Home – Home – Jornals – Advanced Search

Using a gradient-type model, the authors solve a boundary-value problem on stress redistribution in rock mass during mining. The elastoplastic model takes into account local discontinuity. The condition of smoothness of the displacement field is essentially weakened-instead of one smooth field of displacements, two-dimensional kinematics is described using two independent smooth fields. As a consequence, the model receives a structural parameter including the dimension of length and characterizing local bends of unit volumes. The article gives examples of plastic strain calculations in adjacent rock mass with identification of the increased stress concentration zones. It is shown that inclusion of local bends leads, on the hand, to the reduction of plastic shears in adjacent rock mass and, on the other hand, to deeper expansion of high stress concentration zones in rock mass.

This research paper will cover the possible causes which can lead to subsidence above old abandoned board and pillar coal mines at a shallow depth. The research includes the calculation and analysis of the factor of safety for pillars using ANSYS and Monte Carlo Simulations for ascertaining subsidence. An old abandoned coal mine of South Eastern Coalfields Ltd. (SECL, a subsidiary of Coal India Limited) was considered for the study of coal pillar fatigue and eventual crushing of pillars over a long duration of time, simulation analysis of stress and strength of coal pillars over a long period, change in behavior of factor of safety as the dimension of the pillars changes.

The authors assess abrasiveness of sand with continuous acoustic emission recording during LCPC test with crushing of a 500 g sample by a straight wheel in a metal barrel. The informative parameters are the acoustic emission spectra averaged over a number of instances at different times of crushing, and over six frequency bands from 2 to 500 kHz. The obtained coefficients of multiple regression coefficients allow calculating wear of a cutting tool and the LCPC abrasion coefficient LAC for different crushing times by the averaged amplitudes of the AE spectrum components. This method is applicable in tunnel boring, hole drilling and other practices involved in real-time control of ground abrasiveness and wear of cutting tools to be replaced in a timely manner.

According to classification of coal seams with solid inclusions, all mine seams are divided into three groups subject to the size and content of the inclusions in a seam. It is found that fracture efficiency and maximal loads depend on the mineral type of inclusions. Carbonate and pyrite inclusions are fractured in a few cuts, while carbonate-pyrite inclusions are usually broken in a single cut. The loading of a pick is approximately 1.6-1.7 times higher in cutting pyrite inclusions as compared with carbonate inclusions. The authors identify five basic types of the pick-solid inclusion interaction: central and edge cut; touch; tear-out; extraction. The highest loads appear in cutting of solid inclusions and should be taken into account in designs of cutting heads and power drives of mining machines.

The article studies effect of expedient inter-hole delays on seismic safety of blasting in open pit mining. The actual delays in non-electric initiation systems are measured instrumentally, and the results are processed using computer modeling. The domestic and foreign information on deviation of the actual and design delays is reviewed. The computations prove the increase in the factor of seismic safety in blasting with longer inter-hole delays. Additional instrumental measurements of seismic vibrations should be performed to evaluate actual blast patterns at a full and lab scale, with the analysis of quality of rock fragmentation by blasting.

In this study, the change in the strength value of 11 pyroclastic rocks from the Cappadocia region, where pyroclastic rocks are commonly found, using the freeze-thaw (F-T) test was investigated after applying 5, 10, 15, 20 and 30 F-T cycles. The uniaxial compressive strength (UCS) of the samples after applying the F-T cycle was estimated using the point load test (PLT) values. With the developed empirical relationship, it was identified that the PLT values predicted UCS with a high correlation coefficient of 0.8663.

Equipment of open pit placer mining is examined. The process designs of incremental end-to-end gold recovery from placer sands are substantiated. In structurally complex extraction blocks, stripping is carried out first, and then, the limits of rich sand pockets are adjusted during the second-phase denser-grid exploration. Different-grade sands are extracted selectively. Extraction and transport of standard-grade and low-grade sands, which are the bulk of an operating block, is implemented by heavy-duty bulldozes; the standard-grade sands are sent to sluicing, and the low-grade sands are used to make heap leaching piles. High-grade sands, which make a small volume of an operating block, are transported to a multi-stage processing facility for the high-efficiency gold recovery. Tailings of standard-grade and high-grade sand processing, with mainly fine and very fine gold content, go to heap leaching.

In this study, point cloud data were obtained from an underground limestone mine using a laser scanner. A numerical analysis was performed using discontinuous and continuous models, and the stability of two pillars located in large underground openings was analyzed. The safety factor was 1.0 or higher in both analyses, and the displacement was insignificant compared to the pillar size, confirming the pillar stability. Additionally, the safety factor of the discontinuous model was reduced by approximately 30% compared to that of the continuous model, and the displacement was increased by approximately 40%. The change in the safety factor was examined by applying the minimum, average and maximum mechanical properties of the investigated rock mass. The analysis determined that an average change of 50% occurred in the safety factor when the minimum and maximum mechanical properties of the rock mass were compared.

For the operative bucket of a 2nd size-group hydraulic excavator, the impact capacity of percussion mechanisms, required for cutting rocks with the compression strength up to 60-80 MPa, is determined. The structure and parameters of hydropercussion mechanisms are chosen. The proposed inter-connection for the hydropercussion mechanisms and the hydraulic power station contains activation valves for each of the mechanisms, and a pressure reducing valve at the inlet. A simulation model of the system of hydropercussion mechanisms is built, and the performance and characteristics of the model are calculated at different rates of power fluids and pressures of the reducing valve. The authors prove the efficiency of the proposed design and connection of hydropercussion mechanisms in the excavator hydraulics and validate the adjustability of the impact capacity of the mechanisms through setting-up of pressure of the reducing valve.

A bench tester is designed for the examination and investigation of a borehole impulsive source of vibrations, composed of an electromagnetic impact block and hydraulic power units. The bench tester simulates operation of the vibration source in an oil well, at the depths greater than 1000 m, with automated pressure control in the system. The implemented research allowed reaching the failure-free operation time of the vibration source in the well up to 150 h and longer, determining the ranges of the impact frequency and energy adjustment depending on the feed voltage, and recommending the operating frequency of the source to ensure proofness of cement stone of the well casing. The obtained nomograms enable correlating the maximal duty cycle of the borehole impulsive vibration source with the coil current density and the heat transfer coefficient to maintain temperature balance of the hammer at permissible temperature of electromagnets.