gramme cartridges of Ajax 'G' were used. Delay detonators with delays from No. 5 were employed and all the holes fired in a single-round using multi-shot exploder. The details on blasting are as below:
1. Size of the drift:
2. No. of holes drilled:
3. Charge per hole (Average)
4. Total charge per round:
5. No. of delays used:
6. Putt per round:
7. Surface area of the drift:
8. Volume of excavated rock in one round:
9. Tonnage of rock per round:
10. Rock yield per kg of explosive:
4.8 m x 3.5 m
50-55 approx.
600 g.
25-30 kg.
0 to 5
1.4 to 1.5 m.
16.8 m3
23.5 m3 (solid); 37.6 m3 broken
48 tonnes.
1.6 te approx.
The mechanical loader of overhead type moving on rails at the end of a temporary track was used. It unloaded into tubs of 1 m3 capacity. A small tugger haulage was used for hauling the empties inbye. The mechanical loader was compressed air operated consuming 5 m3 air/min. The compressor was installed at the surface and supplied air through flanged pipes of 150 mm bore, 6 m long pieces. Later on it was replaced by a portable compressor in the drift.
Support
Important excavations were lined with concrete blocks but the common arrangement in the drift was to support the roof by steel arches of 60 Ib. section rails. The steel arch was in two segments and foot plate 160 mm x 160 mm x 10 mm was welded to each segment. The two segments were joined by fish plates.
Ventilation
Ventilation was provided by an axial flow type auxiliary fan, capacity 270 m-Vmin, 7 kw power consumption, 95 mm w.g. Fans were installed in series at every 100 m intervals. The ventilation ducting was 1.5 mm thick M.S. sheets, 580 mm dia. in lengths of 3 m for ease of handling and transport.
Overall cycle time
On an average the time required by the composite face crew of 8 to complete one cycle .of advance of 1.4 m was approximately 17 hours; the break-up of this time into major operational groups is shown in the following table.
Operation
|
Elapsed time (Minutes)
|
1. Drilling — preparation, 50 nos. 1.5 m hole drilling, and mop up operation
|
200
|
2. Shotfiring — priming, charging, stemming, connecting up, walk out, fire, waiting for fumes to cSear, return to face, inspection and dressing:
|
120
|
3. Loading — preparation, loading out about 45 cars and cleaning up:
|
210
|
4. Setting supports — transporting arches, setting up and lagging:
|
260
|
5. Miscellaneous ancillary activities, shift change-over time, enforced idle time and other lost time —
|
230
|
Total cycle time:
|
1020 minutes
|
With the total cycle time of 17 hours, 35 cycles could be accomplished in 25 working days in a month and the monthly advance was about 50 metres.
Laser rays for drift drivage
For maintaining gradient and direction of drift, the theodolite is a reliable instrument in the hands of the surveyor. When driving a drift over a long distance, instruments based on laser rays have been used in some mines in recent years. At Zawar lead-zinc mines in Rajasthan, a tunnel 3.65 m x 3.05 m in cross-section, 2275 m long, with a gradient of 1:250 was driven using laser rays for alignment. The instrument known as Laser adjustment system, LAS, does not eliminate the use of theodolite, but replaces it to a great extent after initial use of theodolite in drift drivage.
Two target plates, called the first target plate and second target plate, are used in conjunction with laser instrument. The first target plate has cross marks but no hole in it. The second target plate has cross marks along with a small hole in the centre. The instrument can be fixed to the roof bolts or to the wall of the drift with the help of suitable brackets available from the manufacturers and nuts and bolts.
When driving the drift, the initial distance of about 10 m is driven by giving the alignment and gradient with the help of theodolite. Thereafter for installing the laser system on the brackets, the procedure is as follows:—
1) In the drift set a theodolite such that height of its telescope above ground level is nearly the same as the proposed laser system installation. Set the telescope of the theodolite in the desired direction.
