Optimal pitwall profiles to maximise steepness in anisotropic bedded sedimentary rock (original) (raw)
Related papers
Pit Slope Configuration for Open Pit Mining – A Case Study
American journal of science, engineering and technology, 2024
To achieve stable pit wall slopes, it is imperative to obtain a fair knowledge of the rock mass characterisation before designing the pit. Insufficient knowledge of the competency of the country rock could lead to using unsupported slope configuration in the design process which can consequently lead to slope failure. In this study, the geomechnical properties of the Bremen-Nkosuo concession are analysed using Bieniawski's classification scheme to determine the Rock Mass Rating (RMR) for defining safe pit slope configuration of the Nkosuo pit. The findings show that the rockmass are best described as 'fair' for the two main lithologies existing at the concession. Subsequently, localised adjustment factors are applied to the calculated RMR to arrive at Mining Rock Mass Ratings (MRMR). These MRMR values are correlated with 50 m fixed stack height and 1.2 safety factor to determine optimum Bench Slack Angle (BSA) of 54° and 57° for host sedimentary and granitic rocks respectively. For individual benches, optimum slope design configurations were 10 m, 800, and 6.6 m respectively for bench height, bench face angle and catch berm for metasedimentary rocks. Likewise, that for granitic formation were 10 m bench height, 800 face angle and 6.0 m catch berm width. These configurations are in conformance with mineral and mining regulations of Ghana. Slope stability assessment was performed which included Slope Mass Rating (SMR), Kinematic and Limit equilibrium analysis. From the analysis, multi-bench scale slope instability occurrence was found to be rare but single-double scale could be possible at the western wall of the planned pit with probability of failure of about 0.4. Presplit and trim shots perimeter blasting techniques are recommended to maintain the integrity of the final pit walls at certain areas.
SSIM 2023: Third International Slope Stability in Mining Conference
Geotechnical characterisation is generally carried out by subdividing a rock mass into a number of unique geotechnical domains, each exhibiting similar geotechnical properties. Geotechnical data for each domain are then analysed to develop representative parameters for each domain. This approach is not optimal for rock masses that have significant local-scale variability in geotechnical character. This paper documents the approach used to consider the high degree of spatial variability in geotechnical properties for the Lihir Mine, located in Papua New Guinea. The Lihir Mine is situated within the Luise volcanic crater, part of a volcanic island arc chain within the New Ireland arc-trench complex, southwest of an inactive subduction zone. The Luise volcano has previously been interpreted as a mafic to intermediate volcano, with an underlying porphyry system. Following volcanic sector collapse, the lithostatic load was rapidly decreased. This led to boiling of mineralised fluids and resulted in the formation of an epithermal gold deposit (Blackwell et al. 2010). Maar-diatreme activity then continued within the caldera, leading to the formation of diatreme eruptive centres and crater lake sediments. The geological history has resulted in a complex geological and structural environment with a high degree of geotechnical variability. Geotechnical characterisation has involved the use of geostatistical block modelling approaches to better identify the spatial variability of geotechnical properties within each geotechnical domain. The use of block modelling tools has allowed for greater resolution of input parameters for both 2D and 3D stability analyses.
Bench -inter-ramp -overall: A guide to statistically designing a rock slope
The proper design and evaluation of the catch bench angle, inter-ramp slope angle, and overall slope angle, individually as well as in combination, are required for successful excavation and economic optimization of a rock slope. In many slopes at least one, if not more, of the above controlling angles are essentially ignored, resulting in a slope properly designed for one facet of the excavation but ignoring the other components. Bench face angles can be accurately described statistically utilizing engineering predictions from the rock mass discontinuity network and discontinuity shear strengths. Together with the required bench width, the bench controlled inter-ramp angle is determined. Inter-ramp angles can be accurately determined by careful construction of a structural geologic model, noting location and orientations of discrete intermediate and large planes of weakness for the excavation in question. The location and orientation of the overall slope is dependent upon the slope as determined by the bench controlled inter-ramp angle and the stability controlled inter-ramp angle. Given advances in data collection and analytical techniques and continuing moves to increase mining safety while simultaneously attempting to minimize excavation costs, the only possible way to truly optimize slopes is through rigorous analytical methods combined with probabilistic techniques. 2 tan -1 (15m/(8m+(15m/tan(70°))) = 48° tan -1 (150m/(33m+(150m/tan(48°))) = 42°
Evolution of the pit slope design process at Western Mesquite Mines
2022
Open pit mining has been ongoing at Western Mesquite Mines since the early 1980s. This low-grade gold deposit is located in a structurally complex geologic regime of metamorphic rocks beneath up to 120 m of tertiary sediments ranging from silts to conglomerates. Original slope design angles were relatively steep, did not differentiate between the surficial and bedrock geologic units, and resulted in frequent slope instability events. Through a process of slope performance evaluations in historically mined pits, back-analyses of failures, rock mass quality mapping, and geotechnical drilling and laboratory testing, slope angles have been optimised for the geotechnical units encountered in the various pits at the mine. The Brownie Pit is the most recent pit to be designed and mined. The performance of the slopes in the Brownie Pit during the first phase of mining indicated that the design slope angles were appropriate, with one multi-bench instability in the rock and manageable deformations in the tertiary sediments. This case history outlines the evolution of the investigation and design process in this unique geologic environment, and illustrates how ongoing geotechnical characterisation and documentation of slope performance can deliver optimised slope designs, improved mining productivity and safer working conditions.
