Some Issues in the Development of Mine Fields with One-Sided and Two-Sided Extraction Fields

N. A. Fedorov

(Presented by the scientific seminar of the Department of the Development of Bedded Deposits, the Development of Ore Deposits, Mine Construction, Safety Engineering, and Mine Ventilation)

This article presents the results of a technical-and-economic comparison of methods for mining mine fields when they are divided into one-sided and two-sided extraction fields. On the basis of the technical-and-economic analysis, an attempt is made to establish the field of application of these preparation schemes for the average mining-and-geological conditions of Kuzbass.

Fig. 1. Development of extraction fields on the forward intermediate crosscut.

Fig. 2. Development of extraction fields in the direct course toward the rear intermediate crosscut.

One-sided extraction fields, as is known, may be mined toward the forward intermediate crosscut (Fig. 1) and toward the rear crosscut. Development of extraction fields toward the rear crosscut, in turn, has two variants: 1) work in the direct course, when preparation of the field and stoping proceed in the direction from the intermediate crosscut to the boundary of the extraction field (Fig. 2); 2) work in the reverse course, wh—

Preparatory workings are driven in the direction from the intermediate crosscut to the boundary of the extraction field, while extraction is carried out in the opposite direction (Fig. 3).

Fig. 3. Development of extraction fields by retreating to the rear intermediate crosscut.

The principal advantages of mining extraction fields toward the front intermediate crosscut are the following. The costs of maintaining haulage and ventilation seam drifts are small, since they are located in an undisturbed coal mass; it is possible to extract the interdistrict pillars, with the exception of protective pillars left above the intermediate crosscuts (in seams that do not require the leaving of fire-prevention pillars).

A disadvantage of working toward the front crosscut is the “overrun” of loads, as a result of which the costs of transporting the mineral increase, and in some cases also those of transporting stowing material.

When working in the forward direction toward the rear crosscut, there is no “overrun” of loads, but the costs of maintaining seam haulage and ventilation drifts increase, since they are located in the zone of the mined-out space, and coal losses increase because of the over-drift pillars and the pillars left at the boundaries of the extraction field. In addition, working in the forward direction toward the rear crosscut is inadmissible when developing actively self-igniting seams (especially thick ones).

The advantages of both variants can be obtained if extraction fields are worked by retreating to the rear crosscut. In this case the drifts will be maintained in an undisturbed coal mass, there will be no “overrun” of loads, and the need to leave protective pillars above the haulage drift is eliminated.

From the technical point of view, the development of one-sided extraction fields toward the front intermediate crosscut and by retreating toward the rear crosscut are practically equivalent. The development of extraction fields in the forward direction toward the rear crosscut cannot be used only with the shield system of mining and in the mining of self-igniting seams without stowing of the mined-out space. Therefore, the choice of a rational sequence for mining one-sided extraction fields must be made on the basis of an economic calculation.

The graph (Fig. 4) presents the results of an economic comparison of the indicated schemes for mining one-sided extraction fields for seams of medium thickness with an inclined floor-to-floor height of \(H = 200\) m and \(h = 300\) m. In the compared schemes, the following were taken into account: when working toward the front crosscut—additional costs for transporting loads; when working in the forward direction toward the rear crosscut—additional costs for maintaining haulage seam drifts in the zone of the mined-out space and the economic loss from coal losses in pillars at the haulage drift and at the boundaries of the extraction field.

...; when working in reverse advance to the rear crosscut—the cost of the coal lost in pillars at the boundaries of the extraction field.

It is evident from the graph that, when the distance between intermediate crosscuts is more than 200–250 m, the most economical of the variants considered is the working of extraction fields in reverse advance toward the rear crosscut.

If a mine field is worked in reverse advance, then the most economical arrangement will be to work toward the front intermediate crosscut.

In the Kuzbass, the division of mine fields into two-sided extraction fields is used fairly often (Fig. 5). Compared with one-sided fields, they have the following advantages: 1) the distance between intermediate crosscuts is increased, as a result of which the number of crosscuts (and sometimes also slopes) in the wing of the mine field is reduced and, consequently, the costs of driving them are lowered; 2) if necessary, the productivity of the extraction field and of the wing of the mine field can be considerably increased. But the division of mine fields into two-sided extraction fields has a number of substantial disadvantages: 1) because of the “overrun” of loads, the costs of transporting the mineral and stowing material increase; 2) coal losses in protective and inter-panel pillars increase; 3) technical difficulties arise in arranging curves and branch roads to the drifts; 4) ventilation of the mine workings becomes more complicated.

Fig. 4. Change in additional costs in the development of extraction fields toward the front and rear crosscut as a function of the distance between intermediate crosscuts: 1—toward the front intermediate crosscut; 2—in forward advance toward the rear intermediate crosscut; 3—in reverse advance toward the rear intermediate crosscut.

Fig. 5. Development of a mine field by two-sided extraction fields.

The indicated disadvantages are aggravated when a large number of seams (especially thick ones) are being developed and when the distance between them is small, since in that case it is necessary to drive, in one extraction field, in addition to the main ones, auxiliary intermediate crosscuts in order to facilitate the arrangement of branch roads to the drifts.

To establish the range of application of one-sided and two-sided extraction fields, we determined the expenditures associated with developing a suite of seams through one-sided and two-sided intermediate crosscuts for the average mining-and-geological conditions of seam occurrence in the Kuzbass. In the compared layouts the following were taken into account: 1) the cost of driving the group (field) drift and intermediate crosscuts; 2) additional costs for hauling the mineral (“overhaulage”); 3) the economic loss from coal losses in pillars. The results of the calculations are presented graphically in Fig. 6.

Fig. 6. Change in additional costs in developing a mine field by two-sided fields and one-sided extraction fields (retreating to the rear intermediate crosscut).

Analysis of the calculated data makes it possible to draw the following conclusions.

1. With intermediate crosscut lengths of up to 100–150 m, one-sided extraction fields up to 300 m long and two-sided fields up to 600 m long (the length of two-sided fields is twice that of one-sided fields) are practically equivalent in economic terms. With greater extraction-field lengths, the most economical are one-sided extraction fields mined by retreating to the rear intermediate crosscut.

2. With intermediate crosscut lengths of 300–400 m, one-sided fields 300 m long and two-sided fields 450 m long are economically equivalent. Increasing the length of two-sided fields to 600 m can provide some savings.

3. If the length of one-sided fields is taken as more than 300 m, then, with intermediate crosscut lengths up to 300 m, two-sided extraction fields will always be less economical than one-sided ones.

Thus, in group preparation of a suite of seams, the most rational in technical-and-economic terms is, with...

the use of one-sided extraction fields with their extraction in retreat toward the rear crosscut. Two-sided fields should be used only when the intermediate crosscuts are of great length (400 m and more) and the extraction fields are of great length (600 m and more).

LITERATURE

1. Teplinsky, G. A. On extraction fields and their dimensions in the development of closely spaced steeply dipping seams of the Kuzbass. Questions of the Development of Thick Seams (on the seventieth anniversary of Professor D. A. Strelnikov), Ugletekhizdat, 1953.

2. Shevyakov, L. D. Fundamentals of the Theory of Designing Coal Mines, Ugletekhizdat, 1950.