Vol 54, No 5 (2018)

Physical processes are initiated in rock mass by long-term induced vibration loads which give rise to triggering factors the neglect of which can result in instability of underground structures. The methodical characteristics of the trigger effect monitoring are described for the specific operating conditions of an underground powerhouse hall of a hydroelectric plant in the Kola Peninsula in Russia.

The main objective of this experimental work is to determine the physico-mechanical properties of tuffs used as building stone and to investigate the relationships between basic mechanical properties (compressive strength, flexural tensile strength, loss of volume by abrasion and impact strength) as well as physical and index properties (apparent porosity, dry unit weight, water absorption, P-wave velocity, Brinell hardness and point load index) of tuffs which are relatively easy to implement and low cost. The rock type investigated in this study was tuffs. Statistical analyses were performed to correlate the different properties. The results show that there are good and satisfactory relationships between the mechanical and physical-index properties of tuffs.

The influence of surface mining on the initiation of large seismic event is considered. The conditions of shearing-type dynamic events are described. A surface mine with the similar parameters as the Bachatsky open pit mine in Kuzbass is adduced as an example for quantifying the mining-induced change in the stress state in the plane of a future rupture as a result of an induced tectonic earthquake nearby a fault plane is quantified. The calculations are performed for different geometrical parameters of the fault zone: the changes are more observable in the zones of gently dipping thrust faulting and less appreciable in the area of steep normal faulting and strike-slip. In case of large surface mines, the zone of positive change in the Coulomb stresses higher than several tenths mega pascals has a considerable dimension and an area markedly larger than the area of nucleation zone of earthquakes of the magnitude M ≤ 6. In such conditions, even a small variability at the level of first percentage points of the natural stresses can be sufficient for the initiation of seismicity-generating shearing along the high-stress faults. It is found that, as against underground mining, the surface mining activities have no influence on localization of large earthquake sources but can draw the event nearer.

Practice of rock drilling with tricone roller bits, which are extensively used in surface mines, needs proper modes of descriptive statistics for predicting the failure rates of its different sub-assembled components. The statistical models for drilling with tricone roller bits are investigated in this article and probability of the non-failure operation is calculated. The interdependency of different component failures is examined by 3D contour plot. The failure rate of the components observed is found not significantly different at 95% contour. In such condition, the reliability is best modelled by Mixed Weibull technique.

Intersector models are efficient mathematical and modeling tools, which are well studied and widely used in economy. It is contradictory that intersector analysis is neglected in mining, especially since no other field has accepted and implemented the application of the model of operation research as mining did. There are not many satisfactory explanations as to why this is so. In order to explain this dilemma, this paper is directed at the peculiarities and characteristics of the intersector analysis, towards observation of its application in the mining industry on the intersector model of the Mining basin of Kolubara, which operates in the system of the Electric Power Industry of Serbia, and demonstrates the implementation and validation of observations and conclusions.

Longwall top coal caving mining provides high productivity where thick coal seams exist. The study aims to predict the cavability character of the top coal for deep and thick coal seam in Soma lignite basin located at Western Turkey. Active longwall top coal caving mines are at a depth of 100–400 m and they were used for comparison purposes. New coal mining operations will be initiated in deep sectors of the basin in the future. Future longwall top coal caving operations will be unique under a depth of 700–1200 m with a varied thickness. Several empirical and numerical methods are utilized in the study. Pre-existing empirical approaches lack of essential data and additional numerical modeling is necessary to be employed in order to assess cavability character of the projected new mines. Numerical modeling provides a practical platform for construction of ground response curves. Existing mines and future mining operations can be evaluated and compared by ground reaction curves and a final conclusion about cavability character is reached.

Airflow reverse is a severe problem in an underground ventilation system. In addition, the airflow stability and safety production can be seriously affected by the problem of air velocity overrun in the roadways. In this study the crucial causes of the ventilation problems in a coal mine case study are analyzed and a solution is proposed through an analytical methodology. Measurements indicate high air resistance in the shaft and low values in the maintenance roadway, generating abnormal airflow directional behaviors. Strategies to solve the ventilation-related problems have been proposed and implemented, verifying normal ventilation conditions.

The influence of structural characteristics and interaction parameters of minerals on separation method of lead-bearing complex ore in Russia is analyzed. Based on the studies of deep dissociation of minerals under disintegration using Mineral Liberation Analyzer (MLA), the quantitative distribution of mineral associations in grain-size categories is determined. From the data on mineral dissociation, the series of mineral associations, characteristic of complex ore from some deposits, are defined using milled samples of ore material. It is shown that galena associations with chalcopyrite, fahlore, secondary copper sulphides, sphalerite, pyrite and gangue mostly occur in finely dispersed aggregates with fahlore and, to a lesser degree, with other sulphides. The obtained series of mineral associations make it possible to determine the sequence of dissociation and separation of final-size minerals in the inter-cycle operations during flotation. The primary flotation concentrate contains fahlore, secondary copper sulphides, gold associations, galena and corroded pyrite.

The influence of the velocity and time of pyrite slurry stirring on the kinetics of air bubble mineralization is studied. The subject of the research was pyrite of −0.074+0 mm in size, and the collecting agent was sodium ethyl xanthate. The influence of the velocity and time of pyrite slurry stirring on the mineralization kinetics of air bubble is assessed. The conditions, hydrodynamic modes and time of pyrite slurry stirring to provide minimum and maximum areas of air bubble mineralization at the constant concentration of sodium ethyl xanthate are determined.

The purposeful formation of man-made deposits is connected with the creation of such conditions under which a waste material acquires preset process properties while stored. This will enable future environmental clean processing of waste. Aiming to determine general mechanisms of formation of process properties in copper-pyrite ore tailings, the comprehensive analysis of mineralogical composition of tailings from three concentration plants processing ore from six large copper-pyrite deposits in the South Ural was performed. The crystal-chemical formulas of the basic ore minerals are studied and systematized. The morphological varieties of ore minerals are identified. It is found that even in case of deposits of the same genetic type, processing regimes and parameters of current mill tailings depend on the initial mineralogical features of waste based on which man-made deposits are formed. These features have influence on the mechanisms and stages of the secondary minerogenesis in the man-made deposits.

The test bench and procedure are proposed for investigating intensification of methane release from coal samples under wave field action, which favors increase in degassing rate. The additional equipment is designed for delivering coal cores from mines and taking into account free-released methane volume.