Open Pit Walls Research Articles

Substantiation the safety open pit wall parameters in the conditions of a reduced protective zone near State critical infrastructure

The research is focused on topical issues of determining the safe parameters of pit edges in the conditions of a reduced protective zone near a critical infrastructure facility. Considering the extraction of soft rocks that are prone to landslides and deformations, the permissible safe distances from the upper edge of the pit on the surface to the industrial infrastructure facility are determined and established. Based on the physical and mechanical properties of the rocks, the parameters of geomechanical models of the pit edges were developed and substantiated to study their stability and stress state in the conditions of the Eastern section of the Chabanivske clay deposit. A brief description of the deposit under study and its geological structure is given. Computer modeling was carried out to determine the safety factor, and changes in the stress state of the massif near the pit edge were determined by the finite element method. Taking into account the mining technology were determined the safe parameters of the pit edges. Safe distances from high-pressure pipelines of state importance are substantiated. A rational pit edge angle of 28 – 31 degrees is recommended, and the appropriate safety distance for the rocks of the Chabanivske deposit in the western section should be at least 95 m.

Substantiation of the Direction for Mining Operations That Develop under Conditions of Shear Processes Caused by Hydrostatic Pressure

This research is aimed to substantiate the optimally safe direction for mining operations developing in the conditions of shear processes under hydrostatic pressure influence when mining the Zavalivskyi Graphite Deposit. Using a graphical–analytical method, the slope stability index of the Pivdenno–Skhidnyi open-pit walls in the Zavalivskyi deposit and the safe distance for placing mining equipment have been determined. This method involves constructing a calculation scheme for each studied open-pit wall area based on the determined parameters by algebraically adding forces along a curvilinear shear surface, taking into account hydrostatic pressure within a possible collapse prism. During the research, factors have been identified that influence the optimal direction for stripping and mining operations developing under conditions of shear processes caused by flooding of lower horizons at the Zavalivskyi Graphite Plant. It has been revealed that the determining factor when choosing the direction for the development of mining operations is the safety factor of the open-pit working wall, ranging from 0.9 to 2.71 in the studied areas. Moreover, according to current normative documents, this indicator should not be less than 1.3. It has been determined that a promising direction for the development of mining operations in the Pivdenno–Skhidnyi open-pit mine is its south-western, western, and north-eastern areas, with a length of 556 m and a safe size for placing mining equipment of 27.12–32.54 m. Recommendations and measures for conducting mining operations have been developed to ensure the stable condition of the open-pit walls.

Fiber-Optic Sensor for Stability Control of Open Pit Walls

Fiber-Optic Sensor for Stability Control of Open Pit Walls

Изменение потока сейсмической энергии при переходе на глубокие горизонты (месторождение Апатитовый Цирк, Хибинский массив)

The study is aimed at assessing the changes in seismic energy flow as mining operations advance to deep levels as exemplified by the Apatite Circus apatite-nepheline deposit (Khibiny Massif), which underground reserves are difficult to develop due to the presence of the nearby Rasvumchorr Plateau deposit, which is mined using the open-pit method. Underground mine workings and open-pit walls are located in the bordering area. A large number of fractures and tectonic faults are exposed in this area, which become waterlogged when the snow thaws. As a result, the stress-and-strain state of certain rock mass sections (mainly the tectonic fault zones) changes, which generally affects the seismic settings of the deposits. Along with transition of the mining operations to greater depth, an increase is observed in the number of seismic events and their energy in the lower levels of the mine. Also the fracturing processes in the overhand part of the rock mass are reflected in seismicity activation. The paper presents maps showing the spatial distribution of the seismic energy flows of various events across the mine field as mining progresses to greater depth. It has been established that there exist areas of increased level of seismic energy flow distribution, corresponding to the compressive strain zones (two lower levels, where intensive mining is in progress) and tensile strain zones in the overhand part of the rock mass ( the top third layer), where a gradual collapse of the near-surface area of the mass occurs.

