Vol 51 Iss. 1

November 13, 1965 marked 200 years since the founding of the oldest of the existing higher mining schools - Freiberg (GDR) Mining Academy. On this day in 1765 the project of the Academy foundation was approved, the educational work began in the spring of 1766. This anniversary attracts the attention of figures of mining science all over the world, as Freiberg Mining Academy until the middle of XVIII century prepared personnel for the mining industry of 50 countries ...

Tekeli lead-zinc ore deposit is a complex powerful steeply dipping lenticular deposit. The rocks of the hanging and lyingwalls are represented by strongly fractured, collapse-prone coal-clay shales with interlayers of dolomitized limestone and other sedimentary rocks. The ores are stronger and more stable than the host rocks and are represented by sulfides disseminated in coal-clay shales, quartzites and coal-quartz shales, as well as pyrite ores ...

According to the current temporary instruction, it is recommended to use rock bolting only in rocks of strength not lower than 3 (on the scale of M. M. Protodyakonov). According to preliminary calculations, the use of rock bolting in the drifts through thick coal seams, in particular, at the Kuzbass hydro-mines, should give a significant technical and economic effect. Since the coal strength factor of thick coal seams often does not exceed 0.3-0.5, and the coal mass is characterized by significant fracturing, it was necessary to justify the possibility of using rock bolting in difficult conditions. In this connection it was necessary to reveal the character of deformation of weak fractured coal near the mine workings, secured with rock bolts at different dip angles of seams ...

The anchorage strength of reinforced concrete bars depends on the type and mechanical properties of reinforcing bars and the strength of concrete. The question of the choice of reinforcement depending on its mechanical properties is covered in the literature quite fully, The strength characteristics of concrete used for reinforced concrete bars, have not been studied sufficiently ...

The nature of manifestations of mining pressure largely depends on the size of the cross-section of mine workings. As is known, in the same mining and geological conditions, maintenance of two-track workings is much more expensive than single-track workings. In this regard, in some basins of the Soviet Union in difficult mining and geological conditions prefer to drive two smaller cross-sectional workings instead of one large one. For example, in the Moscow sub-basin panel drifts should be double-tracked according to the conditions of mining technology, because almost the entire length consists of loading points. In the reverse order of mining the mine field, it is considered more favorable to sink panel drifts as single-track drifts with subsequent expansion to double-track drifts by the time of longwall face approach. The total costs are lower than when sinking two-track drifts at once. In the latter case, the cost of maintaining the workings increases sharply ...

A special place among the problems of rock pressure is occupied by the support and control of the roof in the stope. Domestic and foreign researchers have studied these issues on models and in mine conditions. In this case, the main importance was attached to the mining depth, the thickness and strength of coal and side rocks, the length of the face, the rate of advance of the face, as well as the choice of the type of support and roof control. Although many scientists and mining practitioners recognize the significant importance of the time factor and its impact on the reliability of the support, in research it is almost not taken into account. At shallow depths, with negligible mining pressure, the time factor and reliability do not play a significant role. With the mining depth, a significant increase in mining pressure leads to changes in the physical and mechanical properties of rocks. The tendency to heaving increases, their plasticity, creep and fluidity increase. These processes, as well as the processes of rock destruction, vary over time. Therefore, it is impossible to study mining processes without taking into account the time factor and its influence on the reliability of production schemes ...

The Maykhinskoye lignite deposit (in the southern part of Primorsky Krai) is a suite of 20 gently sloping seams, 7 of which have a mineable thickness of 1.3-15 meters. The dip angle of the seams is 2-10°. The seams occur at a depth of 30-350 meters. The host rocks are mudstones, siltstones and water-bearing sandstones. In the upper part of the coal-bearing strata, sub-basalt conglomerates are widespread ...

One of the directions for improvement of technical and economic indicators of coal mining in gently dipping seams is the wide introduction of the most progressive method of controlling mining pressure - the complete collapse of the roof with perfect types of mechanized supports, complexes, as well as complete and individual supports. However, as shown by research and experience of a number of domestic and foreign mines, the mining of seams which have strong, difficult-to-collapse rocks in the roof is very labor-intensive and far from safe (and under certain conditions, even inadmissible) process ...

Among the many factors affecting the behavior of the roof during extraction of coal seams, the macrostructure of rocks is of great importance. Patterns of side rock macrostructure on the manifestation of rock pressure in the mine workings have been little investigated ....

Sudden outbursts of coal and gas in working faces of single seams of Donetsk basin are currently prevented by drilling advance boreholes of large diameter. About 30% of faces of all outburst-hazardous seams of the central region of Donbass are developed with application of drilling advance boreholes as protective measures. The schemes of borehole location relative to the working face are different, and the spacing excludes outbursts. As is known, the mining pressure and the pressure of the gas contained in the coal are the main factors determining the occurrence and development of the outburst ...

