Vol 64 Iss. 1

The Department of Construction of Mining Enterprises (CME) at the Leningrad Mining Institute was established in 1947. Its head from the time of its establishment to the present is Professor B. V. Bokii. At first he was the only teacher at the department and taught all special mining disciplines for the specialty "Construction of Mining Enterprises" and the course "Driving and Supporting of Mine Workings" for the specialty "Development of Bedded Deposits".

The activity of the St. Petersburg Mining Institute from the first years of its existence was characterized by a close connection with production. A natural consequence of this was the participation of its graduates and professors in the creation of the coal industry of the Donbass, which developed and deepened as this industry developed.

To determine the place of rational location of field development workings, the choice of type of support, establishing technical conditions for its design and solving other practical problems, it is necessary to assess the stress state of the rock mass near these workings.

The stability of a mine working is mainly determined by the size of the zone of inelastic deformations formed in its vicinity. This zone can be found by calculation.

Rock outbursts sharply reduce the rate and significantly increase the cost of driving workings, and create unfavorable conditions for mining operations at shafts under construction.

Sedimentary rocks usually have a layered structure, and the strength characteristics at the contacts of layers (cohesion cₖ and angle of internal friction φₖ) can vary from zero to their values in the material of the layer (cₘ and φₘ).

At present, the development of minerals is carried out and designed at great depths. Practice shows that at depths of about 800 m the stability of mine workings significantly deteriorates. To predict their stability, it is necessary to comprehensively investigate the physical and mechanical properties of rocks, especially their rheological properties, for example, stress relaxation.

At present, considerable experience in experimental and theoretical studies of stress distribution around workings of different cross-sectional shape has been accumulated. Most of these studies have been carried out with reference to workings with a smooth contour; however, it is known that the drilling and blasting method of sinking produces an irregular contour of the working. The technological irregularities formed in this process, as well as rock falls occurring in some cases, cause a redistribution of stresses with the formation of zones of increased stress concentration. Under field conditions it is difficult to determine the magnitude of stress concentration in these zones. Therefore, studies are usually carried out on models.

Practice shows that in ore mines, where mass explosions are used for stripping of useful minerals, the maintenance of mine workings causes significant difficulties, which increase with increasing depth of development.

Structural weakening of rocks is currently studied in various aspects. The diversity of the resulting tasks determines a large number of research methods. Most of them provide only an indirect assessment of the weakening of the rock mass and do not give quantitative relationships for the influence of rock weakening on their strength and deformation characteristics under conditions of natural occurrence.

The reliability level of a support or its part is determined by the numerical value of one or more reliability criteria, for example, the mean time between failures, or the probability of failure-free operation over a certain period of time.

Annular and arch supports subjected to loads may fail either from insufficient strength or from insufficient stability, which is checked by determining the critical load causing loss of stability of the structure.

The stability of mine workings depends to a large extent on the shape of their cross-section and the corresponding outline of the support. However, this well-known principle is often not taken into account, as a result of which the load-bearing capacity of the support is not fully utilized.

A four-hinged support is a statically determinate geometrically variable system with one degree of freedom. In surface structures, geometrically variable systems are almost never used because of their instability. Therefore, structural mechanics does not provide a specific methodology for their design.

For efficient operation of metal anchor rods, they are given an initial tension of about 3–4 t. Reinforced concrete solid rods are usually installed without initial tension; moreover, they work no less effectively than metal anchor rods. Steel-polymer rods with a plug lock are installed both with and without tension

From flooded workings, a regulated release of water with a large hydrostatic head can be ensured by reliably determining the size of the pillar left between the flooded working and the face of the crosscut, along which the water is planned to be discharged. To calculate the size of the pillar, it is necessary to know the compressive strength of rocks, which is usually determined on samples at natural moisture content.

It is known that rock in the sides of horizontal workings is destroyed either by shear along one or another sliding surface or by detachment of the near-contour zones of the rock mass along vertical surfaces. Failure by shear is well explained from the standpoint of the theory of limit equilibrium of a cohesionless medium. The second possible type of failure — detachment of near-contour zones — has so far no clear explanation.