Candidate of technical sciences, associate professor Abdugalieva G.Yu.

The Republic of Kazakhstan, Almaty

RSE National Center for Integrated Mineral Recycling of the Republic of Kazakhstan

BSE Mining Institute after D.A. Kunaev

the technology of filling of open area at the development of flat coal seams

The filling of the open area is the most effective method of control of the state of the worked massive at the development of coal seams in the conditions of weak rocks.

Roof convergence is spread upward with the destruction of rock integrity in the form of stratification, the main part of which is formed in direct vicinity of the seam. The movement of the main roof and leaning layers result in formation of abutment pressure that leads to roof convergence in front of the longwall.

It is possible to reduce the roof convergence of the coal seam till the moment when it leans against the filling mass by means of the following activities:

- To form the filling mass right behind the protecting lining, moving together with the mechanized mining equipment;

- To exclude the incompleteness of the filling;

- To maintain high speed of wall advance.

These activities can be carried out most effectively in case of independence but interrelation of two technological processes: coal extraction and formation of the filling mass.

This set of activities will be effective only in the case when small part of rock over the seam is moved, without the layers of the main roof. If roof and leaning stratum convergence occurs, it will be impossible to stop this process and it will adversely affect the state of the seam roof. It is possible to attain temporary (during the development of one pillar) stability of the main roof by selecting the length of the longwall and by consistency of the development.

It is impossible to completely stop the roof convergence at least due to the shrinkage of the filling mass and the process will spread upward with rock stratification. To localize the process of movement, it is necessary to fill the inter-layer cavities and cracks of the worked massive. To implement the above-mentioned activities, we have developed the technology of backfilling of the open area [Patent RK №11612].

The width of extraction pillar (the length of the longwall) should not exceed the initial convergence interval of the main roof. In the middle of the extraction pillar, above the seam, the drift is done, from which the wells are drilled to supply the pulp with some addition of binding agent. As a backfilling material, ash or coal concentration waste can be used. With such chart, it is possible to fill the open area and to do tamping of inter-layer cavities and cracks at the height equal from the seam to the fill working. Falls and possible roof failures will serve as the material for partial filling of the open area and will not hinder the completeness of the filling, since it is done higher than the worked seam. The backfilling process can be done continuously and does not hinder the operation of the mining equipment that ensures higher speed of wall advance.

The wells for pulp supply are used for preliminary degassing of the coal seam and the fill working serves as gas drainage working during the whole period of development of the excavation pillar with the supply of outgoing air flow toward the worked area. The ventilation of the working area is realized in the same direction, i.e. the ventilation chart is direct-flow. Therefore, the working adjacent to the non-worked area is conserved or formed behind the longwall and serves for the development of the subsequent pillar.

The height of the developed seam till the fill working can be derived from the conditions of formation of natural arch. According to M. M. Protodyakonov, the height of the natural arch is calculated according to the relation:

, (1)

where x – is the half of the width of the working (outcrop), m;

f – is the coefficient of rigidity of the roof rock.

The width of the outcrop consists of the width of the working area supported behind the lining and of the distance from the lining of guard till the place of formation of roof rock support on the fill mass. Modern means of mechanization establish the width of the working area equal to 4,5-5,0 m. The distance from the lining of guard till the place of roof support on the fill mass depends on the distance between the well rings. Assuming that the radius of action of one well is 5 m, we will have the distance between the well rings (ℓ) of 10 m. Then the width of the outcrop will be 15 m.

For deep horizons, when the pressure on the edge part of the coal seam is higher than its breaking point at uniaxial compression, the estimated width of the outcrop is increased due to the zone of plastic deformation. Its value is changed depending on the depth of operations.

Then the formula for the calculation of the height of natural arch will be:

, (2)

where а – is the width of the zone of plastic deformation, m.

The analysis of the calculation data by the formula (2) showed that the height of the natural arch is changed from 4,8 to 5,9 m at the change of the depth of operation from 400 m to 1000 m. Therefore, the fill working made at the height of 6 m from the developed seam will not be affected by significant deformations.

To supply the pulp, the well rings are drilled from the fill working in such a number that the distance between the points of their intersection with the seam roof is 10 m. So, for 50 m long wall, the ring consists of 5 wells: one vertical and 4 inclined with the total length of 68 m.

The diameter of pulp lines is established depending on the possibility of the filling of the open area without the stoppage of the working area. So, at the speed of breakage face advance of 5 m/day, 50 m long wall and extracted thickness of 2 m, the volume of 500 m³ is produced. The productivity of the pulp lines with the diameter of 150 mm is 60 m³/hour. At the readiness coefficient of the pulp lines equal to 0,5, this volume of the open area can be filled in 17 hours. This means that in technological sense it is quite possible to ensure high speed of the breakage wall advance and the filling operations have much reserve of productivity.

As a result of the conducted studies, it is possible to make the following conclusions:

- The suggested method of roof control is technologically feasible at the modern level of development of mechanization of coal seam development;

- Geomechanical justification of parameters of the method is based on the regularities of movement and deformation of rocks of the worked massive;

- This method allows to exclude the adverse impact of development of the coal seams on the development drifts and facilities on the earth surface;

- The process flow sheet of operations allows the selection of the field of use of the method depending on the technical assignments and economic benefits by means of changing of the length of the longwall, place of the filling and parameters of the well fill.