Longwall Top Coal Caving Design for Thick Coal Seam in Very Poor Strength 1 Surrounding Strata 2

Alpu lignite field is an important coal deposit with nearly 2 billion tons of coal resources located 11 in the middle of Turkey. The mine deposit consists of three main seams. The thickness of two 12 of them vary from 4 m to 30 m. The surrounding rock mass is very poor in terms of strength. 13 The high clay content and weak rock mass make mechanized mining difficult. In this research, 14 applicability of the longwall top coal caving method was investigated. The very weak strength 15 behavior of the coal and the surrounding strata increases the importance of research in the mine 16 site in terms of ground control. The aim is to design the mechanized longwall mine based on 17 ground control principles. First of all, classification of the roof, coal, inter-burden, and floor 18 strata were classified based on geotechnical aspects. Then, cavability index, shield, and floor 19 bearing capacity were investigated. Different methods were applied to understand the 20 limitations of a mechanized system that is very critical due to the very low strength strata. 21 According to the main results, roof strata was classified as immediately caving while mining 22 height was calculated as 5 m to 6 m. Finally, the relations among geotechnical characterizations 23 of roof and floor strata, cutting and caving heights, and required shield capacity were presented 24 based on analytical and numerical applications. The proposed approach can be used as a ground 25 control method for the applicability as well as the limitations of mechanized longwall mining 26 design in weak strata conditions.

very low strength definitions. The study aims to investigate the applicability of LTCC as a 23 mechanized underground production method. Caving behavior was simulated for required 24 shield capacity investigations. In addition, floor bearing capacity was researched for the 25 hydraulic shields and AFC designs. Analytical and numerical methods were also performed in 26 this study for the design of LTCC in thick coal seam that is seam-A. Furthermore, application 27 of conventional mechanized longwall mining was investigated for seam-C as an auxiliary 28 purpose of the study. longest distance from north to south is 5 km and from east to west is 6 km. The location map 1 and an aerial image of the license area can be seen in Fig. 2. 2 Turkey coal deposits mostly took shape during the carboniferous and tertiary periods. Alpu 3 lignite mine site is located in Sakarya terrane and Anatolide tauride block, which is separated 4 by the Intra-pontide suture zone passing through the Bozuyuk-Eskisehir line (Toprak et al.   (Asutay et al. 1996). A geological map and a cross-section are given in Fig.3 and Fig. 4, 16 respectively. 5/28 method for seam-A while conventional mechanized longwall mining method is selected for 1 seam-C.  Table 1. Intact rock and rock mass properties 11 were then quantified from the site and the laboratory studies.  The average values of the test results are presented in Table 2. Physical properties and slake 12 durability index values can be seen in Table 3.
The results are quite interesting due to its very low values. All materials apart from the Brief information can be found in Table 4     average value of rating and calculated RMR are given for each rock mass in Table 6.    Similarly, K2 can be assumed as 0.7 for sandstone and 0.6 for mudstone, claystone, or siltstone.

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Finally, K3 is 0.6 for sandstone, 0.4 for claystone and mudstone with 50% relative humidity.  where DSR is discontinuity spacing rating. applying detached roof block model for the study area, which is outlined in Fig. 5. The 26 parameters used in the method are presented in Table 9, separately. The parameters used in the 27 design studies are summarized in Table 10 that are determined from coal and surrounding strata (2) 13/28 The very poor strength of the roof and floor causes to search for different production 1 alternatives. Three alternatives were performed in seam-A which are named as LTCC and 2 sublevel production, LTCC and sublevel production with pillar, and sublevel conventional 3 mechanized longwall mining. The alternatives are illustrated in Fig. 6. from the design studies, which are presented in Table 11.

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In the second alternative, the upper part of seam-A that contains a lower calorific value (less 12 than 1000 kcal/kg) according to the exploration study leaves as a pillar. This helps to decrease 13 the amount of weight in the immediate roof that also decreases the load on the hydraulic shield.
14 The thickness of the pillar was assumed as 5 m. The same calculation procedure was also 15 applied for the second alternative and the results are presented in Table 12. 16 Finally, the third alternative was applied for the design of conventional mechanized longwall 17 mining application in case of the unavailability of the LTCC method. The production will also 18 be applied in sublevels. In other words, slices and the production are only performed in advance 19 instead of the top coal. Different mining heights were studied again and the results are presented 20 in Table 13. According to the bearing capacity of the floor for both coal and claystone, the 21 available height can be changed from 2 m to 4 m as per the analyses.

Hydraulic Shield Support and Floor Bearing Capacity for Seam-C
10 however, the value was sometimes very low or the material was classified as the soil in some 23 locations. Thus, geotechnical conditions were assumed as the weakest link for the site and once 24 the production panel was projected and a geotechnical study must be conducted to understand 25 the distribution of floor bearing capacity for the applicability of mechanized mining. This 26 application should be applied for the entire production schedule at Alpu lignite field. Therefore, 27 the amount of reserve that is defined as the producible amount of mine resource is totally related 28 to the ground stability of coal seams for the project site.  The boundary conditions were fixed at zero. One of the finite element model was presented in analyses, are presented in Fig. 8 for normal stress distribution, Fig. 9 for horizontal stress 10 distribution, Fig. 10 for strength factor, and Fig. 11 for yielded elements.

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The increasing cutting height results in the increasing amount of stresses for both normal and  According to the feasibility studies, a LTCC mechanized system will be implemented for seam-9 A, and a conventional mechanized longwall mining system is designed for seam-C. Due to the 10 threshold value of thickness, seam-B is not projected for the production. Geotechnical The low strength of the roof may also cause instability in the roof and face in longwall.

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The primary outcomes of the study present that Alpu lignite field will be the first example that