1、PDF外文：http:/ 6660 字 出处： International journal of rock mechanics and mining sciences, 2005, 42(1): 127-136 英文原文 Exploitation of developed coal mine pillars by shortwall mining a case example A. Kushwaha, G. Banerjee Central Mining Research Institute, Barwa Road, Dhanbad 826001
2、, Jharkhand, India Abstract: The shortwall mining technique is similar to longwall mining but with shorter face lengths, ranging between 40 and 90m, with the aim of controlling the caving nature of the overlying upper strata, the load on support and the overall operation of the supports applied at t
3、he face. Field observations and three-dimensional numerical modelling studies have been conducted for the longwall panel extraction of the Passang seam at Balrampur Mine of SECL to understand the caving behavior of the overlying upper strata. A large area of the Passang seam adjacent to the longwall
4、 panels has already been developed via bord and pillar workings. In this paper, numerical modelling studies have been conducted to assess the cavability of the overlying strata of the Passang seam in the mine over developed bord and pillar workings along with the support requirement at the face and
5、in the advance gallery. The caving nature of the overlying rocks characterized by the main fall is predicted for varying face lengths, strata condition and depths of cover. The support resistance required at the face, the load in the advance gallery and its optimal obliquity were estimated for faste
6、r exploitation of the developed pillars in the Balrampur mine by shortwall mining. Keywords: Exploitation； Shortwall mining； Geo-mining； Obliquity； Block contours； Main fall； Advance gallery 1. Introduction In India, underground coal production is mostly dependent upon the conventional bord an
7、d pillar (room and pillar) method of mining, although the overall output per man shift (OMS) through this method is generally not more than 1 ton in any of the mines 1. Large areas in all the subsidiaries of Coal India Limited and even in Singarani Coal Companies Limited (India) have been developed
8、via bord and pillar workings. There is a need to search for a new method of mining for the faster exploitation of these developed pillars to improve productivity. In this paper, the authors have conducted different numerical modelling studies using Fast Lagrangian Analysis of Continua (FLAC) softwar
9、e, to assess the cavability of the overlying strata of the Passang seam in Balrampur Mine of SECL (India) over developed bord and pillar workings along with support requirements at the face and in the advance gallery. This study is based on eld observations of a longwall panel and laboratory tested
10、data of the overlying roof rocks as the input parameter for the modelling. The caving nature of the overlying rocks characterized by the main fall span is predicted for varying face length, strata condition and depth of cover. Further, optimal obliquity of the face was also estimated for faster and
11、safe exploitation of the developed pillars by shortwall mining to improve the productivity. 2. Shortwall mining Bord and pillar mining will not be a suitable option for developed pillars at higher depth cover in terms of productivity, safety and percentage of recovery. The technology of shortwall mi
12、ning overcomes most of the limitations experienced in operating longwall mining. In the Indian context, a face length of about 90m is economically optimum with a moderately priced shearer and earning per man shift (EMS) as observed in the Indian longwall mining faces 2. Shortwall mining of the devel
13、oped bord and pillar workings would be a good option to overcome the limitations of the conventional bord and pillar method of mining. 3. Status of the Passang seam of Balrampur mine The geo-mining parameters of the proposed area of the Balrampur mine for shortwall mining panel are given below. Thic
14、kness of the seam 2.4m Proposed height of extraction 2.4m Depth of proposed panel 37-50m Existing overlying/underlying workout areas Nil Existing mining pattern Developed on bord and pillar workings Pillar size 20m20m(center to center) Gallery width 4m Various boreholes have been drilled over
15、the longwall panels P-1 and P-2 of Passang seam of Balrampur mine of the same area with results as given in Table 1. The average hard cover in panels P-1 and P-2 were 29 and 39m, respectively, and the depths of the seam were 50 and 53.1m, respectively. Based on the eld observations of the caving nat
16、ure of the overlying strata of the longwall panel P-1, the overlying strata have been divided into six major beds overlying the coal seam. Based on engineering judgement and giving a higher weight to the borehole lithology in panel P-1, estimated RQD and the intact average compressive and tensile st
17、rengths of different bed rocks tested in the laboratory 3 are given in Table 2. From the borehole details, it is evident that Bed-I and Bed-III are weak beds, with RQD of 40% and 43%, respectively. Bed-II and Bed-IV are relatively strong with RQD of 78% and 75%, respectively. It is expected th
18、at these two strong beds will pose difculty for caving. Bed-V and Bed-VI consist of fractured/weathered rock and alluvial soil. Table 1 The borehole details over longwall panels P-1 and P-2 at theBalrampur mine Borehole no. Depth of seam(m) Seam thickness(m) Hard cover(m) BIX-145 (behind panel P-1)
19、47.50 2.32 26.30 BIX-146(middle of panel P-1) 49.30 2.28 24.30 BIX-144 (at the end of panel P-1) 48.90 2.50 38.55 BHP-2.1 (over panel P-2) 51.25 2.90 33.00 BHP-2.3 (behind panel P-2) 52.49 39.39 BHP-2.3 (over panel P-2) 53.6 2.60 41.00 BHP-2.4 (over panel P-2) 54.70 1.50 42.00 4. Field experiences o
20、f alreadyextracted longwall panel Longwall panel P-1 with a face length of 156m, situated at an average depth cover of 50m at the Balrampur mine was extracted with the help of the rst Chinese powered support in 1998. In this panel, local falls had started taking place at regular intervals after a fa
21、ce advance of 25m, involving the immediate roof fall of around 5m height, lling approximately 60% of the void in the goaf. On 26th May, 1998, when the face advance was 67m, a fall of considerable extent was observed. It appeared to be the main fall but no subsidence was recorded at the surface. Late
22、r, the main fall took place on 28th May 1998 at a distance of 7980m from the barrier. This loading caused extensive damage to the powered supports installed at the face and subsidence was observed on the surface. This was recorded as the rst main fall. Table 2 Representative lithology above the Pass
23、ang seam, plus their intact properties Bed No. Run up wards(m) Rock types Thickness (m) RQD(%) Compressive strength (MPa) Tensile strength(MPa) Bed- 0.5-5.51 Coal Medium grained sandstone, laminated with shale 2.4 5.51 - 40 23.8 10.96 2.5 1.5 Bed- 5.51-12.17 Coarse grained to medium grai
24、ned sandstone 6.66 78 17.1 1.4 Bed- 12.17-16.02 Very coarse grained sand stone 3.85 43 13.92 1.4 Bed- 16.02-30.00 Medium grained sand stone 13.98 75 14.5 2.2 Bed- 30.00-41.00 Weathered rock 11.00 - - - Bed- 41.00-50.00 Sandy soil 9.00 - - - 5. Cavability analyses of the overl
25、ying strata Numerical modelling for shortwall mining of devel-oped bord and pillar workings was conducted using FLAC 3D software with the tested and calibrated rock mass properties. This model study was undertaken with a face length equivalent to four pillars (84m) and ve pillars (104m) wide, along
26、with variation in depth and hard cover, to understand the cavability of the roof strata. The main fall position during the shortwall mining with varying face length and depth of cover was predicted. The following geometry was modelled: Average thickness of seam 2.4m Depth of cover 50 and 40m Hard co
27、ver/Alluvial soil for 50m depth cover 30m/20m Hard cover/Alluvial soil for 40m depth cover 20m/20m and 30m/10m Pillar size (Center-to-Center) 20m20m Width of gallery 4m Face length 84m/104m In the absence of the in situ measurements of stress values, theoretical values were calculated using the following equation: )1000()1(1 HEGvh (1) where v and h are the vertical and horizontal stresses (Mpa), E, Youngs modulus of
