During blasting,only a small portion of the total available energy of explosive reaction gets consumed in breaking up the rock while most of remaining energy gets dissipated in the form of ground vibration and air overpressure. These side effects of blasting operation not only reduce the powder factor but also prove to be a nuisance for the nearby human settlements and structures, both belonging to and not belonging to the owner of the mine. However, to fulfil the expanding production targets of large opencast mines the deployment of high capacity machines and consequent requirement of deep hole blasting with high amount of explosive consumptions is obvious. In such circumstances, the evaluation of the ground vibration parameters and development of new controlled blasting designs are the needs of the hour. Choice of better initiation system to reduce ground vibration is a major step in this direction. For this, an experimental study was conducted to understand the influence of initiation system on blast induced ground vibrations. In the study, 21 production blasts – 10 using detonating fuse and 11 using electronic detonators, were monitored for ground vibration measurement. The blasts were conducted at the dragline benches of Jayant opencast project. The results obtained from the study revealed that the percentage reduction in ground vibration levels, by using electronic detonators instead of detonating fuse, ranges from 33% to 9% for varying distance from the blast site ranging from 100 m to 1500 m.Read more
The deployment of diesel-powered equipment in underground mines worldwide has increased exponentially over the last few decades. This extensive deployment is associated with serious health and safety hazards due to exposure of miner to toxic gases and diesel particulate matter (DPM) from the exhausts of this equipment. As early as 1988, the National Institute for Occupational Safety and Health (NIOSH) issued a report which stated that diesel exhaust as a whole is a suspected occupational carcinogen. In June, 2012, the International Agency for Cancer Research (IARC) classified diesel exhaust including DPM as a known human carcinogen (Group 1) based on sufficient evidence that this exposure is associated with an increased risk for lung cancer. Also, a positive association, with limited evidence, of an increased risk of bladder cancer was found. The mining industry in India is poised for quantum jump in production of minerals using different level of mechanisation in underground including diesel-powered equipment. Across the globe numerous studies were conducted to identify the health impacts due to diesel exhaust; however, no comprehensive study has been done in Indian mines. It is expected that the extent of the problem will be quite significant in the near future. Further it is important to develop guidelines for controlling the emissions, dilution, monitoring and mitigation of such toxic gases and DPM to help the industry in introducing such technologies safely. In this paper the authors have made an effort to map the exposure of diesel exhaust and DPM in some of the highly mechanised underground metalliferous mines in India and to suggest a draft national standard on the basis of exposure limits set by countries having similar working environment. The authors in this paper have also thrown light into the established control measures for mitigation of the health hazards due to diesel exhaust gases and DPM.
Keywords: Diesel-powered equipment, exhaust gases, diesel particulate matter, health effects, guidelines for controlling emissions
History of Barapukuria coal mine reveals a susceptible condition of subsidence that may obstruct the progressive mining activity. Along with Mohr coulomb failure criterion, authors are scrutinizing the critical stress distribution from the upper strata of minable zone amidst mine. With the steps forward action of mining, the stresses are absurdly acting on further progress which is, in other words, susceptible of subsidence. A number of graphical representations of shear strength in perception of failure load emphasizes on the vulnerable situation of subsidence that follow the similar manner of Mohr coulomb failure envelope. On account of Mohr Coulomb failure criterion, the critical pressure of above strata has estimated about 4.5 MPa whereas the actual overburden pressure is 4.67 MPa that exceed the critical value; therefore, resulting an alarming condition of destruction. The volume of the backfilling materials is equal to the volume of the void that occurs due to the extraction of coal in the central part within an area of 1.2 km2. The estimated volume of backfilling materials is about 3.6×106 m3.
