Determining the gas-transfer index of coal is investigated on the basis of the operation of the PGO-1 laboratory instrument. Its operating principles and construction are briefly described as is the method of measurement of the gas-transfer index. This method of measurement is determined in three successive operations, through use of a vacuum pump to remove all methane and air from the surface, through saturation of the coal with methane to a near-equilibriums state at atmospheric pressure, and through liberation of methane from the coal into the empty space of the instrument with pressure measurement. It is shown that the gas-transfer index of coal is determined not only by the kinetic parameters of desorption but also by the technology used in measuring this index which is described by the mathematical model developed here for the pressure rise in a closed volume on account of the desorbed gas.

The authors attempt to develop a general method for predicting the danger of ejection from coal beds at the point of opening, regardless of the geography of the coal deposit. The authors determine that this method may consist of the following stages: determining the consistency coefficients for the given coal field; measuring the gas pressure at the point of opening of the bed; determining the strength coefficient of the coal by the comminution method from a core sample taken at the point of opening; determining the mean distance between cracks, the crack volume of the coal, and the gas permeability from the coal sample taken and calculating the parameters shown.

The authors derive an analytic expression for the maximum efficiency of an electromagnetic drive for which the inductance varies according to a hyperbolic law and they determine the conditions under which it is achieved.The equations for hammers, stamps, pumps, tampers, vibrator agitators, and other machines with an electromagnetic drive are shown. It is shown that at the initial instant the armature of an electromagnetic hammer with a drive of optimal efficiency should have the initial velocity 2.7 m/sec. As time passes, all the dynamic characteristics vary according to a parabola while the current in the magnetizing winding remains constant.

In conclusion, the author thanks Academician E. I. Shemyakin for the valuable instruction given in his discussion of the study.

The authors construct a mathematical model describing the stress distribution arising from underground mining operations in coal and rock mass which incorporates heterogeneities of the mass such as in inclusions and pressure differentials along with potential energy accumulation owing to pressure and deformation attributable to mining activity and strategy.

Most rock beds have a block structure formed by natural cracks. The principles of description of the crack-structured disruptions of rocks for prediction of mining exposure stability and for developing the principles of support structures have been discussed. Most of these studies, however, have disregarded the tectonic stresses which affect the natural stressed state of the rock. The present study responds to a practical need of evaluating the combined action of cracks and tectonic stresses in rocks as they affect the loss of stability in large-span horizontal exposures in mines; a seismic method for predicting exposure stability is developed on this basis. the study was done for mines of the Kola Peninsula.

1. As a result of generalizing the experimental data, it is shown to be possible to select the initial volume Vo as the index of the type of hose and the relative change in volume V as the pliability index. 2. With the chosen indices V0 and V, linearization of the elastic characteristic of hydraulic connectors by means of Eqs. (7) and (8) is possible with an error not exceeding 1.5%; this significantly simplifies the calculations. 3. The recommendation for more accurate calculations is to measure the actual volume or use Eq. (6) under the condition of measuring the actual length of the hose. 4. In special cases, where it is necessary to take account of the initial nonlinear section of the characteristics, Eq. (5) may be recommended.

A mathematical model of a pneumatic rotary drill is described which incorporates the pneumatic and thermodynamic parameters of the drill into a design optimization formulation from the standpoint of rock drilling in the mining industry.