One of the main ways to prevent sudden coal and gas emissions in longwall faces of single gently sloping seams is to weaken the coal mass with large-diameter advanced boreholes. These emissions in recent years in the mines of Donbass exceed 25% of all emissions. Despite the relevance of the method, until recently there has been no universally recognized methodology for determining the density of the protective network of wells. The radius of influence of wells is calculated according to the formulas of V. V. Khodot, A. V. Pavlov or according to the method of MacNII.

In the practice of construction and operation of mines, shafts and underground structures one of the urgent tasks is the calculation of pillars. Its solution is complicated by a variety of types of pillars and conditions of their operation. The nature of operation of inter-chamber pillars depends on a number of parameters, the most important of which, other things being equal, are: the structure of pillars, the properties of the rocks composing them, the mining depth , the type of links between pillars and the host rocks, the ratio of pillar sizes, etc.

In underground mining of potash and rock salts, as is known, room-and-pillar mining systems are widely used, providing high labor productivity and low cost of mineral extraction. However, losses in inter-chamber pillars in these systems reach 50% at domestic potash and salt mines. Mineral losses can be significantly reduced by reducing the width of inter-chamber pillars by filling the mined-out chambers with backfill. The most economically effective is hydraulic filling with waste from concentrating plants, as in this case the issue of dump placement is solved at the same time. It is also expedient to fill the mined-out space with backfill material specially extracted for this purpose (sand, gravel) ...

Wide coal pillars are considered to be interstorey and barrier pillars for various purposes, the width b of which is many times greater than the height m, and the length L significantly exceeds the width. In conditions of gentle bedding of seams such pillars under the action of active compressive load - the weight of overlying rocks - are subjected to crushing. The material of the exposed surfaces of the pillar is in a stressed state, which can be considered as flat compression in the first approximation. As one moves away from the outcrop planes into the depth of the pillar, the stress state changes to volume compression, and the horizontal stress component increases from the edges to the middle of the pillar. The nature of the stress state also varies with the height of the pillar: the horizontal component of stress decreases with distance from the contacts with the host rocks ...

When developing ore deposits in order to ensure the excavation of the richest part of the deposit in the first place or in case of simultaneous development by underground and open pit methods, it is often necessary to protect the overlying part of the deposit with artificial pillars made of concrete or combined pillars made of ore and concrete. The main purpose of such pillars, which determines the methodology of their calculation, is to ensure the stability of the overlying ore before its mining. A number of studies s are devoted to such calculations ...

The initial parameters in solving problems related to the manifestations of rock pressure are rock strength indicators. The main one is the compressive strength. As a rule, it is determined in the laboratory on samples of the rocks under study. There are also known production methods that allow determining the ultimate strength directly on the surface of rock outcrop (face, wall of excavation, roof) or at some distance from the excavation contour, in a borehole. However, these methods are imperfect, labor-intensive and complex ...

The Yar-Bishkadak field, which supplies brine to a number of chemical enterprises in Bashkiria, extracts a section of salt deposit with a thickness of 200-700 m, with the thickness of overlying rocks being 400-500 meters. Development is carried out by isolated chambers, which are created by salt leaching through wells drilled from the surface. The adopted technology - stepwise leaching - ensures the creation of chambers of approximately cylindrical shape with a diameter of 80-100 m and height at the end of mining equal to the thickness of the salt deposit (the height of individual chambers currently reaches 100-150 m) ....

With the development of theoretical and experimental studies, the general picture of manifestations of rock pressure, the mechanism of deformation and destruction of rocks in time and space, becomes increasingly clear. It is established that one of the main acting factors is not short-term, as previously thought, but long-term strength. The issues of stability, reliability of support of cleaning and preparatory workings and many others cannot be satisfactorily solved without taking this factor into account. Specificity of solving these issues (short life of many mine workings, changes in mining and geological conditions, etc.) makes it necessary to obtain the characteristics of long-term strength in the shortest possible time. The existing method of determining these characteristics with the help of special equipment during testing under constant load requires a long time (from several months to several years) and does not satisfy the necessary conditions ...

In the calculation of pillars, the study of stresses in the massif around unsupported excavations and in other similar problems is important to establish the value of the modulus of elasticity of rocks. When testing concrete, along with the determination of the modulus of elasticity under static loading on conventional testing machines, acoustic methods - pulse and resonance, allowing determination of the dynamic modulus of elasticity - are now widely developed. The pulse method consists in measuring the velocity of acoustic signal propagation. It is possible to determine the modulus of elasticity both in the sample and in the massif. In the resonant method, the natural frequency of the bending vibrations of the specimen is usually measured ...