مدل رگرسیون لجستیک برای پیش بینی خطرات سقوط سقف در کار برد و ستون در معادن زغال سنگ: یک روش
|کد مقاله||سال انتشار||مقاله انگلیسی||ترجمه فارسی||تعداد کلمات|
|24763||2009||9 صفحه PDF||سفارش دهید||5248 کلمه|
Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Safety Science, Volume 47, Issue 1, January 2009, Pages 88–96
The roof fall hazards are the major problems in underground coal mines, which are generally unpredictable due to the associated uncertainties arising out of the complexity of geological conditions and variability in mining parameters. During the six year period, 1996–2001, 253 Indian coal miners lost their lives and 401 are seriously injured in 490 different roof fall accidents. In India, 32.7% of the total fatal injuries in coal sectors are due to roof fall in bord and pillar method of workings. This paper attempts to predict the severities of roof fall accidents based on some major contributing parameters using the binary logistic regression model. In total, 128 roof fall accidents for the last few years from five underground coal mines in India having bord and pillar method of working are analyzed for this study. The results revealed that wider gallery width is more prone to major and serious accidents than narrower gallery width. Thin seams are more amenable to major accidents in comparison to thick seams. Unsupported or partially supported roofs have higher risk for contributing major as well as serious accidents. Deep workings are more prone to major accidents as compared to shallow depth workings.
Roof falls continue to be one of the greatest single hazards faced by underground coal miners. The hazardous nature of roof falls in underground coal mine operations can be illustrated from the national statistics of mine accidents. During the six year period, 1996–2001, in India, 253 coal miners lost their lives and 401 are seriously injured in 490 different roof fall accidents. 32.7% of the total fatal injuries in Indian coal sectors are due to roof fall in bord and pillar method of working; whereas only 1% of the total fatal injuries due to roof fall are occurring in longwall method of working (DGMS, 1996–2001). The roof fall accident rates are less in longwall faces, since they are very few in number, mostly mechanized covering the working faces with powered roof supports and galleries with the combination of roof bolting, props and bars, and also areas of exposure due to drivage of galleries are much smaller than the bord and pillar method of working (Das, 1984). In underground coal mining, bord and pillar is the method of working, mostly preferable for flat tabular deposits in thin seams, where bords or galleries are driven in the solid coal to form pillars in the development workings. ‘Pillars’ of coal are left behind to support the roof and prevent collapse. Additional support is provided through the use of roof bolts and props. In some cases, the pillars are removed partly or fully in a later operation known as bord and pillar depillaring. The complexity of geological deposit and variability of mining parameters leads to the occurrences of unwanted roof falls. There are various studies on finding relationship between the roof falls and geological conditions, stress state and mine layout (Molinda et al., 2000, Das, 2000 and Phillipson, 2003). Phillipson (2003) emphasized on geological mapping for ultimate benefit of understanding the geology and projecting the zones of adverse ground conditions for the prevention of fatality. The identification of many slickenside features as faults and shear zones, which are true structural geologic features, increases the importance of basic structural geologic mapping in coal mines. Interpreting slickenside formation in terms of structural geology can allow areas of poor ground conditions to be projected ahead of mining, so that additional support measures can be planned in advance. Das (2000) studied the behaviour of coal measure roof rocks during mining, considering the geology and physico-mechanical rock properties. Molinda et al. (2000) performed simple regression analysis with some significant geotechnical variables like overburden, bolt strength, bolt capacity, grout length, density, entry width, coal mine roof rating (CMRR) and intersection span for predicting the roof fall rate. The results showed that there is relationship existing between intersection span and entry width; CMRR and overburden; CMRR and bolt length. For stronger roofs (high CMRR), shorter bolts are required, and there is a positive correlation between CMRR and depth of cover. Depth of cover is one of the major factors for the ground falls, as it is an indirect representation of the horizontal stress (Dolinar et al., 2001 and Molinda et al., 2000) affecting the roof geology and the pillar strength. In most of the countries, mine workings having depths less than, or equal to 120 m are regarded as shallow depth category and more than 120 m, as deep mines (Dolinar et al., 2001). In their study, for the guidelines of roof bolt design, though they found statistically, the effect of depth of cover was relatively weak with all other geotechnical variables remaining the same, stated deeper mines are more likely to have high roof fall rates. Besides depth of cover, another important factor is the width of gallery. The relationship of gallery width with factor of safety of pillars has been well established and the immediate roof rocks may be classified as weak, or strong (Das, 1994). The management of roof fall risks in underground coal mines is explained by Duzgun and Einstein (2004) with the probability of roof fall, and cost of consequences by relative cost criterion. They provided two alternative methods of “do nothing” and go for “support improvement” by the cost-benefit analysis in their decision framework. A comparative study is conducted for a group of five underground coal mines in India for the reliability of mine for roof fall accidents and estimation of roof fall risks by Monte Carlo method (Palei and Das, 2005). Their results revealed that the probability of roof fall of a mine did not identify the overall risk, because the other component of risk, i.e. the costs of consequences of such roof fall accidents also play an important role. Accident ratio (i.e. reportable injury:serious injury:fatality) studies indicated that there are many more minor injuries experienced than serious injuries and that for the same serious injury there have been numerous property-damage accidents and there are a large number of near-miss cases too. Bhattacherjee (2000) identified that for a group of six Indian coal mines, the four year ratio of reportable injury to serious injury to fatality was 50:5:1. A special attention is paid in this paper on the assessment of the risk of roof fall accidents of different severity in the coal mines having bord and pillar method of workings. The major contributing parameters may be categorized into different groups, which are responsible for unwanted outcomes. The contributing parameters has been grouped into two classes namely (i) geo-mining variables, such as gallery width, mining height, depth of cover, seam thickness, roof support status, and immediate roof and (ii) location variables like roof fall location and the individual mine. A binary logistic regression model is used for this study.
نتیجه گیری انگلیسی
This paper focused on evaluation of severities of roof fall accidents in bord and pillar method of working through the application of logistic regression model. Again, logistic regression model deals with probability function and treats each individual as a separate observation to estimate the probabilities. On the basis of the model results, the unsupported, or partially supported roofs are more prone to major accidents than the supported roofs, but the earlier study by Biswas and Zipf (2003) only noted more ground fall incidents in supported areas (67.6%) than the unsupported areas (32.4%) in their taxonomic analysis. The variable like workplace locations have not had statistical significance in this study, whereas Maiti (2003) in his study of occupational risk of underground coal miners found outbye locations are more accident-prone workplaces than the faces. The specific conclusions for the case study mines based on the available roof fall dataset are summarized below: (i) Unsupported or partially supported roofs are more prone to major accident than the supported roofs. (ii) Deep workings (>120 m) are more prone to major accidents in comparison to shallow depth workings (⩽120 m). (iii) Widened galleries (⩾4.2 m) are more prone to major accidents than the narrower width galleries (<4.2 m). (iv) Less thick seams (⩽4.8 m) are more amenable to major accident in comparison to thick seams (>4.8 m). (v) A solemn attention should be paid on the support design based on the depth of super incumbent strata, restricting the gallery width to reduce the risks of roof fall.