Vol 61 Iss. 1

Mining engineer, Professor Dmitry F. Borisov for fourteen years, from 1954 to 1968 headed one of the leading departments of the Leningrad Mining Institute - the Department of Reservoir Deposits Development.

Chamber systems of development with solidifying backfill are becoming more and more widespread. This causes the need for further development of calculation methods for determining the basic parameters of the systems and strength properties of the backfill. The purpose of such calculations is a reasonable choice of the width of inter-chamber pillars, chamber spans, width of a panel or block, dimensions of inter-block (panel! pillars, determination of the required strength of artificial pillars. The results of calculations, of course, will be different depending on the order of development of sections (blocks), chambers within one block, the structure and properties of the filling massif and other conditions.

The problem of development of thick steep seams with backfilling has become especially acute in Kuzbass, where due to a number of circumstances of technical nature it is required to significantly expand its use, while coal mining with backfilling is developing here very slowly. The unpopularity of backfilling in Kuzbass is explained, first of all, by the low efficiency of the mining systems used there. Thus, excavation of thick steep seams with backfilling is still carried out by the old systems, with division into layers.

The development of potash beds is complicated by sudden salt and gas emissions. Such emissions are observed in the USSR during the development of Verkhnekamskoe and Starobinsky potash deposits.

At domestic brine fields deposits of rock salt of various thickness (from 40 to 700 m) and depth (from 300 to 1400 m) are developed by underground dissolution, through wells. As a rule, cylindrical chambers of 100 m diameter are used. The chambers are arranged on a 200x200 m grid, and the width of inter-chamber pillars is 100 m. Such sizes of pillars are insufficiently justified due to limited experience of underground dissolution and lack of tested solutions. As a result, there is a danger of pillars destruction and surface shifts.

At the Yar-Bishkadak field the rock salt deposit with the thickness of 200-700 m and the thickness of covering rocks of 500-600 m is developed by underground dissolution through wells from the surface. The development is carried out by individual vertical chambers, the diameter of which, according to the project, is equal to 100 meters. Due to untimely control of erosion results, there are deviations from the project, sometimes the diameters of the chambers reach 160-190 m, so it is not clear how much the actual outcrops of excavations meet the requirements of stability. The current absence of surface shifts and large outcrops in the chambers associated with the cessation of operation of wells is not yet a sufficient guarantee of the safety of further development, as the duration of operation of the chambers (3-15 years) is short compared to their total service life (50-80 years). As a result, there is a need to predict the stability of rocks and determine the maximum allowable spans of brine excavations.

Employees of the Leningrad Mining Institute together with workers of the mine № 1/2 of the trust “Uglegorskugol” in 1967-1968 conducted at the mine observations of the manifestations of rock pressure at different methods of excavation and roof management. The purpose of the observations was to improve the technology of excavation of semi-decaying layer VI and to choose the most rational method of roof management. Formation VI is relatively sustained, the excavated thickness is 0.95-1.10 l, the dip angle is 8-15° The roof of the formation is represented by layered mudstones (0.4-0.6 m) and dense fine-grained sandstones (15-20 m). The stratum is underlain by argillites (0.1 m) and siltstones of medium strength, up to 8-10 m thick.

Joint efforts of the staff of the Leningrad Mining Institute and the Sakhalinugol combine in 1967-1968 conducted numerous mine and laboratory studies aimed at improving the development systems, mechanization of cleaning works and roof management of thick layers of hollow dip.

In the development of thin and medium-power steeply dipping seams systems with long cleaning faces on the dip the most labor-intensive and heavy is the fastening of bottom-hole space, which takes up to 55-60% of working time.

Significant spread in both coal and ore industry are shield and flexible slabs, for the choice of rational and reliable designs of which it is necessary to know the loads acting on them.

The methodology and results of laboratory studies of the process of collapse of overlying rocks are outlined. The researches are executed in the Leningrad Mining Institute for conditions of development of apatite deposits of Khibiny, hanging side of which is represented by strong fractured rocks.

The magnitude of rock outcrops, the load on the support of mine workings, and the displacement of their contours are determined mainly by the size of the inelastic deformation area formed in the rock mass surrounding the workings. In the practice of maintenance, the majority of preparatory mine workings are influenced by the support pressure, and there are no calculated methods for assessing this effect on the size of the area of inelastic deformations.

In the practice of maintenance of mine workings there are often cases of their mutual influence. Especially significant impact on the stress state in the vicinity of the preparatory workings. The solutions of these problems are complicated and cumbersome, therefore they are mainly performed for cases of mutual influence of excavations of the same shape. Only some solutions for different shapes are known. However, these solutions due to the complexity of the finite formulas have not been widely used to determine the stresses in the vicinity of the excavations. It is necessary to create simpler methods of calculation.

When studying the manifestations of rock pressure on flat and volumetric models, various types of dynamometers are now widely used to create elastic measuring bases of stands.

Violation of the solidity of the massif, associated with the development of deposits, is accompanied by a number of physical processes Rocks in the zone of influence of mine workings are in a stress-strain state, which is a complex function of the structure of the massif and mining conditions of field development.

The steady increase in coal production and the transition to the development of new deposits with increasingly complex conditions of occurrence makes the problems of control over the manifestations of rock pressure and prediction of the behavior of the roof in the mine workings of the mines of paramount importance, which has not yet found its solution. This is due to a number of reasons, in particular, insufficient study of the processes of rock pressure, the lack of a methodology for systematic prediction on the basis of control measurements of the state of the massif.

At the Department of Construction of Mining Enterprises LGI developed a method of stress measurement, instruments and apparatus, which are characterized by simplicity, reliability and sufficient accuracy. The method is based on the assumption that if a sensor is placed in a borehole in a mountain massif, providing it with a good enough contact with the walls of the borehole, then as a result of the movement of the walls of the borehole under the action of the load, the sensor readings will simultaneously change. The forces acting on the sensor will decrease or increase depending on the location of the rock mass under compressive or tensile stresses.

Physical and mechanical properties of salt rocks were investigated in laboratory and mine conditions in relation to the problems of rock mechanics-calculation of rational parameters of the chamber system of development and identification of regularities of manifestations of rock pressure. These tasks are of great importance in the development of Starobinsky potassium salt deposit, represented by several potassium beds, occurring at a depth of 420-640 meters from the surface. Two potash beds with thicknesses of 1.8-4.0 m and 4.5-7.0 m, occurring respectively at a depth of 420 and 580 m, are being developed at the deposit.

Along with the development and improvement of traditional methods of pressure determination, based on the study of elastic deformation values of rocks, various physical methods are increasingly used, including gamma methods of determining the density of rocks.

In general, geologically complicated areas of reservoir deposits represent zones of disturbances that differ slightly in electrical properties from the well-conducting surrounding rocks. To study the disturbances located in a highly conductive medium and at rather large (up to 200 m) distances from the source of electromagnetic waves, rather low frequencies are required, and it is often impossible to use the usual methods of interpretation of the results of radio-wave scanning.