Pit Wall Stability Research Articles

Numerical modelling of the pit wall stability while optimizing its boundaries to ensure the ore mining completeness

Purpose is to assess changes in the stress-strain state of walls along the whole periphery of a super-deep open pit while optimizing its current and final boundaries for the complete ore excavation. Methods. Finite element 3D analysis of stress-strain state (SSS) of the soil and rock mass relies upon the models varying in their scales. Macrolevel model includes the full pit helping perform initial evaluation of its stability depending upon changes in the general wall slope along the pit periphery. Then, the macromodel is separated into sectoral models with smaller scales oriented radially in such a way to include potentially unstable wall areas. The sectoral models make it possible to show the complex bench line in more detail after the peripheries were optimized in terms of economic factor and simulate layered structure of the rock mass. Elastoplastic model of the medium as well as Mohr-Coulomb strength criterion has been implemented using RS3 (Rocscience) program codes. Findings. An indicator of wall strength (safety factor) distribution along the pit periphery has been identified; potential sliding surfaces within each of the separated open pit sectors have been localized based upon the shear strength reduction (SSR) procedure. Influence by the general wall slope as well as by the indicator of the ore excavation completeness on the stripping ratio has been demonstrated. Originality. For the first time, two-level modelling has shown difference in a safety factor depending upon a model scale and a reflection degree of the soil-rock mass structure. In the context of the actual mining and geological conditions of Kacharsky open pit, changes in the safety factor along the pit periphery have been identified depending on the general slope of the wall. Practical implications. Based upon the pit wall stability along the whole periphery, the possibility has been substantiated to optimize its design boundaries for the excavation of those amenable ore reserves, occurred near them, inclusive of ore, occurring in a bottom, which mining is impossible due to inaccessibility.

Комплексный анализ результатов мониторинга устойчивости уступов карьера с использованием геофизических методов исследования

The Response to challenges related to safety in open-pit mining of mineral deposits is based on continuous monitoring of the pit wall stability as a whole as well as the stability of problematic areas of the pit wall and individual benches. Control of the geomechanical state of the adjacent rock mass using local geophysical methods plays an important role in the overall monitoring of stability of the open-pit elements. The control allows studying in more detail the state of benches and groups of benches in critical areas of the open-pit and developing measures to ensure production safety on this basis. One of the main interdependent factors affecting the pit wall stability is, on the one hand, the size of the disturbed zone that depends on both natural and mining-induced rock fracturing; on the other hand, the level of ground water changing over time depending on the season. The importance of joint account of the factors above has stipulated to propose a comprehensive methodical approach to study water saturation and structural disturbance of rocks in the wall of a deep open-pit. The method consists in periodic, seasonally synchronized, geophysical studies using seismic profiling and GPR sounding and allows identifying the areas of high water saturation and disturbance in the adjacent rock mass. The methodological approach makes it possible to estimate the effect of the main time-varying impact factors (water saturation, natural and mining-induced disturbance, anomalies of physical properties of the rock mass) on the slope stability and provides a scientific and technical basis for developing engineering measures to improve the safety of deep open-pit mining.

Adjustment of slope geometry in Urtui open pit mine toward pitwall stability using numerical modeling

Adjustment of slope geometry in Urtui open pit mine toward pitwall stability using numerical modeling

Studying rock mass jointing to provide bench stability while Northern Katpar deposit developing in Kazakhstan

Purpose is to identify the basic joint systems, their characteristics, distribution within the rock mass, and determine impact of the joints on the bench stability. Methods. The risks of strain emergence in the form of blocks sliding along weakness surfaces within the local areas were determined based upon the definition of rock stability loss. The results of large-scale measurements of jointing were processed using circular and bar diagrams as well as stereographic grids. In the context of the paper, kinematic analysis was implemented through Dips Rocscience Inc. Software. Findings. Five basic joint systems have been identified; joints of 2nd and 5th systems are the most commonly encountered among them. The results of the jointing determination within the open pit boundaries have been represented as well as the open pit wall stability in terms of each site inclusive of consideration of potential strains along the sliding surface. Originality. For the first time, zoning of the open pit wall in terms of slide types has been performed. It has been identified that potential shear of a prismatic block is 33%; at the same time, 66% are bench destruction with the block toppling. The risk of wedge-shaped block shear is minimal. Practical implications. The research findings may be helpful to define and select both parameters and conditions of safe mineral extraction under the specific mining and geological conditions. In turn, the abovementioned will help reduce the risk of accidence while providing scientifically substantiated approach to select quarrying sequence, techniques, and system.

