The state of the art

Nevertheless, by 1959 it was concluded by the Bituminous Coal Association in America that some of the technical problems inherent in this conception were a long way from solution and a monitoring committee was established to observe and, if possible, assist in developments. It may be some indication of the slow rate of technological development, that despite the urgency of this project and the great financial returns that could accrue, it is only now (1987) that two units have been manufactured and are being tested underground in Australia. These units made by the Joy Manufacturing Company and Klockner-Becorit have every indication of being successful and if so will mark another major technological advance for the coal industry.

This will leave only one outstanding challenge to be overcome in the use of continuous miners; the cyclic securing of the roof as the machine progresses, which again introduces a down-time factor to its cutting operations. Although speeding up the bolting cycle has considerably reduced the delay caused by this operation, the complete cycle mining, conveying and roof support, has not yet been reduced to a non-stop operation.

When the electrical equipment in use for modern surveying is acceptable to underground mining the concept of total stations will be permissible, thus eliminating the standard practices of many years and rendering faster and more accurate results.

Open-cut and open-pit mining

Up till very recently the transport of material, either overburden or coal, from the working pit has been by wheeled transport, with large numbers of expensive units, mostly diesel powered and working to maximum permissable grades.

This method certainly achieves the maximum in flexibility but at a high cost, so that in-pit conveying is becoming more popular allied with in-pit crushing. However, these units have so far been restricted to normal conveying grades, say 18 degrees maximum.

The next steps being developed are conveyors designed to work much in excess of these grades with obvious advantages in space and adaptability.

Overall technological application in coal mines

Although technological advances have been perhaps directed in the main to the improvement of face productivity, and in that sphere have achieved the more dramatic results which receive attention and recognition, their effect has been felt over all facets of the industry.

Basic aims of mine planning

Returning to 1947, for instance, the colliery manager planning a new mine would have been confronted with a mine plan outlining the lease boundaries and little more, except for some surface contours and possibly seam contours derived from boreholes spaced about one and a half kilometres apart, and thus subject to considerable interpolation.

According to Jeffrey 'The basic aim of mine planning is to design mine layout and schedules that allow operations to be optimised, costs minimised and so the recovery of the resource maximised'. The mine planner of today, thanks to improvements in exploration techniques, has a substantial input technique included in his initial plan. Seismic surveys over the proposed development area will show the position of major faulting and intrusions and other geologically disturbed areas can be indicated that may call for further drilling.

The geotechnical testing of bore cores can reveal important information on rock types from the surface to the seam which indicate what strata are competent and to what extent; where fracturing exists; what rocks are susceptible to rapid breakdown on exposure and, among other things the most important of all, the likely behaviour of the mine roof under working conditions. Within the seam, in-seam seismic is in process of development to the stage where minor dislocations of the seam can be detected in front of the advancing face -a major consideration in longwall operations.

Australian Academy of Technological Sciences and Engineering