Principles of rock slope design (original) (raw)

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.

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

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.

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.

IRJET- Modelling and Design of Open Pit Slopes-A Case Study

IRJET, 2020

In Opencast mines benches are developed with certain inclination known as slopes. These slopes must be stable during entire life of the mine, thus facilitating further development of benches. Such maintenance of developed slopes without failures is known as Slope stability. The analysis for the study of such slopes is known as Slope stability analysis. These slopes can also be seen in dump areas. Failure of slopes causes deprivation of production, additional stripping cost for recovery and excessive handling of failed material, sometimes even burial of heavy machinery under the failed slopes. Thus proper design of slopes is needed to avoid its failure, using field experience, rules of thumb followed by sound engineering judgement. In the recent decades, more importance is given in designing stable slopes in Opencast mining operations. So, basic objective of the project involves: (a) Understanding the different types and modes of slope failures. (b) Modelling and design of open pit slopes by software approach. For modelling and design of open pit slopes GEO-SLOPE software is used, parametric studies are made by widely varying basic input values like cohesion, internal angle of friction, unit weight of the rock given to the software based upon design made in it. Thus finding factor of safety for the slopes and investigating failure mechanisms in them. Based on the significant studies, it can be concluded that as the slope angle increases factor of safety decreases. It is also concluded that as the Cohesion and angle of internal friction increases, the factor of safety increases. Recommendations for future work are given on the basis of designs.

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°