TRANSITION FROM OPEN PIT COAL MINE TO THE UNDERGROUND MINE IN SOFT ROCKS

To achieve a successful and effective operation, the transition from open pit to underground mining requires accurate planning and analysis. Numerical modeling utilizing programs like FLAC3D has been an important tool for simulating and analyzing the complicated geomechanical behavior connected with this shift in recent years. The use of FLAC3D to develop a model for the switch from open pit coal mining to underground coal mining in soft rocks with using room and pillar mining method is explored in this abstract. It presents the development of model to analyze and simulate the complex dynamics of this transition. The significant considerations that went into developing the model, such as geotechnical characteristics, rock mass behavior, and mine design parameters, are highlighted in the abstract. It highlights how essential proper input data are to producing reliable simulations and forecasts in soft rocks. The usage of FLAC3D for tracking pit wall stability during the transition period, evaluating the influence on nearby infrastructure, and optimizing underground mine design are covered in the abstract. The models flexibility allows the investigation of various conditions and offers valuable insight about the transition process. The research emphasizes the potential of the FLAC3D model to lead decision-making during the transition from open pit to underground mining through detailed analysis like choosing appropriate width for main entrance and cross section stopes and their interpretation. It emphasizes how important it is to understand the geomechanical behavior of the coal deposit, optimize the mines design parameters, and ensure safety for employees. The room and pillar method is utilized to recover coal resources from deep underground mines, and the results from the model can help improve efficiency, sustainability, and risk prevention. KEYWORDS: Underground mining, Open pit mining, Room and Pillar mining method, FLAC3D, Coal mining, Soft rocks.

Reliable prediction of geotechnical risks in open pit mining

The currently required minimization of geotechnical risks in open pit mineral mining includes timely prediction of slope failure probabilities and their impacts on personnel, environment, equipment, infrastructure and production efficiency of mines. The main tool to predict stability of pitwall slopes in modern geomechanics of rocks is the numerical modeling greatly dependent on the reliability of the source data. The risk prediction reliability is in focus of this study. It is preferable to use the notion “failure probability” as the criterion of pitwall stability as the uncertainty of parameters has already been determined quantitatively in this case. With the notion “stability factor” used as the stability criterion, it is required to add the calculated stability factor with the degree of variability of the initial parameters, with an emphasis on the reliability of geotechnical data. The reliability of the pitwall stability estimation largely depends on the geotechnical data reliability. The projects at the stage of a mineral field development should have the confidence level of data not lower than 80 %. The point rating system is presented for the estimate of the geotechnical data reliability. The procedure has been tested at some deposits at different project stages, and has proved to be handy, simple and objective. Using the described assessment system of the data reliability, the actual “standard” values of the stability factor are obtained for some open pit mines in operation and under design.

Tectogenesis as a factor influencing the stability of rock masses of the Northern iron ore district of the Kryvbas


 
 
 In the Northern iron-ore district of the Kryvbas basin, mining of deposits of poor magnetic ores is underway in two quarries – Pervomaiskyi and Hannivsky. Oftentimes, their mine contours contain low-valuable or unusable magnetite-silicaceous quarzites of containing ferrous and slate horizons. As a result, excavated ore mass contains ores and partly containing rocks of various mineral and chemical compositions and physical and technical properties. This caused diversity (15 mineral kinds) of the compositions of ores mined from the both deposits. Variability of mineral compositions of ores and rocks is due to manifesta- tions of numerous geological processes such as sedimentation, metamorphism, tectogenesis, metasomatism, supergene, etc. Various mineralogical, geochemical courses of the processes resulted in variability in physical, technical characteristics of ores and containing rocks, and this, in turn, caused various stability of rock masses during drilling-explosive works and mining. Stability of pit walls of the quarries of iron-ore deposits of the Kryvyi Rih basin is a sharp issue for mining enterprises. Solutions to those issues have been analyzed in various aspects. A number of factors take effects on the indicator of stability of rock masses within deposits, particularly mineralogical, geochemical, tectonic, etc. This paper looks at the influence of the tectonic factor specifically, which actively manifests within the Pervomayskyi and Hannivskyi deposits as fractures, breccias, mylonite of ores and rocks. During the surveys, there were designated tectonically altered kinds of ores and rocks within the both deposits, which take effects on seismic stability of pit walls of the both quarries, and also we put areas with various tectonic intensities on schematic maps. For this purpose, we used geological methods of study (selection of samples, mapping), mineralogical (determining quantitative proportions of minerals, texture, structure of ores and rocks). The study provides the data of mineralogical estimates of tectonically altered types of ores and rocks of productive layers of the Pervomaiskyi and Hannivskyi deposits of the Kryvyi Rih basin. We charted maps with areas of various manifestations of tectonic changes within productive layers of the both deposits.
 