2) fix the target plate (first target plate) away from the theodolite so that the centre of the target plate coincides with the centre of the cross hairs of the theodolite. To facilitate quick positioning the target plate is mounted on a suitable amount which can be fixed on wall/ roof of the 'drift,
3) Fix another target plate (second target plate with hole in the centre) on the wall/roof of the drift between the theodolite and the first target plate in such a way that the cross hairs of the theodolite, the hole of the second target plate and the centre of first target plate, all are in one line. Hence, the line through the centre of the two target plates is the required direction of alignment and gradient
4) Now replace the theodolite with the laser instrument and fix it on the wall/roof of the drift with the help of a bracket. The laser is switched on and so adjusted that the red beam of laser rays passes through the hole of second target plate and falls at the centre of the first target plate. In this position the laser beam follows the path of direction set by the theodolite,
Fig.7.13. Fixing up Laser instrument in a drift
As the drift advances only the first target plate is shifted from1 time to time and fixed on brackets in the wall/roof so that its centre1 Is in the line decided by the laser beam and the centre of second target plate.
Drivage or roads in metalliferous mines in rock/ore.
Level roads, drifts, drives or cross-cuts are driven in the same manner as described for drivage of stone drifts in a coal mine. Drivage of winzes is not a common practice owing to difficulties mainly of drainage, transport, etc. specially in steeply dipping veins. Drivage of raises is however a normal operation in every metalliferous mine. Raising operations have undergone much improvement over the conventional methods of raising by drilling-blasting-mucking. They have been mechanised to give fast progress with less manpower. The recent improvements include Alimak Raise Climber, Raise Bores (e.g. Atlas Copco Jarva, Robbins Raise Borer), etc. They are described in detail in 2nd volume of this series
Fig. 7.14. Jyoti Laser Alignment system Courtesy of Jyoti Ltd
Tunneling & road heading machines
The modern methods-of fast drivage of tunnels and roads in coal as well as soft rock like sandstone employ machines of which the following have proved popular in the Indian Mining Industry in recent years.
(1) 2000 DL of Atlas Copco Co.
(2) AM-50 Alpine Miner of Voest Alpine Co.
(3) Dintheader of Dosco Engineering Co.
Of these, the first two have been described in detail in Volume 3 of this series. Some of these machines are equipped with cutter chains and some others, with cutter booms. The earlier machines in the cutter boom category had only single booms, but machines with twin booms are also available in the market in recent years. The in-seam drivages are normally rectangular and ideally suited to all types of heading machines. In deep mines, however, the roadway supports are often steel arches. The arched profile generally needs a heading machine fitted with a boom. Such machines can cut the road for a desired profile of roadway.
The road header machines are capable of cutting rock which is not very hard, as well as coal.
Among the machines marketed by DOSCO Engineering Co., are the light duty, medium duty and heavy duty heading machines. The Road header MK 2A manufactured by DOSCO is a medium duty machine weighing only 23 te. The boom has axially rotating cutting heads. A lighter machine for road heading manufactured by DOSCO is known as Dint header and weighs nearly 17 te. The heavy duty machine is MK 3 having nearly 150 kW power. At Selby colliery of National Coal Board in UK, in a tunnel 4.2 m wide x 3.8 m high the average progress of heading with MK3 machine was 70 m per week (5-days week). The tunnel was completely lined by steel arches.
The Dint header has been used at Pathekhera Coal Mine of WCL. It has a cutting jib 1.72 m wide, i.e. in excess of the width of the machine. It weighs 16 te and exerts a ground, pressure of 0.124 MN/ m3. The tracks are hydraulically operated giving a working speed of 0.03 m/sec and a flitting speed of 0.14 m/sec.
The cutting cycle is started by sumping at floor level and then raising the jib to take the cut. The majority of coal is loaded down the cutter jib, any coal remaining being loaded on the return pass to the floor; Coal passes from the jib into the centrally mounted straplink hydraulically powered scraper conveyor to the secondary conveyor. This can be of two types; either a bridge belt conveyor with upto 16.0 m overlap or a short cantilever mounted swivel conveyor 3.2 m in length. The cutting action of the Dint header, being based on radially rotating picks, limits its application to coals and rocks of less than 600 kg/cm2 unconfined compressive strength; however, this is sufficient for the majority of coal seams and immediately adjacent associated strata.
The progress with a Dint header may be upto 10m/shift or 100 m/week.
Where the designed shape of roadway is square or rectangular, not more than 2.4 m in height, the Dint header is a suitable machine.
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