THE BENEFIT TO OPEN PIT ROCK SLOPE DESIGN OF GEOTECHNICAL DATABASES (original) (raw)
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Geotechnical applications in open pit mining
Geotechnical and Geological Engineering, 2001
Detailed geotechnical data is often a major unknown factor in open pit design and mining, the lack of which constitutes a significant risk in any mining venture. As geotechnical data is accumulated so the risk of unforeseen conditions reduces, and so safety and productivity can be increased. Previously, most geotechnical work undertaken at open pit mines has focused on the slopes. The work done at Sandsloot open pit situated on the northern limb of the Bushveld Complex, 250 km north east of Johannesburg, however, has involved using geotechnical data for production, as well as slope stability benefits. Solutions to production problems encountered in a rapidly developing open pit are best formulated once some geotechnical control at the pit has been attained. At Sandsloot open pit this was achieved by delineation of geotechnical design zones from a detailed face mapping and drilling programme. Optimum design parameters then were assigned to these zones and geotechnically related problems assessed. This 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 7°. This resulted in substantial savings, as well as an improvement in safety. In addition, the zones can be used for planning, costing and pit scheduling. The methods have proved successful in optimizing blast fragmentation and thereby loading, crushing and milling rates; in reducing secondary blasting and improving floor conditions; and in reducing drilling, blasting and comminution costs.
2020
This paper presents the Geotechnical Workbench software that was developed by a working team in BHP Iron Ore with the intention of providing an integrated tool to the geotechnical team that permits consistent decision-making of strength properties for slope design. This paper includes a description of the steps taken for software development and the list of learnings gained by the working team. This information is shared for the wider industry for the benefit of others that may endeavour a similar initiative. The software architecture is presented in a very minimalistic manner to protect intellectual property, however, the paper still shows the general idea of software functionalities including some description for the major tools developed within the whole package.
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.
Correlations of geotechnical monitoring data in open pit slope back-analysis -A mine case study
The Journal of the Southern African Institute of Mining and Metallurgy, 2021
Geotechnical monitoring plays an important role in the detection of operational safety issues in the slopes of open pits. Currently, monitoring companies offer several solutions involving robust technologies that boast highly reliable data and the ability to control risky conditions. The monitoring data must be processed and analysed so as to allow the results to be used for several purposes, thereby providing information that can be used to manage operational actions and optimize mining plans or engineering projects. In this work we analysed monitoring data (pore pressure and displacement) and its correlation with the tension and displacement of the mass of an established failure slope calculated using the finite element method. To optimize the back-analysis, a Python language routine was developed using input data (point coordinates, parameter matrix, and critical section) to use software with the rock mass parameters (cohesion, friction angle, Young's modulus, and Poisson's ratio). For the back-analysis, the Mohr-Coulomb criterion was applied with the shear strength reduction technique to obtain the strength reduction factor. The results were consistent with both the measured displacements and the maximum deformation contours, revealing the possible failure mechanism, allowing the strength parameters to be calibrated according to the slope failure conditions, and providing information about the contribution of each variable (parameter) to the slope failure in the study area.
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.
Geotechnical data – a strategic or tactical issue?
2011
Newmont uses a Stage-Gate approach to developing mining projects which takes a project from scoping (Stage 1) through to implementation (Stage 5). This is linked to the resource and reserve conversion process as well as confidence in mine designs and planning. The question of how much geotechnical data is needed at each stage often arises. Currently very little quantitative guidance exists in the literature although there have been attempts by various authors (Haile, 2004; Haines et al., 2006; Read and Stacey, 2009) to qualitatively describe what level of geotechnical data is required. Each mining project is different and the data collection program should be designed to reflect the orebody type, possible mining methods, appetite for uncertainty and the owners risk profile. In all cases a number of key questions need to be considered: An approach has been developed that attempts to define what levels of geotechnical data are required to support the Stage-Gate process, and examples a...
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.