 

Mathematical modeling the quarry wall stability under conditions of heavily jointed rocks

Purpose. To develop techniques for estimating the pit wall stability in terms of occurring of a zone of heavily jointed rock mass during ore mining at the Akzhal deposit (Kazakhstan), to work out measures to strengthen the rock opening and to verify the effectiveness of the developed measures. Methodology. The finite element analysis of the rock stress-strain state is implemented on the basis of the elastic-plastic model and the generalized Hoek-Brown failure criterion. The rock mass quality was assessed using the RMR and GSI rating classifications. This made it possible to simulate a zone of intense fracturing by changing the characteristics of the jointed surface. The shear strength reduction procedure was used to determine the safety factor for the quarry wall. Findings. The strain distributions in the rock mass forming the quarry wall have been obtained in terms of the Akzhal polymetallic ore deposit (Kazakhstan). The case of creating a zone of heavily jointed rocks in the area of a tectonic fault was considered. The safety factor of the quarry wall was determined under conditions of increased rock fracturing, as well as after carrying out measures to strengthen the rocks with a hardening solution. Originality. The effect of intense jointness on the pit wall stability is demonstrated. A method for the consistent evaluation of the quarry wall stability is proposed considering the change in the rock properties due to natural factors and artificial reinforcement. It is shown that a change in the joint surface quality due to the hardening injection reduces the shear strains in the sliding zone. Practical value. The pit wall stability was predicted considering the formation of a zone of intense fracturing under mining and geological conditions of the Akzhal deposit. The possibility of testing the effectiveness of rock strengthening measures based on mathematical modeling was shown.

Improving the pit wall seepage resistance at the V. Grib diamond deposit

Introduction. V. Grib deposit development includes complex dewatering operations, all water-bearing rocks overlying the mining floor are drained. The open pit is mainly flooded by the Padunsky aquifer system. At present, the open pit is being drained by surface dewatering wells together with mine drainage. In total about 7–8 thousand m3 /h of drainage water is pumped out. Setting of the problem. Uncovering a multilayer water-bearing strata characterized by different filtration characteristics of rocks contributes to the formation of pit walls in the Padunsky strata that have not been dewatered. The height of groundwater seepage on pit walls reaches 50 m due to the low conductivity of the Padunsky strata bottom. It is suggested that the Padunsky strata bottom should be dewatered using lateral drain holes built from the pit to the wall benches in areas with no dewatering wells. Methods of research. For pit wall stability improvement, the developed multilayer numerical model of geofiltration is applied to study the use of lateral drain holes built from the pit. The finite difference method in the GMS MODFLOW package was applied for modelling. Research results. It has been found that the operation of 12 lateral drain holes during 1 year reduces the height of groundwater seepage on pit walls by 15–20 m, contributes to the groundwater level decline of the Padunsky aquifer system by 5–10 m on the drainage contour of dewatering wells; water inflow to lateral drain holes will be 810–850 m3 /h. Conclusions. The feasibility of lateral drain holes for the Padunsky strata dewatering intensification in the adjacent rock mass has been established using the method of numerical modeling.

A Multilevel Approach to Pitwall Stability Monitoring

A Multilevel Approach to Pitwall Stability Monitoring

Predictive assessment of the stability of quarry sides

The composition of the rocks composing the quarry sides and the approximate slope angles in accordance with the mining and geological conditions are described. The issues of creating observation stations are considered taking into account seasonal temperature fluctuations of the benchmarks. Observation materials are generalized, the degree of danger of deformations is established on the basis of observations of deformation speed. The mining safety control methods are described. The disadvantages of the approach to data processing and analysis are identified. A criterion for mine surveying prediction of the pit wall stability based on the comparison of critical and actual relative deformations is proposed. The purpose of the local forecast of wall deformation is to control the stability of non-working and working slopes of the sides, and to confirm the efficiency of the method used. The predictive assessment was carried out on the shift of working benchmarks on one of the open pits of Transbaikalia. It is suggested monitoring the stability of rocks using oscillograms obtained by seismic equipment.

