Improvement of load-bearing capacity of arched support using rolled steel reinforcement in mines

The economic efficiency of coal mining at the reduced cost is directly related with maintenance of operation conditions in temporary roadways. This article proposes a method of increasing the loadbearing capacity of the three-link arched support made of a special rolled profile (SRP) by increasing the stiffness moments of arched support sections subjected to the greatest bending moments. It is determined to be necessary to install the same size SPR in the support sections exposed to the greatest bending moments. Mathematical modeling of the reinforcement shows that the sufficient length of SRP segments is 30 cm. The calculations show that SRP 27 is replaceable by SRP 17 with the same size inserts, which allows saving of 10 kg of steel per each meter of the arched support. The proposed method of increasing the load-bearing capacity of the support will reduce the specific content of steel in the mine support manufacture and, thereby, will enable significant saving of material and labor resources. The studies conducted to substantiate the proposed solution include: determination of bending moments and normal forces in the three-link steel arched support by the computer-aided procedure of VNIMI (All Union Research Institute of Mining Geomechanics and Mine Surveying) for the specific existing conditions, with the subsequent choice of the required size of the support; stress–strain analysis of rock mass and mine support in ANSYS environment; economic calculation of the proposed solution effectiveness. The implemented researches give grounds to believe that the proposed variant of increasing the loadbearing capacity of the support made of the rolled steel profile can significantly improve stability of mine roadways. It is possible to strengthen the support without reducing the metal content in cases of expected deformation of the support under the influence of the confining pressure, when the other methods of maintenance-free support in roadways are ineffective or require a lot of time, materials and labor.

FEATURES OF STRESS-STRAIN STATE OF MINE SUPPORT WHEN FILLING ROCK FALLS WITH PHENOLIC RESINS

The problem of finding the stress-strain state of the mine support and surrounding rocks when filling the voids with phenolic resins has been formulated and its mathematical modeling has been carried out. The pattern of distribution of stress fields in mine support and rock mass and their change depending on the geometric dimensions of the area filled with phenolic resins have been determined under various boundary conditions. It is shown that the use of phenol resins contributes to an increase in mine support stability, which allows using the developed technology for the elimination of rock caving in different mining and geological conditions. The calculation results have been discussed.

Application of Numerical and Block Geomechanical Modelling to Determine Parameters of Large-Section Chambers

The study is exemplified by complex workings of a main ore pass that include a variety of underground structures, usually with unique dimensions which depend on the function and size of the equipment placed. The technical solutions for the underground crushing plant and associated structures envisage construction of chambers with the height of up to 35 m and the width of up to 20 m at the depths exceeding 800-1000 m. Such conditions call for a closer attention to be paid to the mine support parameters, especially the bolting depth. A block geomechanical model was designed in the Micromine Mining Software for the rock mass of the new main ore pass. Geotechnical boreholes logs and results of physical and mechanical rock tests were used as the input data for the model. Four domains were identified in the block geomechanical model for subsequent numerical modelling. A 3D model of the stress-and-strain state of the rock mass was made using the CAE Fidesys software based on the Micromine wire-frame model of the main ore pass. The history of the rock mass incremental loading was reconstructed for correct simulation of its stress-and-strain state. Prior to the excavation, the rock mass is pre-stressed by the weight of the rock strata. The excavation phase was then simulated in the stepwise manner. An array of points with the values of maximum principal stresses was downloaded from the numerical model post-processing program and interpolated into the block geomechanical model to refine the SRF parameter of the Barton's Q rating. Based on the obtained Q values, the mine support parameters for chambers were determined using the Barton, Hutchinson and Potvin empirical methods.

Experimental Study on Dynamic Mechanical Properties of Coal Gangue Concrete

In order to study the static and dynamic mechanical characteristics of the coal gangue concrete used in the mine support structure, the compressive strength test, the drop weight impact test, and the Split Hopkinson Pressure Bar (SHPB) test were conducted. The compressive strength, initial and final impacting energy, dynamic strength, and failure characteristic of concrete were obtained of the concrete single-doped with coal gangue coarse aggregate, single-doped with coal gangue fine aggregate, and codoped with coal gangue coarse and fine aggregates. The results show that (1) it is feasible that employing coal gangue to replace natural coarse and fine aggregates in concrete can prepare C30 and C40 concrete; (2) the addition of coal gangue fine aggregate has a positive effect on the impact energy of the initial and final cracks of concrete, while the addition of coal gangue coarse aggregate has a negative effect on it; (3) compared with the static strength, the dynamic strength of concrete is improved no matter whether coal gangue is added to concrete; (4) the incorporation of coal gangue coarse aggregate will make the concrete shear surface smooth; (5) at the given impacting pressure, the concrete with coal gangue coarse aggregate has greater particle breakage and those with coal gangue fine aggregate has less. The research of this study can be a reference for the application of gangue concrete in mine support structures.

MODERN METHODS FOR REDUCING AND OVERCOMING MIN DANGER FOR SHIPS (VESSELS) AND BOATS UKRAINIAN NAVY IN THE BLACK AND AZOV SEAS

This paper considers the problem that exists in the marine space of the Black and Azov Seas and related to the mine danger for warships of Ukraine in certain naval zones of responsibility of the Ukrainian Navy. The authors focused on the fact that the mine danger, which constitutes a real threat to the national security of Ukraine from the sea, not only does not decrease, but also increasesand becomes extremely dangerous.Particular attention was focused on circumstanceswhich might not be known, and were not taken into account when working out decisions on mine defense and mine protectionof the Ukrainian Navy.First of all, this is the existing mine danger in the Black and Azov Seas off the coast of Ukraine, which remained of past wars and post-war active naval activities,as well as from a sea mine threat, which was formed as a result of aggressive actions by the Russian Federation, which threatens Ukraine from the sea. That is, the authors paid special attention to circumstances that might be unknown and were not taken into account earlier when working out decisions on anti-mine defense and anti-mine support for the Ukrainian Navy. This is, first of all, the existing mine danger of the Black and Azov Seas off the coast of Ukraine, which has remained from the past World War II, as well as post-war active naval activities. And secondly, it is preparation and counteraction to possible aggressive manifestations and a mine threat from the side of the country, which constantly threatens Ukraine from the sea. To this end, іn the paper gave specific recommendations on ways to reduce the mine risk for warships of Ukraine and indicated, that in the near future, in Ukrainian Navy it is necessary to activate all existing and well-known components of the mine support system. Ukraine must guaranteedly solve any problems or possible resistance of interested parties in creating the necessary number of mine and mine ships (boats) as part of the Ukrainian Navy.