DEVELOPING METHOD A SLOPE STABILITY ANALYSIS BASED ON ROCK CHARACTERIZATION IN OPEN COAL MINE

• Main Author: Saptono, Singgih
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/55145
• Institution: Institut Teknologi Bandung

Coal production from open pit mining in Indonesia continuously increased by 10 % from 234 tonnes in 2007 to 244 tonnes in 2009. This increase has influenced the changing in the design of mining particularly in the assessment of individual slope of rock mass in open pit coal mining. The location of the research is in the coal mining of PT. Adaro Indonesia, which in general consists of soft rock sediment. Indonesia is located in the tropical region with two seasons. Therefore, the results of the research herein will be suitable to be applied on soft rock in coal mining that is located in tropical region. The study has been done covering laboratory tests, rock mass characterization and shear test of large blocks. The study on shear test of large blocks has been purposed to find out the scale effect of rock shear strength. Meanwhile, the rock samples consist of fine sandstones and coarse sandstones of 25 x 25 cm, 50 x 50 cm, 75 x 75 cm and 100 x 100 cm of sizes, and mud-stone samples of 25 x 25 cm and 50 x 50 cm of sizes. During this study there were steps of designing and constructing equipment for shear test of large blocks. This equipment has been used as a testing equipment and modification of creep shear test equipment for rock samples of 25 x 25 cm of sizes. One of the easiest ways to increase the coal production by changing the mining design is by minimizing the striping ratio, that is by making both individual slope and overall slope as high and as straight as possible. This slope condition will become efficient and effective for mining. However, the slope geometry change mentioned is not necessarily can be applied without finding out what exactly the strength of rock mass to calculate the safety factor. Consequently, it is highly necessary to have a slope stability method, which can determine the slope stability using simple, fast, and accurate criteria. The results of this research is a method to determine slope stability condition based on rock characterization in open pit coal mining. This method is developed using laboratory tests, rock mass characterization and shear test for large blocks. Beside the method of slope stability determination, the study also gained the result findings namely empirical function between frequency of joint towards spacing isv negative exponential function so that the equation of Priest & Hudson (1976) is applied for determining RQD as an alternative in counting RQD from drill core, empirical function for determining compressive strength of rocks in the field between compressive strength of rocks (UCS) and Schmidt Hammer Rebound (R) as an alternative to replace compressive strength with strength index, empirical function in determining GSI towards RMR has corrected equation of Broek & Brown, determination of long term shear strength using visco-elastic behaviour approach has been more appropriately applied with the decrease of strength towards the result of standard shear test to the amount of 57% - 61%. The results of shear test for large blocks show that the scale effect is applied on the cohesion in the sediment rock, yet not for the internal friction angle, the limit of maximum sample size that is still under the scale effect is that of 70 cm. The decrease of cohesion owing to the scale effect is to the amount of 63% - 68% from standard shear test in the laboratory. To obtain slope stability curve is by connecting test result parameter, rock mass characterization and large block shear tests using dimension analysis method. The results are non-dimension product connections of sc, h, g, RMR, c and f, which then are developed, and the result is the curve for determining rock mass cohesion based on RMR and uniaxial compressive strength (UCS), curve for determining friction angle in rock mass based on RMR, and curve for determining individual slope stability based on RMR. All the results mentioned above are the efforts to assess individual slope stability of rock mass in open pit coal mining more practically with accurate results.