Geomechanical substantiation of the northeastern pit wall stability in Kurzhunkul mine

Kurzhunkul magnetite deposit is located in the Kostanai Region of Kazakhstan and is an open pit mining project of Sokolovsko–Sarbay Mining and Production Association (SSGPO) since 1983. The current depth of the open pit is 240 m (Level -28 m). It is expected that Kurzhunkul pit reaches the depth of 290 m. The deformation determinant in Kurzhunkul mine is its geological structure represented by complex faulting. Special care and attention should be paid to the northeastern pit wall which is a zone of large and closely spaced tectonic faults essentially extended along the strike and dip of the deposit, and depthward the pit. Unfavorable bedding conditions in combination with weak physical and mechanical properties of fracture fillers can induce movement of rock blocks during extraction of mineral reserves from the weak zone of the northeastern pit wall. This study offers the geomechanical substantiation of stability of NE Kurzhunkul pit wall which is most heavily intersected by tectonic faults and has low strength characteristics. The study was carried out with grant financing in framework of Project No. AR08053358 Rock Mass Control Based on the Integrated Geomechanical Model toward Mining Safety.

Assessing the impact made by groundwater processes and undermining on coal pit wall stability

Introduction. The reliability of geomechanical prediction depends on the level of detail of databases covering geological structure, geometry and physical properties of the rock mass under investigation. In order to improve the accuracy of coal pit wall stability prediction, following the generalization of databases containing geological survey, groundwater monitoring, geophysical sounding and mine surveying, it is advisable to construct three-dimensional geological-geophysical models accounting for the main adverse factors, and thereafter search for the most hazardous section. Research aim is to predict wall stability according to the developed algorithm based on the threedimensional geological-geophysical model. Research methodology includes a search for the most hazardous rock mass site section by the ratio between shear and retaining forces within the established zones with anomalous physical characteristics. Results. By generalizing databases containing geological studies, groundwater monitoring, geophysical sounding by the method of electrical resistivity tomography, and mine surveying, a three-dimensional geological- geophysical model has been constructed of a wall loaded with “heap of dry rock atop of the hydraulic dump” man-made structure and undermined by underground works. The trial site stability has been predicted for the true state of mining. Comparative analysis of the obtained data has been carried out. Summary. The combination of natural and man-made factors, including hydrogeological conditions of the territory, seasonal and climatic behavior, tectonic faulting of the deposit and shear zones connected with undermining result in the development of a rather complex geological structure of the wall which includes local deconsolidated and waterlogged zones significantly reducing the stability of the pit slope. At the trial site of Kedrovsky pit due to spatial and temporal alternation of properties and state of rock within the landslide hazardous zone, the variation range of the factor of safety in six typical sections amounts n = 1.06–2.39. For that reason the objective prediction of slope stability in similar conditions (in addition to geological survey and hydrogeological observations data analysis) should include geophysical monitoring of anomalous zones origination and development, hereupon creation of a treedimensional geological-physical model, and the automated calculation of the factor of safety including repeated selection of the most hazardous section.

Landslide stabilization experience in Urtui open pit mine

Instability of pit wall slopes is the most critical accident in open pit mining. The risk of damages to pit walls is proportional to the height of exposed surfaces and to the time of exposure. Among many factors governing pit wall stability, the major factor is geological structure and weakening zones in rock mass. Deformation processes are initiated in host rock mass of coal seams mostly because of undercutting of weak interlayers. Alongside with local undercutting, another cause of landslides is transition of coal mining from down-dip extraction to up-dip extraction. The sequence of mining and morphology of weak interlayers also have influence on initiation and evolution of deformations. The basic component of engineering solutions on pit wall stability control is optimization of mining sequence and methods of accessing working horizons in open pit mines. Large-scale deformation of Western and Southeastern pit walls in Urtui mine could be avoided using the optimized sequence of mining operations. For example, mining advance mostly along the curve of the Urtui centroclinal fold, with early access and destress of the eastern and, first of all, western wings of the fold could make it possible to evade from up-dip mining of coal seams and, as a consequence, to solve the major geomechanical problems in the open pit mine.

