بهره برداری از ستون های معدن زغال سنگ پیشرفته با استفاده از روش استخراج دیوار کوتاه؛ یک مثال مورد

The shortwall mining technique is similar to longwall mining but with shorter face lengths, ranging between 40 and 90 m, 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 the 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 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 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 faster exploitation of the developed pillars in the Balrampur mine by shortwall mining.

In India, underground coal production is mostly dependent upon the conventional bord and 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 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) software, 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 field observations of a longwall panel and laboratory tested 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 safe exploitation of the developed pillars by shortwall mining to improve the productivity.

The intact rock properties of different layers of the overlying strata above the Passang seam of Balrampur mine have been calibrated with field observations taken over an experimental panel P-1 for the numerical modelling purposes. These calibrated properties have been utilized for the prediction of expected main fall, suitable orientation of the shortwall face with respect to the advance gallery, and the required support density at the face and in the advance gallery under different combinations of the hard cover. The following conclusions from the above study have been recommended for extraction of the developed pillars of the Balrampur mine with high productivity by the shortwall mining method. (a) Support requirement at the face: The maximum load coming on the powered support applied at the face is 717 ton. Therefore, a support resistance of 103.9 ton/m2 will be adequate to prevent failure of the immediate roof as the face approaches the advance gallery. The overhang of the strong bed number Bed-II must be limited to 15 m from the face by blasting. Further, the canopy length should be chosen such that the face span during normal longwall conditions should not be exceeded by 4.6 m after the cut. (b) Support requirement in the advance gallery: The 4×40 ton traveling supports (made of 4 hydraulic props of 40 ton each with canopy width 2 m and length 3 m) will be sufficient in the advance gallery. A minimum of three such travelling supports are required so as to cover a length of 9 m in the advance gallery at an obliquity of 9°. Maximum load on the supports in the event of failure of the 1 m rib is expected to be 154 ton over a length of 3 m in the advance gallery. Over and above the support recommended in the advance gallery, the immediate roof may be further strengthened by four rows of roof bolts 1.8 m long, at a spacing of 1 m, along the advance gallery and in the level galleries also. The junctions should be supported by W-straps along with bolts. (c) Face obliquity and stability of the triangular rib: It is found that, with an obliquity of 9°, the advance gallery is crossed once in the entire face. Hence, the zone of intense strata movement is also reduced. The safety factor of a 1m thick triangular rib with 9° obliquity is 0.68. It is expected that a rib of safety factor of this level will stand for sufficient time to enable the shortwall face to cross an advance gallery. The face should not be kept idle while crossing this triangular rib. (d) Expected main fall: From the study of 3-D modelling of the developed bord and pillar workings of the Balrampur mine, the expected main fall at different depth of cover with varying hard cover is summarized below. Depth of cover Extraction width Expected main fall 50 m (30 m hard cover+20 m weathered rock) 5 pillars wide between 90 and 100 m 50 m (30 m hard cover+20 m weathered rock) 4 pillars wide between 110 and 120 m 40 m (30 m hard cover+10 m weathered rock 4 pillars wide between 140 and 150 m 40 m (20 m hard cover+20 m weathered rock) 4 pillars wide between 100 and 110 m