Risk Assessment of Open Pit Slope Design at PT Adaro Indonesia (original) (raw)
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The stability of mining slopes, especially on tin minerals, has different criteria than other minerals. The safety factor that becomes the reference value of the stable slope of the mine can also reflect the movement of the land (Lubis, 2012 in Wijayanti, 2015). In processing these FK values often do not take into account that all parameters have equal oppurtunity to represent those parameters (Azizi, 2012). The probability method is a way of anlyzing the risk of mining slopes by including several parameters including wet density, dry density, cohesi and friction angle. The research aims to get FK and PK values that are stable and efficient to be mined because the smaller than the slope is opened, the smaller the tin mineral recovery and the higher the stability of the slope and vice versa. To get the value of FK and PK need to do slope analysis with limit equilibrium method and probability method then modeled with Slide V.6.0 software and calculation with Excel program. Data processing is from 4 drill points found that GT_01 with value FK > 1,3 indicating that the slope safe and movement of soil can occur and get value PK 0,5-0,6 %. For GT_02, GT_03 and GT_04 obtained unsafe slope results so optimization is necessary.
Probability Methods for Stability Design of Open Pit Rock Slopes: An Overview
Geosciences, 2021
The rock slope stability analysis can be performed using deterministic and probabilistic approaches. The deterministic analysis based on the safety concept factor uses fixed representative values for each input parameter involved without considering the variability and uncertainty of the rock mass properties. Probabilistic analysis with the calculation of probability of failure instead of the factor of safety against failure is emerging in practice. Such analyses offer a more rational approach to quantify risk by incorporating uncertainty in the input variables and evaluating the probability of the failure of a system. In rock slope engineering, uncertainty and variability involve a large scatter of geo-structural data and varied geomechanical test results. There has been extensive reliability analysis of rock slope stability in the literature, and different methods of reliability are being employed for assessment of the probability of failure and the reliability of a slope. Probabi...
Considerations on the Probability of Failure of Mine Slopes
Soils & Rocks, 2012
Probabilistic and deterministic stability analyses of the progress of a large mine pit excavation in Brazil are presented herein. A simple method of reliability analysis for quantifying the probability of failure of slopes has been considered and its advantages and limitations are briefly discussed. The variance of the factor of safety is computed for several stages of the mine excavation. It is shown that, depending on the slope height, either the friction angle or the effective cohesion may be the most important variable controlling stability. In the case of mine pit excavations ranging from 50 to 400 m in height, pore pressures are of lesser relative importance. Consequently, increasing the capacity of the horizontal drainage system may be of limited efficiency in stabilizing potentially unsafe mine slopes. In addition, variables with no significant effect on the stability, such as the apparent specific gravity of the slope material, may be simply considered as deterministic parameters.
IOP Conference Series: Earth and Environmental Science
Batu Hijau is a gold mine which is now run and managed by PT Amman Mineral Nusa Tenggara (PT AMNT) with open mining method. The located in Sekongkang District, West Sumbawa Regency-West Nusa Tenggara Province. The geological structure aspects are interesting as objects in this study, due to the condition is very tight and become to trigger for the slope failure. Slope stability is one of the important terms for supporting in open pit mining activities. One of the slope failure indication is the failure caused by the structure. Geological structure analysis performed with kinematic analysis which takes into account the probability of failure and type of failure. The probability of Failure can count by structure orientation, the orientation of the mine slope design, and friction angle with using dips 6 software. The percentage of slide obtained from the ratio between the critical point from the critical zone with the total critical point in stereographic projection. The count applied in all geotechnics domain with inputting of parameter structure orientation, the orientation of the mine slope design, and friction angle. The result shows between 0% to 2.63% of planar failure. The percentages show probability of failure but still in the safe category with 10% safety limit. Slope safety factor counts manually based on the mathematical formula applied to all domains in Batu Hijau Open Pit Mining. The result shows the value between 1.04 to 1.905 on planar failure. This value shows the condition of slope in the research site is stable.
Geotechnical and …, 2011
Nowadays, there are many new methods for slope stability analysis; including probabilistic methods assessing geotechnical uncertainties to develop safety factors. In this paper, a reliability index analysis for the Sungun copper mine slope stability is evaluated based on three methods of uncertainties consisting Taylor series method, Rosenblueth point estimate method and Monte-Carlo simulation method. Sungun copper mine will be one of the Iran’s biggest mines with final pit’s height of 700 meters. For this study two of its main slopes were assessed, one dipping to the NE (030) and the other to the SE (140). Probability density function of cohesion and angle of friction for the slopes were developed using limit equilibrium methods. These shear strengths were then used to determine the probability density function of safety factor and reliability index using the probabilistic methods. Results of the probabilistic analysis indicate that with ascending values of the uncertainties the reliability index decreases. Furthermore, it was determined that with the Monte Carlo simulation the seed number used has little effect on the reliability index of the safety factor especially with seed numbers in excess of 1200. Variations in the overall reliability index of safety factor were observed between the two slopes and this difference is explained by the differences in complexities of the geology within the cross-section.
