Risk Evaluation of Slope Failure at the Chuquicamata Mine (original) (raw)
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Geotechnical risk analysis for the closure alternatives of the Chuquicamata open pit
Proceedings of the First International Conference on Mining Geomechanical Risk, 2019
The development of the geotechnical risk model for the Chuquicamata mine started in 2005 and included the safety and economic impacts of slope failures at different scales (Tapia et al. 2007; Steffen et al. 2008). The model has been updated recently to include a quantitative evaluation of large economic impacts derived from inter-ramp and overall slope failures using a probabilistic approach (Contreras 2015). This paper describes how the later component of the model was used as a tool for the evaluation of four closure alternatives for the open pit. The methodology included three main tasks: 1. Evaluation of the Probability of Failure (PF) representative of the stability conditions of pit slopes. 2. Evaluation of the consequences of slope failure associated with economic losses derived from impacts on production and costs. 3. Generation of risk maps to compare several closure alternatives. The results of these analyses provided information on magnitude of impacts and their likelihood for the four closure alternatives evaluated. The evaluation of these results facilitated the selection of the appropriate closure alternative considering the mine reference criteria for economic risk.
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.
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.
Risk Assessment of Open Pit Slope Design at PT Adaro Indonesia
2014
Risk assessment of open pit slope stability is an important aspect to be considered in a decision making of slope design. The risk of slope failure that occurred on the slopes of the mine affect two factors namely the failure probability (FP), and consequences (C) of slope failure. FP is obtained from the collection of the value of Safety Factor (SF) < 1 compared to the total value of SF, while the consequences is estimated from the sectional area multiplied by the width of slope failure. Physical and mechanical properties of sandstone was collected from PT Adaro Indonesia, and tested by “Kolmogorov-Smirnov (K-S)” fitting method to obtain an assumed theoretical distribution that be sued with the character of the original distribution data. “Monte Carlo (MC)” and “Latin Hy- percube (LH)” sampling method is used as a tool to generate sample data, and both methods were compared. Finally Validation is conducted in order to propose an acceptable criteria of FP for single slope of sand...
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%.
Governing risk elements through open pit slope optimization
Journal of the Southern African Institute of Mining and Metallurgy, 2018
With the increasing competition in global mineral markets, designers are attempting to drive down overall mining costs. The demands for steeper pit slopes have triggered developments in the field of modern and comprehensive slope design. Risk-based optimization techniques are one of the most challenging state-of-the-art solutions for enhancing conventional procedures. Recognizing risk aspects has a fundamental role in updating the methods. Considering geotechnical and mine planning issues, this study describes the consequences of varying slope angles on final pit walls. Twenty-three risk elements are introduced and discussed in four groups: economic, technical, strategic, and regulatory compliance. Related examples are given on the state of the elements, and possible ways to achieve them from overall slope optimization studies of the Sungun copper mine in Iran. The circumstances indicate that decisions on optimized slopes do not relate only to geotechnical studies, but that relevant consequences depend on the four groups. Evaluation of the elements can promote slope optimization based on the concepts of risk. pit slope design, risk evaluation, slope stability, mine planning, Sungun copper mine.
The Open Construction and Building Technology Journal, 2020
Background: The construction and stabilization of deep excavations are associated with several uncertainties due to heterogeneous geological conditions. Therefore, the conventional methods of slope stability analysis do not provide reasonable results. Aim: Hence, it is logical to perform reliability analysis and also risk assessment to make a wiser decision under uncertainty for choosing the proper stabilization method of slopes. Methods: In this regard, a real case study, a 50-meter-deep abandoned open-pit mine, is considered. In the past, the studied deep excavation was located in a rural area, away from the important structures. However, due to the development of the city, the open-pit mine is now located in the city. Furthermore, the Kan River is located on the eastern side of the excavation. Deterministic analysis showed that that Factor of Safety is not sufficient for permanent condition; thus, the deep excavation may have destructive impacts on the adjacent structures and inf...
Economic significance of geotechnical uncertainties in open pit mines
2019
The major cost associated with open pit mine operations is waste stripping. While the steepening of slope angles reduces the stripping ratio, and hence operational costs, it also increases the likelihood of failure. Major slope failures incur significant cost elements including clean-up, disruption to mine operation, and damage to mining equipment and in some cases loss of reserves. Geotechnical engineers are often faced with the difficult task of finding the balance between slope optimisation and acceptable risk related to the likelihood of large slope failures. Technological advancements have allowed for the development of larger and deeper open pit operations, but have also created higher economic impact from potential slope failures. Given that the aim of mining operators is to maximise overall profits, it is surprising that most slope designs are based on deterministic design approaches, and limited attention is given to quantifying uncertainties in the geotechnical model. As most major decisions in the mining industry are made by senior management staff and financial staff, any attempt on linking slope stability analysis results with monetary values would improve the critical communication between geotechnical designers and decision-makers. Using Cowal Gold Mine as a case study, this paper illustrates economic risk caused by geotechnical uncertainties. The geotechnical risk estimate is generally subjective due to geotechnical engineers having to rely on limited data and engineering judgement. Geotechnical risk is compared against economic factors that are often perceived as important variables in mining operations.
Map of the potential geotechnical susceptibility for operational pit slopes
REM - International Engineering Journal, 2019
This article proposes a procedure to elaborate a map that presents the potential risk of failure occurrence in the operational slopes of open pit mines. First, it is necessary to collect the available geological-geotechnical data and perform a field mapping, in order to verify and validate the most representative parameters and to characterize the discontinuity families of the rock mass. Then, the mine should be sectorized, considering all the data collected, the geometry of the operational slopes and its development until the final pit. The next step will be to define and to evaluate which failure modes have greater or lesser potential to occur in the pit and to assign weights to them. In this study, the weathering, planar failure, and plane circular failure potentials were evaluated. As a result, it is possible to develop a map with the susceptibility level of the sectors. This map will help make technical and managerial decisions in order to reduce the risk level of the sectors and to promote an increase in the operational safety of the mine.