Moderate blasting technologies: Experience and prospects for introduction in Polyus mines

It is commonly known that rock fragmentation by blasting is the most economically efficient method to prepare large volumes of rock mass to excavation and handling. The drilling and blasting technology accepted by a mine governs both rock fragmentation quality and mining safety connected with slope stability. Therefore, optimization of drilling and blasting is an objective calling for the effective blast design and control. This article presents the main principles and methods of moderate blasting implemented at Polyus company towards minimization of impact on pit walls and benches. The main point is stagewise reduction of the dynamic effect exerted by blasting on rock mass when approaching the ultimate pit limits. Polyus company initiated the far and wide review and introduction of the best international practices for improvement of blasting operations near the ultimate pit limits. The article describes the activities undertaken within implementation of projects on drilling and blasting technology justification and improvement to enhance stability of pit walls and, as a consequence, to reduce geotechnical hazards. As a complimentary measure to abate seismic effect of explosions on adjacent rock mass, the nonelectric blasting is replaced by electronic blast initiation systems with more accurate delay intervals, which almost nullifies probability of simultaneous ignition of two or more charges and ensures, thereby, the acceptable and seismically safe modes of blasting of large rock blocks. Furthermore, the introduction of the electronic blasting cardinally changes the approach to blasting order and sequence per intervals in blast holes depending on the current task within a block to be blasted.

Numerical simulation of the open pit stability based on probabilistic approach

Purpose. To identify development regularities related to a stress-strain state and stability of the open pit walls while mining the steeply inclined iron-ore body at various stages of mining considering deterministic and stochastic components of the rock mass structural heterogeneity. Methodology. Numerical 3D simulation of the rock stress-strain state; application of the strength reduction procedure to determine a safety factor, taking into account the rock mass heterogeneity based on a stochastic model. Findings. The distribution of maximum shear deformations and displacements within the rock mass, making up the pit wall, has been obtained. Potential slide surfaces and safety factors have been determined at various stages of the inclined ore body mining. The effect of the rock mass structure on the pit wall stability has been estimated. A comparison of calculations based on the 3D and 2D models has been carried out. The correction coefficient has been obtained, which allows using the 2D model for multivariate calculations. The relationship of safety factor versus the overall slope angle has been developed. Originality. It has been proved that pit walls retain their stability (the stability factor (SF) is not less than 1.27) while mining the steeply inclined ore body with the transverse panels from top to bottom within each newly cut layer, despite the increasing depth of mining. It is shown that modeling of the real geological structure of a three-dimensional rock mass area factors into the decrease in (by 7%) the safety factor in comparison with the results of the homogeneous model. A probabilistic-statistical approach has been proposed to consider the heterogeneity of the rock mass and avoid unreasonably optimistic forecasts of the pit wall stability. It is shown that 3D modeling gives SF, which differs by 8% from the values obtained in the 2D model. This allows substantiating the correction coefficient to improve the 2D modeling results. Practical value. The regularity of changes in the pit wall stability has been determined depending on the overall pit slope angle in terms of mining-geological and mining-technical conditions of the Kachar deposit, taking into account the real rock heterogeneity.

Analysis of 2D and 3D estimates of pit wall stability

Analysis of 2D and 3D estimates of pit wall stability

The analysis of computer aided methods applied for pit wall stability rating

A comparative analysis of the results of the pit slope stability rating carried out under normative technique and Scad Office Slope application is presented. The possibility of combination of normative technique and computerized calculations to gain integrity and computation operability is suggested.

Effect of Blast-induced Ground Vibration on Factor of Safety of Pit Wall Stability

The regulated maximum peak particle velocity (PPV) from blasting operations of an open-pit coal mine is less than 2 mm/s to prevent mainly any public disturbance such as ground vibration and air blast. However, the blast-induce ground vibration can also decrease the stability of pit slope, which has not been intensively studied. A claystone pit wall, which is geotechnically investigated as having a plane failure type and the natural condition factor of safety (FS), has been selected for this study. The FS is selected to measure the effect of blast-induced ground vibration on the slope stability. The limit equilibrium, pseudo-static 1 (), and pseudo-static 2 () methods are used to determine the FS. The vibration results of blasting monitored at three slope positions: crest, middle, and toe, from two areas at the same pit wall, are recorded by blasting seismographs. Maximum charge weight per delay and the distance from blast areas to seismographs are collected to construct the scaled distance. The percentage change of FS of three methods from both areas compared to natural condition FS are all less than 4 percent considered that the slope stability is safe from blasting vibration (less than 15 percent). The relationship between the FS and maximum PPV from the limit equilibrium, pseudo-static 1 (), and pseudo-static 2 () methods indicate that the adverse maximum PPVs given the unity FS are 16.60 and 4.58, and 4.74 mm/s, respectively. The regulated PPV less than 2 mm/s at the mine is reasonable to prevent any possible plane failure. However, many impact parameters have not been included in this study, and their effects may disturb the pit wall stability.

Probability assessment of pit wall stability in jointed rock mass

Probability assessment of pit wall stability in jointed rock mass