A risk consequence approach to open pit slope design
The Journal of the Southern African Institute of Mining and Metallurgy, 2006
Open pit slope design has conventionally been effected as a bottom up function utilizing available geotechnical information. This results in a decision criterion based on probability of failure and factor of Safety with a risk assessment being carried out on the proposed design slopes. The design approach recommended reverses the process using fault event tree decision methodology. The consequences of this approach are that acceptable risk criteria have to be determined by mine owners. Slopes are then designed by the technical staff to achieve these corporate goals. Benefits that arise from the process are that the owners take a proactive decision on the risk-benefit relationship allowing the technical staff to optimize the geotechnical exploration programme and design.
Risk Evaluation of Slope Failure at the Chuquicamata Mine
2007
The possibility of increasing the pit slope angles of the Chuquicamata Mine as the pit approaches its planned closure is being considered. Compared to the conventional mine design, the slope steepening is understood to raise the net present value (NPV) of the mine, but also, attracts an increase in possible adverse outcomes related to the increase in the likelihood of slope failures. A quantitative risk evaluation was undertaken to provide information to assist the mine management in their decision by: defining risks in terms of safety and economics, quantifying risk level for different slope configurations and comparing results against industry norms. The approach included three main tasks: (1) evaluation of the total probability of failure (POF) representative of the stability conditions of slopes. (2) Evaluation of the consequences of slope failure on safety of personnel. (3) Evaluation of the consequences of slope failure in terms of economic losses associated with impact on equ...
Quantitative hazard assessment system (Has-Q) for open pit mine slopes
International Journal of Mining Science and Technology, 2018
Rock slope hazard assessment is an important part of risk analysis for open pit mines. The main parameters that can lead to rock slope failures are the parameters traditionally used in geomechanical classifications, the slope geometrical parameters and external factors like rainfall and blasting. This paper presents a methodology for a hazard assessment system for open pit mine slopes based on 88 cases collated around the world using principal components analysis, discriminant analysis and confidence ellipses. The historical cases used in this study included copper, gold, iron, diamond, lead and zinc, platinum and claystone mines. The variables used in the assessment methodology are uniaxial compressive strength of intact rock; spacing, persistence, opening, roughness, infilling and orientation of the main discontinuity set; weathering of the rock mass; groundwater; blasting method; and height and inclination of the pit. While principal component analysis was used to quantify the data, the discriminant analysis was used to establish a rule to classify new slopes about its stability condition. To provide a practical hazard assessment system, confidence ellipses were used to propose a hazard graph and generate the HAS-Q. The discriminant rule developed in this research has a high discrimination capacity with an error rate of 11.36%.
AN APPLICATION OF POINT ESTIMATION METHODS TO ASSESS OPEN PIT SLOPE STABILITY
XIV Congreso International de Energia Recursos Minerales, 2018
Open pit slope stability is typically assessed using deterministic methods. A single value for the factor of safety is calculated using a single set of input parameters and is assumed to represent the overall stability of the slope. A limitation of the deterministic approach is that it does not account for the natural variability of the input parameters or the uncertainty caused by sampling. The probability associated with the factor of safety is often not estimated and, although the input parameters are typically average values of existing data, this probability may be small because the likelihood of the average values occurring simultaneously is usually low. Reliability based methods overcome some of the limitations of deterministic methods by incorporating the natural variability of key input parameters and allowing the evaluation of cumulative distribution functions that can be used to quantitatively describe the likelihood of achieving or not achieving a certain factor of safety. In the latter case, the probability of failure can be assessed and represents the likelihood of having, for example, a rock discontinuity with persistence greater than a certain length, dip steeper than a certain angle, or strength lower than certain values. This paper presents a feasibility level geotechnical study undertaken using point estimation methods in combination with discrete fracture network modelling and limit equilibrium methods to evaluate the probability of failure of a proposed open pit slope. This paper describes the process followed to develop the probability density and cumulative distribution functions for the factor of safety by taking into account the natural variability in orientation, continuity, and strength of rock discontinuities. The statistical distribution of the factor of safety is presented and is used to assess the pit slope stability in terms of probability of failure and acceptable risk tolerance.