Performance behaviour of fully grouted rock bolt as support system

Jun 2017 / by Deepanshu R. Singh and Arvind K. Mishra

Rock bolts are one of the most prominent and economical techniques of rock stabilization used widely in various applications such as mining, tunneling, surface slope stabilization. Various researchers have found that efficacy of rock bolt system depends on the many factors such as annulus space, type of bolt, grouting media, installation mechanism and positioning. Since its inception, many researchers have studied the behaviour of bolts experimentally and analytically. At present in Indian mining industry, the use of fully grouted rock bolts are increasing rapidly owing to the number of accidents in underground mainly due to roof fall. This paper reviews the performance of fully grouted rock bolts under axial loading conditions and presents a case study of an Indian underground metal mine. The review provides an overview of the need for rock bolts to support the roof rock and the bolting system used in Indian mines along with characteristic parameters such as ultimate load, displacement and failure mode under axial load. A study was undertaken to understand the behaviour of fully grouted un-tensioned rebar bolts in an Indian metal mine having competent host rock. The case study describes the performance of fully grouted un-tensioned rock bolt supporting the hangingwall at a depth of 150 m from the surface. The anchorage strength of the bolts were determined in field conditions by conducting pull out test at different durations from the time of installation of the bolt. The generated load-displacement curve shows the debonding nature of the installed bolts under axial loading conditions. The safety factor was calculated for the designing of support system of the mine and the rock load was found using empirical equations using rock mass rating. The safety factor calculation resemble successful application of un-tensioned roof bolt system in supporting an underground metal mine.
Keywords: Rock bolt; tensile load; mining; rock reinforcement; pull-out test

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Experimental studies to evaluate spontaneous heating liabilities of coals: a case study

Jun 2017 / by D. P. Tripathy and S. K. Behera

Spontaneous heating of coal is a major problem worldwide and has been a great concern due to its potential to destroy precious coal resources and cause fire accidents in coal mines. Majority of fires occurring in different coalfields are started by spontaneous combustion of coal. So, extensive research work is being done to characterize the nature and causes of spontaneous heating to prevent its occurrence. In this paper, different properties of coal samples obtained from coal mines under Central Coalfields Limited (CCL) have been evaluated based on: proximate and ultimate analysis, calorific value, FT-IR spectroscopy and DTA. The data obtained was used to compare characteristics of different seams with respect to their tendency towards spontaneous heating susceptibility. From the experimental investigations, it was found that, in general the CCL coals have high ash content, low in moisture (below 2%), and have higher calorific value. The CHNS analysis showed that the sulphur content of the coals is less than 1% in all the cases. Among organic compounds alkane was found to be the most abundant functional group. Based on the transition temperature, it could be inferred that, seam 2 of Sarubera is least susceptible whereas seam 8 of Pindra opencast mine is most susceptible to spontaneous heating.
Keywords: Coal, CCL, spontaneous heating

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Mineralogical characterization of Barsua iron ore slimes and its beneficiation through gravity and 2-stage magnetic separation techniques

Jun 2017 / by S. Patra, A. K. Dash and R. Venugopal

In this study, characterization is done to understand the occurrence, quantity and quality of the ore and its characteristic to establish its physico-chemical properties and to pave way for its beneficiation for economic use. The results indicated the liberation size for beneficiation to be below 150 micron, contains approx. 58% Fe, 2.53% SiO2 and 4.30% Al2O3. Different process such as hydro-cyclone, spiral concentrator and WHIMS were employed in series for the beneficiation of iron. The grade was significantly increased from 57.67% Fe in feed to 63.16% Fe in concentrate. Approx. 30% of SiO2 present in feed is also reduced from 2.53% to 1.77% and approx. 50% of Al2O3 present in feed is removed.
Keywords: Iron ore slime; WHIMS; spiral concentrator; hydro cyclone

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Efficacy of different vegetation methods for stabilization of iron ore fines dump in a surface iron ore mine

Jun 2017 / by Vibhash Ranjan, Phalguni Sen, Dheeraj Kumar and Arjun Sarsawat

The disproportionate increase in the production of iron ore in Odisha has resulted in the accumulation of large quantity of fines ore. Although literature suggests stabilization of dumps using re-vegetation methods, the most effective method of stabilization is still in question. Hence this study was conducted to examine the effectiveness of the three different vegetation methods at fines dump namely, vegetation by coir matting, vegetation by local species and vegetation by grass. This study adopted in-situ jack shear test to find out the most efficient vegetation method for the stabilization of iron ore fine dumps. This study used a customized shear box having a dimension of 0.15m × 0.15 m ×0.15 m, which was specifically designed and fabricated to evaluate the mechanical stability of vegetated fines dump by different vegetation methods. The analysis of field data, graphical presentation and cost analysis has helped us to conclude that the plantation of local species has increased the mechanical stability of fines dump in comparison wth the plantation of grass or coir matting. Further, local species such as Karanj (Ponganna Pinnata), Shisham (Dalbergia Sissoo), Neem (Azadirachta India), Sal (Shorea Robusta), Kendu (Diospyros Melanoxylon), Amla (Phyllanthus Emblical) Jamun (Syzgium Cumini), Banyan (Ficus Benghalensis) and Krishnachura (Delonix Regia) were estimated to be more cost-effective for stabilization of fines dumps, with a possibility of extending its role towards maintaining long term stability, when compared to other methods.
Keywords: Fines dump, re-vegetation, coir matting, local species, grasses, mechanical properties

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Effect of layer thickness of rocks on blast fragmentation – case study in a limestone mine

Jun 2017 / by P. Hembram, C. Sawmliana, R. K. Singh, P. Pal Roy and Rajesh Thakare

The paper discusses the influence of layer thickness of limestone beds on blast fragmentation in different blasting benches of Aditya Limestone Mines of UltraTech Cements Limited. Blast fragmentation analysis was carried out using photographic method to determine the mean fragment sizes. Good correlations were obtained between average layer thicknesses and blast fragment size, power factor (t/kg) and charge factor (kg/m3). Mean fragment sizes less than 100 cm were obtained with the average layer thickness of limestone beds less than 80 cm. The powder factor more than 14 t/kg was achieved with layer thickness less than 200 cm. However, in geologically disturbed limestone strata, blast design patterns and joint parameters had significance in achieving desired fragment size.
Keywords: Lime stone, layer thickness, blast fragment size

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Importance of blast-design in reduction of blast-induced ground vibrations

Jun 2017 / by H. P. Karkar and Rajesh Arora

The dissipated energy generated during blasting creates environmental problems in the form of ground vibration, air overpressure and flyrock. With increasing mining and construction activities in areas close to human settlements, ground vibration has become a critical environmental issue as it can cause human annoyance and structural damage. The magnitude of ground movement was measured in term of peak particle velocity (PPV) with the aid of seismograph. Site constant K, and site geological factor m were determined for both quarries by plotting the graph of the maximum PPV against scaled distance. The data collected for the blasting activities in each of the quarry sites have shown that the peak particle velocities (PPV) recorded varied directly with the charge weight per delay but inversely with scaled distance (SD). A comparative analysis between the results obtained for constant charge per delay and monitoring distance were carried out.
Keywords: Blast-induced vibrations, scaled distance, peak particle velocity, seismograph

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