Geological control on slope failure mechanisms in the open pit at the Venetia Mine
South African Journal of Geology, 2003
The Limpopo Belt is a complex accretionary terrane that has undergone numerous deformational events. Tectonically juxtaposed lithology, open to isoclinal folding, cross-cutting and re-activated shear zones, and closely interlayered metamorphic gneisses and schists make pit slope design and maintenance risky. Pit slope design effects the stripping ratio and the "bottom-line" profitability of a mine. The geological model is the basis on which a pit design starts. At Venetia Mine the model is a tight, northward verging syncline that plunges shallowly towards the east-northeast. The geology has been modeled three-dimensionally using GEMCOM software. The jointing patterns have been studied and hypothetically related to the geology. The synform fold model implies three major pit slope design sectors, the (a) southern limb, (b) fold hinge zone and (c) northern limb of the fold. The southern limb experiences predominantly planar failure, a problem that has resulted in a reduction in the pit slope angle from 51 o to 37 o and 44 o in two of the southern domains respectively. The northern limb undergoes bench-scale toppling and wedge failure. The hinge zone suffers only from local wedge failure. Bench-scale folding and brittle faulting have created more local problems. Some faults create large slope-scale wedge failures. These geological variations and the relative orientation/position of the excavation necessitated the definition of a total of 11 geotechnical domains, each with an individual pit slope design. The improved understanding of the geology and its impact on the rockmass behaviour will lead to improved blasting practices and steeper slope angles.
Geodatabases to improve geotechnical design and modelling
ce/papers, 2018
Geotechnical designers and modellers must capture and quantify the variability of key soil properties to make engineering decisions. There is a long history in geotechnical engineering of assembling large databases of past soil tests. This paper shows the use of geotechnical databases in two contexts: (a) slope stability modelling in the Eastern Caribbean and (b) settlement response of bored piles in London Clay.
Using a structured data management system to improve mine development efficiencies
Proceedings of the Fourth International Symposium on Block and Sublevel Caving, 2018
A structured data management system has shown measureable improvements during two years of data capture, management, and analysis at the Oyu Tolgoi underground mine. This has directly led to enhanced contractor relationships between the mining contractor and the owners team, and underground development quality. CaveCad is an integrated data capture and storage system for capturing underground block caving related data. The CaveCad system has been used in conjunction with detailed data capture, through laser scanning of every excavated development round. This is undertaken immediately after mucking and then again directly following the installation of ground support. This results in detailed 3D as-builts which are used for measuring a number of quality control metrics including resin encapsulated rebar and cable bolt spacing, mesh overlap, shotcrete thickness, and excavation compliance to design. The data collected from this process is used for tracking compliance to both excavation and ground support design, and, where required, rectification of issues by the contractors when installations are non-compliant. In the past, serious safety incidents have occurred in the mining industry due to a lack of detailed understanding of the true as-built of the mine, along with a lack of understanding of the history, location, and quality of installed ground support material. The strategy of keeping a specific team for data management and analysis was directly related to the decision to laser scan all blasted headings underground, to mitigate these potential risks and knowledge gaps, and to ensure high-quality usable data is available throughout the mine life. A detailed 3D as-built plan is available for both the excavation and installed ground support, which can be referenced at all times by all mining personnel. The results of this detailed data capture show improvements over time in both quality and efficiency of the mining process. This includes a reduction of shotcrete overspray and over-bolting issues and a marked decrease in excavation overbreak from the designed tunnel profile, resulting in an increase in compliance to excavation design. This has enabled Oyu Tolgoi to improve accuracy of mining, quality of the ground support installation, reduction in wastage (e.g. shotcrete), and improved, better informed discussions with contractors regarding key performance indicators that incentivise them. High-quality and qualitative data management has also allowed for fast and reliable data sharing between stakeholders, reducing any potential knowledge silos and enabling improvements to be made to the mining cycle based on actual lessons learned.