Table 1. Stages of application of drift supports in various combinations

LLC “West-Donbass Research and Production Center “Geomechanika” presents its innovative developments in the field of fastening of mine workings. The main direction is the scientific justification, the creation and industrial production of new high-resource constructions of metal supports and lock joints that ensure efficient and safe maintenance of mine workings in a wide range of mining and geological conditions for the development of coal and ore deposits.

World and domestic experience shows that the prospect of maintaining workings at great depths is associated with combined security systems, the main element is frame metal support (Table 1).

A retrospective analysis of the used means for fixing mine workings in the mines of Ukraine revealed a number of trends, such as an increase in sectional area and the density of the installation in the workings, use of heavier standard sizes of the mine special profile, which objectively reflects the inadequacy of the power characteristics of the types of arch supports used, lock joints and structural material for their manufacture.

If earlier the average sectional area of butt entries did not exceed 11.2 m2, at present it is 14-16 m2, and in deep mines – from 18 to 25 m2.

The second trend is the use of heavier standard sizes of rolling profiles for the manufacture of supports. Thus, the profiles of SVP-17, 19 went out of use and now only SVP-22, 27, 33 are used, and the last two are the most used ones. In total, this affected the negative increase (more than twice) in specific metal consumption of fastening the mine workings.

The concept aimed at increasing the bearing ability of the support by changing the shape of the section and the type of frame structure is a scientifically significant and promising one. It is based on the fundamental principles of rock mechanics, that the most stable form of the section is the ellipse (semi-ellipse), whose major axis is oriented in the direction of the main (largest) shifts of rocks.

In the transition to greater depths of development, there was a need for the new approach based on the priority of the serviceability parameter of the support (Q) and its characteristics – working resistance (Pp) and constructive pliability (Δ), owing to the unified physical nature of the process as the work providing formation of the “support – array” system: Q =Pp×∆. At the same time, the parameter of the extreme bearing ability of the support (Pп) is the determining factor for the possibility of increasing the working resistance (Pp) and the operability of constructure (Q).

Fig. 1. Influence of repulse of the support (P) on the shift of the rock contour U, U/r0 and the relative change in the section of the output ∆s/s
*Limit zone of blocking of adjacent rocks;
**Effective interval of power repulse of support.

We have proved the thesis that in order to radically improve the stability of mine workings, a comprehensive solution of the tasks aimed at the creation of new structures of fastening frames, lock joints and rolling profiles for the manufacture of supports is needed.

Researches show that the geomechanics of great depths is the interrelation of the physics of increased pressures and deformations of rocks. It has been established that extent of influence of really possible values of repulse of the support (P) on the value of final shifts of the output contour (U) is very significant, which is important and technically feasible for practice (Figure 1).

It is established that shifts of rocks can be slowed down or stopped by anticipatory increase in the internal boundary condition of the system of limiting equilibrium, corresponding to the increase in stresses, i.e. by the support reinforcement.

Due to the reason for the permissible shifts and the operationally acceptable flexibility of the support, its resistance should be selected within the range of 150-250 kN/m2 (while in typical arch supports 60-120 kN/m2), as the depth of mining is increased (H>1000 m), the effective interval P can be expanded up to 350-400 kN/m2, and more – is not appropriate.

As a basic support it is necessary to use frame constructions with increased values ​​of operating resistance (more than 350 kN/set) and constructive pliability (up to 700 mm for 3-link and up to 1000 mm and more for multilink models).

The supports of the new technical level (NTL) developed by us differ from the standard arch supports with the following features:

– change in the shape of the section of the support and the coupling of the bearing elements, depending on the lithological structure and bedding of the massif;

-the differentiated strength of the structural elements of the support at certain sites of the perimeter of the section, depending on the nature of the manifestations of the rock pressure and the prevailing deformation of rocks;

— change of a ratio of bend radiuses and the coupling of the forming segments, depending on the nature and the mode of loading of the support frame.

The supports of the first technical level include: tent ones – КШПУ-М, circular-linear ones – КЦЛ, polygonal ones – КПП, and the supports of the second technical level are: ovoid 2-radius – КМП-А3(А4)Р2, ovoid 3-radius – КМП-А3(А5)Р3 and circular-linear-ovoid – КЦЛО. All these supports are patented.

The main characteristics and parameters of the supports are given in Table 2.

Table 2. Main characteristics and parameters of the supports of new technical level

To ensure the high-quality production of NTL supports, a method for matrix pressing of the support elements has been developed and realized on an industrial scale at the plant WDRPC “Geomechanika”, which allows to perform productive bending of the forming segments of the required configuration and variable curvature, to minimize the length of the end sections of the bent segments and the deformation of the walls of the special profile providing stability of conditions of friction in pliability nodes.