Keywords: Critical stress distribution, Mohr coulomb failure criterion, shear strength, backfilling
On the basis of previous studies, the factors affecting the behaviours of SiC whisker dispersion are analyzed. The main contents of the analysis are:The impact on silicon carbide whisker in aqueous medium relative sedimentation height and surface potential value are made by the changes of the pH value. The impact on the silicon carbide whiskers and silicon carbide particles of two different crystal surface zeta potential made by the change of pH value, effects that SHP and CMC, two kinds of dispersants have on the relative settling height of silicon carbide whiskers and the infrared spectroscopy analysis before and after using the two dispersants. It is concluded that, without dispersing agent, the stable dispersion system of silicon carbide whisker is difficult to obtain by adjusting the pH value, and the morphological characteristics of the silicon carbide crystal have obvious influence on the dynamic potential on the surface. The dispersion mechanism of the two dispersants is different, in which the dispersion mechanism of SHP is to improve the repulsion of the surface of the material, and the dispersion mechanism of CMC is to increase the hydrophilicity of the surface of the material and increase the absolute value of the potential of the whisker surface. By means of adjusting the pH value and adding dispersants, we can get a more stable silicon carbide whisker dispersion system.
Keywords: SiC whisker; pH value; potential value; relative settlement height; infrared spectrum; dispersion effect
Blasting is a dynamic process in which rock is broken into smaller fragments, so that, it can be loaded and hauled with least effort and hence investment. The performance of the mine to mill system thus is mainly dependent on the fragmentation that in turn should be of optimum size. Understanding the fracture mechanics of a particular rock is thus quite imperative. Understanding the breakage of rockmass is very important because it ultimately helps in evaluating the performance of equipment vis-a-vis optimum fragment size that finally dictates the mine economics. The outcome of a blast is dependent on several variables belonging to rockmass and blast design. While blast design variables are controllable, the rock variables are of uncontrolled nature and hence difficult to simulate. One of the rock properties is its stiffness that has an impact on breakage of rock and is the subject of this paper. In order to determine the behaviour and fracturing during dynamic loading simple models representing blast benches were constructed using Particle Flow Code2D. Few simulations of throw, stemming movement and heave were made while varying the stiffness of material and keeping all other parameters constant. The paper thus reports the results obtained from such simulations.
Keywords: Particle flow code, blasting, fracturing, homogeneous material, material properties
The electrochemical behaviour of TEM based on SiC particle reinforced magnesium matrix composites has been investigated. The research result indicates that the corrosion rate of SiCp/AZ91 MMCs was significantly higher than AZ91 magnesium alloy, and increases with the increase of the volume fraction of SiC particles; the corrosion morphology mainly along the micro-galvanic corrosion occurs around SiC particles, with the increasing of SiC volume fraction, the micro-galvanic corrosion of SiC particles and AZ91 interface of SiC and AZ91 particles are not serious; the micro-galvanic matrix directly, but the addition of SiC particles changed the micro-structure of SiCp/AZ91 MMCs can increase the corrosion rate. The main reasons are: with the addition of SiC particles of β phase grain refinement, the effect of β on cathodic hydrogen phase enhancement, thus accelerating the micro-galvanic corrosion of β phase and α phase; furthermore, the addition of SiC particles to make a large number of β phase at the interface of SiC particles and AZ91 matrix at first recrystallization, causing to accelerate the micro-galvanic corrosion of β phase interface and α phase and SiCp/AZ91 MMCs, indirectly lead to accelerated corrosion.
Keywords: Magnesium alloy; magnesium matrix composite; corrosion behaviour; SiC particles; α phase and β phase
In order to improve the mechanical performance of ceramic, using the application of short carbon fiber as reinforcement, the dense homogeneous zirconia coating was prepared by sol-gel method on the surface of short carbon fiber. Then RBSC composite material was obtained, through the grouting and reactive sintering two steps. At the same time, the article studied the microstructure and mechanical properties of RBSC to reveal its morphological changes, when fiber content was between 10% and 40%. And the article studied the mechanism of toughing of fiber, according to the characteristics of the fracture and the conductive path of the crack. The carbon silicon reaction is the basis of sintering, so the article studied the effect of carbon black content on the properties of silicon carbide. The results showed that the critical value of short fiber content is 30 vol %, and SC12Cf30 is the maximum value at the same time. The increasing contents of carbon black will improve secondary β-SiC volumes. The carbon-silicon reaction releases heat, which improves the β-SiC crystal refinement and leads to the concentration of free silicon decreases, thus increasing the bending strength of the material.
Keywords: Short carbon fiber; sol-gel process; fiber content; bending strength