Vol 48 Iss. 1

When developing powerful steeply dipping seams with the division of the level into sublevels (for example, at hydro-mines), effective means of supporting the sublevel drifts are required. The support should provide reliable stability of drifts and ease of its installation - conditions for high rates of drifting by shearers or hydro-monitors. The type of such support depends primarily on the amount of rock pressure, which is the result of the distribution of stresses in the rock mass around the excavation.

One of the main obstacles to the introduction of mechanized supports in weak host rocks is the lack of data on the relationship between the magnitude of rock pressure exerted on the support and the area of the support. The present article is devoted to the determination of soil resistance to indentation depending on the diameter and material of a round die (metal or wood).

In clayey rocks under the action of a certain shear stress τ, creep deformations develop in time. At values of shear resistance τ less than some value τ∞, creep deformations have a damping character. When this value is exceeded, creep deformations do not damp out, and in plastic or frozen clay rocks their development in time leads to rock failure. The greater the magnitude of the shear stress, the earlier the clay rock fails.

General characteristics of clayey rocks. Lignite deposits of the Moscow Basin are located in complex engineering and geological conditions, without taking into account which mining and extraction works are extremely complicated. Among the phenomena causing difficulties in the development of the fields is the swelling of clayey rocks exposed by mine workings. Plastic clays are the most widespread among the clayey rocks of the coal-bearing horizon of the Moscow Basin. They are the main host rocks for coal deposits, composing their floor and roof, or forming intercoal interlayers.

In developing coal seams with the use of flexible floors and various kinds of shields, it is often necessary to correctly determine the lateral pressure of the backfill on vertical or inclined walls. Methods of determining the value of vertical pressure are mainly covered in the technical literature. Much less investigated is the lateral pressure, which can be considered as a consequence of thrust between pieces of rock under vertical load. Studies show that the state of the bulk material has a significant influence on the magnitude of lateral pressure. When the bulk material transitions from a stationary to a mobile state, the degree of its loosening increases and the value of lateral pressure increases significantly. Meanwhile, the known calculation formulas are built on the basis of schemes that provide a stationary equilibrium state of the granular material, so their use does not provide the correct solution in all cases.

Determination of mechanical properties of a rock mass in in situ conditions is a complicated and still unsolved problem. Therefore, when solving practical problems, indices of ultimate strength in uniaxial compression and tension, obtained by testing samples of these rocks taken from the most characteristic locations of the mass, are used as a characteristic of rock strength. However, this raises the question of the validity of extrapolating the results of laboratory tests from samples to rock masses.

Among the development systems used in Kuzbass on thick steep seams, the shield system is especially widespread. In this system, more than 40% of all preparatory workings are made up of coal chutes and traveling ways. Conditions for supporting these openings are one of the most important tasks.

During the current seven‑year period, the Tenteksky and Churubay‑Nurinsky coal districts are the main areas of construction of new mines in the Karaganda basin. Conditions of supporting horizontal and inclined mine workings at the mines under construction are as diverse as the physical and mechanical properties of rocks in which these workings are being driven. Supporting haulage workings of the Tenteksky district does not present great difficulties, as driving is carried out mainly in strong stable rocks. The most difficult conditions are for supporting mine workings of the Karadzharo‑Shakhansky section of the Churubay‑Nurinsky district, especially at the ventilation horizons. The supports installed here (timber lagging, steel, prefabricated reinforced concrete, etc.) are deformed under high all‑around pressure and must be replaced. Most of the workings were re‑supported several times during the construction period. Re‑supporting work requires large expenditures of labor, time and funds.

The combined chamber-lava system combines elements of the pillar and chamber systems. The system has the following characteristic features: the main roof is supported for a long time by specially left supporting pillars; to increase the bearing capacity of the immediate roof and to control the condition of the roof in the goaf, a light wooden support is installed, designed to support only the lower layer of the immediate roof with a thickness of no more than 4 m; the face of the chamber-lava, with a total length of up to 215 m, advances similarly to longwall extraction — in parallel cuts in one direction; the face area with a width of 3.4–3.8 m is not supported at all.

One of the urgent problems of further development of the Churubay‑Nurinsky district is the development of rational types of supports. Data on the manifestation of rock pressure in preparatory workings can be obtained by an approximate calculation method. It is necessary to determine the amount of load on the support of horizontal workings (in the conditions under consideration) depending on the physical and mechanical properties of rocks surrounding the workings, the size of the workings and the depth of its embedment from the surface, as well as the design of the support, i.e. the main factors that can be easily determined in production conditions. To solve this problem, the results of mine and laboratory studies, as well as the previously stated data are involved. In addition, the existing analytical calculation methods were used. The results of determining the value of vertical load according to these methods, as well as the results of direct measurements of the value of load P on the support with the help of dynamometers in the conditions of the ventilation horizon of mine No. 14 "Churubay‑Nurinskaya" are given in the table

Mining of steep seams in strips along the dip by shield complexes is a fundamentally new direction of mechanization of coal mining. The interaction of shield support with side rocks is poorly studied and is decisive in the design and selection of basic parameters of shield support.

The chamber-shield system with the use of mobile shields was proposed for the extraction of thick gentle seams. Production tests of such a system (1959) with the LG NK-1 shield confirmed the high efficiency and reliability of the mobile support of the protective type.

To reduce coal losses during hydraulic mining of thick steeply dipping seams by the sublevel hydraulic extraction system, flexible metal floors are used, separating coal from the caved rock and, along with completeness of extraction, allowing coal extraction to be carried out without support in the stope.

It is known that the anchorage strength of rod locks is one of the most important conditions for the performance of the rod support. Soviet and foreign researchers define the parameters of metal wedge‑slot rod locks differently. The use of such rods is considered expedient mainly in rocks of medium strength (with a coefficient of strength f according to M. M. Protodyakonov from 5 to 8) and to a lesser extent – in strong rocks (f from 8 to 12). However, to date there is no published methodology that is simple and convenient for practical calculations.

The correct choice of the direction of extraction largely determines the amount of bearing pressure on the pillars and the ore mass adjacent to the goaf, and the manifestations of bearing pressure determine the safety of extraction and the amount of ore losses. This factor becomes especially important in the development of fractured unstable ores. The Norilsk copper-nickel deposit develops mainly disseminated ores, which are mineralized gabbro-diabases. Some sections of the lower part of the ore body contain massive sulfide ores.

During the open-pit mining of the Tikhvin bauxite deposits, where production is expected to increase significantly in the near future, failures of the sides and outer dumps occur at a number of open-pit mines. At some mines (9, and to a lesser extent 6, 13 and 3) landslides and slumps significantly complicate the organization of work at the open pits and increase the cost of bauxite.