Efficiency of supports of the new technical level (NTL)

Metal supports developed by WDRPC “Geomechanika” are adapted to the complicated mining and geological conditions: intensive rock pressure, large lowering of the roof and rock swelling, significant zones of destruction of the rocks of the contour massif, large asymmetric loads.

The analysis of the efficiency of the designed supports’ constructions is made on the basic parameters: bending moments in the section of loading efforts (Mimax), the coefficient of constructive quality

( );  the ultimate bearing ability (Рп) and the operating resistance (Pp); constructive pliability (Δ); working capacity (Q = Pp × Δ).

Supports of the new technical level have an improved and more evenly distributed bending moment diagram (Fig. 2).

Decrease in the values ​​of bending moments is: for NTL-1 supports – by 1,3-1,7 times; for NTL-2 supports – by 1.8-2.5 times. This is achieved by the degree of approximation of the geometric parameters of the section to the elliptical configuration: in standard supports, the deviation from ovality is 31-35%, in the NTL-1 supports – not more than 17%, and NTL-2 – less than 8%.

Fig. 2. The bending moment diagram (Мi) а – basic level support; b – NTL support

Shape changing of the frame structure of the support allows increasing the ultimate bearing ability by 30-35% for the NTL-1 supports and by 1.8-2 times for the NTL-2 supports without increasing the mass.

The account of the not uniform strength of the structural elements is achieved by changing the curvature of the forming segments and their associativity with the enclosing rock massif. It is established that with a decrease in the radius of the critical element, according to the hyperbolic law, the bearing ability of the support (Pп) increases, respectively, in proportion to the safety factor (Kз) – the working resistance Pp (Fig.3)

Fig. 3 Influence of the curvature of the segment bend on the bearing ability of the support

The overall comparative characteristic of the effectiveness of the developed NTL supports is given in Table 3.

Table 3. Comparative effectiveness of supports

Estimation of technical efficiency of NTL supports in comparable sections is represented by an integrated indicator of specific working capacity:

where Рр is the working resistance of the support, kN;
Δ – constructive pliability of the suport, mm;
m – weight of the support frame, kg.

A comparison of the effectiveness of the use of supports in comparable sections on the basis of the specific working capacity parameter is given in Table 4.

Table 4

Analysis of the data shows that the ovoid support is most effective. Stability of workings using ovoid supports is increased by 1.7-2.5 times for small sections; by 2,6-4 times for average sections and by 2,8-3,9 times for large sections.

NTL supports are characterized by the following advantages: without increase in weight, an increase in bearing ability (by 2-2.5 times) is achieved, which allows to increase (without decreasing margin of safety) the operating resistance of the frame (by 1.5-2 times) and to reduce the metal consumption of the fastening of workings.

Based on specific mining and geological conditions, the nature of deformation of rocks, and the manifestation of rock pressure, the following scheme for selecting NTL supports for specific mining and geological conditions is proposed (Table 5.).

Matrix for selecting the type of the fastening of mine workings Table 5

Fig. 4 Photo of supports of the new technical level

In total, we have developed 12 different constructions of the supports: tent ones (КШПУ-М), ovoid two-radius (КМП-АЗ(А4)Р2), ovoid three-radius (КМП-А3(А4,А5)Р3), circular-linear-ovoid (КЦЛО), circular linear (КЦЛ), polygonal (КПП), convex-triangular (КВТ, КВТ-2), ring (КМК), for cutting furnaces (АПКР), coupling supports (KC) and others (for photos see Figure 4).

With the use of NTL supports, a decrease in the metal consumption of workings (by 15-30%) has been achieved, an increase in the rate of their carrying out (by 10-25%), a decrease in volumes of delivery of rock mass (by 0.5-1.5 m3/rm), increase (by 2 and more times) between the repair period of maintenance of workings, reduction of total costs for maintenance of workings (from 30 to 70%). Supports of a new technical level ensure the stability of preparatory workings, which significantly reduces the costs of their maintenance, increases the productivity, safety and economy of mines.

The experience of large-scale application of NTL shows that the technical and economic efficiency of their application increases with increasing depth and complexity of mining and geological operating conditions.

Supports of WDRPC “Geomechanika” received a high appraisal of industrialists. Our permanent customers and partners are the mines of Ukraine. Experimental batches of supports have been tested in the mines of the Russian Federation, Bulgaria, Iran, Estonia.

WDRPC “Geomechanika” also provides specialized services: assessment of mining and geological and geomechanical conditions, selection of the most effective structures of NTL supports, organization of underground monitoring, justification and calculation of technical and economic efficiency.

  Dear partners! Our supports are unique and favorably different from those known for technical, quality and economic performance. WDRPC “Geomechanika” has a proper scientific and production potential and will satisfy the requirements of discerning customers.