The Influence of the Methodology for Slopes Forming in Open Pit Mines on their Stability
IOP conference series, 2019
Open pit mines are frequently accumulating significant amounts of material in the form of dumping grounds, landfills or forming land for reclamation. Often the form of emerging dumping grounds is determined by stability analysis of their slopes at the design stage. During the operation of the mining site and the collection of material on the pile, only the geometry of the slope is a subject of control. In many cases, after making slopes of a dozen or so meters height or even up to several tens of meters, and after a certain time has elapsed since their formation, deformation of the escarpments can be observed. At this stage, the only option is to change the geometry, i.e. inclination of a slope or, in the worst case, rebuilding of the dump. In the paper the analysis of the impact of the method of forming slopes and material quality on stability of formed slopes and their safe exploitation has been presented. It also presents a proposal to normalize the methodology of design and construction of slopes in a manner ensuring stability and taking into account the variability of the material parameters from which the slope is to be formed.
Computer-aided optimal open pit design with variable slope angles
1999
Of these, the Lerchs-Grossmann algorithm is well known for being the only method which always yields the true optimum pit limit. However, the algorithm which utilises graph theory was based on fixed slope angles that are governed by the block dimensions when it was introduced. In spite of the fact that many attempts have been made to incorporate variable slope angles, none of them provide an adequate solution where there are, variable slopes controlled by complex structures and geology. This algorithm is reconsidered and modified to deal with variable slope angles. It is assumed that the orebody and the surrounding waste are divided into regions or domain sectors within which the rock characteristics are the same and each region is specified by four principal slope angles including North, South, East and West face slope angles. Consequently slope angles can vary through the deposit to follow the rock characteristics and are independent of the block dimensions. In addition, two methods were also developed to estimate the four principal slope angles from geotechnical information to use as input parameters in the optimal pit, design algorithm. A general PC software was also developed to determine the optimum pit limit with variable slope angles for an open pit mine. The software is a Windows application that'can be implemented under 32-bit operating systems such as. Windows 95, Windows NT and. Windows 98. It is capable of taking advantage of all the computer memory and designing the optimum pit limit for complex, large and low grade deposits due to solving the memory limitation. The software includes both graphical and numerical presentation of the, input data and the results of optimisation. Two case studies have been used to validate the software developed.
Three-Dimensional Analysis of Pit Slope Stability in Anistropic Rock Masses
Anisotropic and foliated rock masses, the behaviour of which are dominated by closely spaced planes of weakness, present particular difficulties in the assessment of pit slope stability. Various numerical modelling techniques are available that explicitly simulate the joints and discontinuities within an anisotropic rock mass. However, due to the computational intensity of these numerical techniques, it is not practical to explicitly simulate the joint fabric of an entire three-dimensional pit slope for routine stability assessment. In order to simulate the effects of anisotropic rock mass strength and deformation behaviour on pit slope stability, a modelling methodology has been developed to account for rock mass anisotropy and scale effects using a continuum based ubiquitous joint constitutive model. This paper outlines the anisotropic modelling methodology and presents a series of demonstration models that have been used to validate the technique.
Stability assessment and slope design at Sandsloot open pit, South Africa
Sandsloot open pit is located on the northern limb of the Bushveld Igneous Complex. It is the largest open pit platinum mine in the world. Three major joint sets have been recognized at Sandsloot, which are related to the regional tectonic history. They have an important influence on slope stability in the open pit, notably in terms of planar and wedge failures. Detailed geological and geotechnical data are often a notable unknown factor in the design and operation of an open pit, the lack of which may pose a significant risk to the mining venture. As data are accumulated and used effectively, so the risk of unforeseen conditions is reduced, and accordingly safety and productivity is increased. Usually, the geotechnical work undertaken at an open pit mine is in connection with improving slope stability. At Sandsloot open pit geological and geotechnical data have been obtained by face mapping, scanline surveys, from exploration drillholes and from laboratory tests. Such data have been used to delineate different geotechnical zones in which different types of slope failure have occurred. These are the usual types of slope failure associated with rock masses, namely, planar, wedge, toppling and circular failures. Analysis of the data has allowed optimum design parameters to be developed for these zones which has led to improved slope stability. In other words, this has allowed slope management programmes to be initiated, as well as slope optimization of the hangingwall. The latter resulted in an improved slope configuration and an increase in the ultimate angle of the wall by 71. This has resulted in substantial savings, as well as an improvement in safety. r
Optimisation of Slope Angles at Mine Rosario-Collahuasi
OPTIMISATION OF SLOPE ANGLES AT MINE ROSARIO-COLLAHUASI, 2006
The optimisation of slope angles, that is to say, increasing them, compared to the original design is always the subject of analysis of stability for geotechnical engineers and economic analysis for planning engineers. Questions to be answered include: • What is the acceptable risk? • What factor of safety? • What probability of failure or reliability? The Rosario Open Pit has a history of failure, poor quality rocks and high pore pressures. It was decided to deepen the pit below the programmed design to test the practicality of different design approaches, which if successful, could be used to improve the economics of mining at Collahuasi. The revised slope design has factors of safety in the range of 1.0 to 1.2, probabilities of failure of ten to 38 per cent, and increased slope angles of between 3° and 5° with respect to the original design. The pit deepening with these design slopes will deliver an extra two million tonnes of ore which will have a significant positive impact on mining economics. ROSARIO MINE-COLLAHUASI LOCATION The Rosario mine is located within the Collahuasi District, approximately 180 km south east of the city of Iquique in the Mountain I region of Chile, at an elevation of between 4300-4800 m.s.n.m. The Rosario deposit is principally primary sulfides, with a poorly developed secondary enrichment horizon that deepens between 50-250 m, strongly controlled by faults (Munchmeyer, 1984) (Figure 1). The orebody extends 2 km NW-SE and 1.5 km NE-SW and is continuous to a depth of more than 600 m below the sulfide interface.