Влияние статической нагрузки от горнотранспортного оборудования на устойчивость уступов, расположенных в скальных породах

Most of the enterprises applying open-pit mining method at deposits face challenges of pit wall steepening when approaching the pit wall to the final position or reducing productivity. The main task when increasing the angle of pit slope is to determine its stability. One of the ways to steepen the open-pit wall is to increase the slope angle of benches composing the open-pit wall. The bench stability is primarily determined by its physical properties and structural uncertainty. The higher the strength properties of rocks, the steeper the slope angle formed in these rocks can be. The "Rules of stability..." provide for the possible accounting the loads from mining equipment when assessing the stability, but this possibility is provided for the calculation of bench stability of open-pits and cuts, formed by semi-hard and dispersed rocks, dumps formed from clay or semi-hard rocks and (or) from a mixture of clay and hard rocks. At the same time, it is of interest to assess the impact of static loading from the located mining transport equipment in a stationary state on the stability of the benches located in hard rocks. It is shown that the load from the track dozer scraping the berms has an impact of no more than 6-7% for a distance of about 15 m from the top crest of a 30-meter long bench with a slope angle of 80° to the edge of the track, which is generally insignificant for maintaining bench stability. The minimum value of the safety factor of the bench with the load from the BELAZ-75306 mining dump truck is at a distance of 8 to 10 m from the top crest to the edge of the wheel. That is, at this distance the mining dump truck has the maximum impact. At 30 m distance from the bench’s top crest, mining dump truck has no impact on the bench stability. The maximum impact of the dump truck on the stability is 22 to 25%.

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.

DETERMINING THE MAXIMUM HEIGHT OF IMPACT OF THE NATURAL MOUNTAIN SLOPE ON THE STABILITY OF THE OPEN-PIT WALL

By implementing 3D physical modeling investigations, the maximum height of the non-exposed mountain slope extending over the last bench of the open-pit overall slope in loading conditions, as an example of the South-West wall of the Qajaran open-pit mine “Zangezur MMC” CJSC is considered, in which the extended rock masses affect the stress-strain state of the inter-wall rock mass. The problem is solved by using the constructed 3D physical modeling stand consists of lower immobile and upper moveable prisms. By considering the open-pit wall and the non-exposed mountain rock mass as one geomechanical environment, assessing the critical slip surface by using the well-known stability analysis software, the maximum height of the mountain slope is determined. It is shown that the natural mountain slope, extending above the last bench of the open-pit wall does not impact on the stress-strain field, and hence the stability, of the inter-wall rock mass of its overall height.

Technical and technological solutions regarding the development of pillars during final mining of deep open pits

When mining operations achieve the total depth of open pits within their boundaries, a significant share of balance ore reserves remains in pillars under transport communications as well as under reloading points. Liquidation of the available transport communications should follow by the development of the new ones. Hence, mining stages of a steep-grade field and periodicity of a pillar initiation within both working open pit flank and temporarily nonworking one have been studied. Нannivskyi open pit has been taken as an example to substantiate the expediency to extract balance reserves occurring under crushing and reloading point within ±0 m level. The substantiation of technical and technological solutions concerning the development of a protective pillar involved cuts of geological ore formation which supported the idea of availability of the preserved reserves and topicality of the selected problem. Operation schedules to mine the pillars have been developed for general conditions; the required equipment set has been analyzed. New technological solutions have been obtained using current excavating and transportation machinery. Engineering solutions as for possibility to open the pillars and liquidate them in terms of the limited technical and technological potential have been substantiated. The technological schemes of pillar mining have been systematized depending upon the technological processes, taking place in the open pit, and the applied equipment set. Scientific significance of the paper is the developed systematization of facilities in terms of operation schedules of pillar mining. Practical significance is the developed operation schedules to mine and liquidate the pillars. Technical and technological expediency to use skip hoist while reactivating temporarily nonworking open-pit walls for rock mass transportation from the pillars up to the surface has been substantiated. It has been proved that during final mining operations in an open pit, complicated by difficulties in electricity delivering to the preservation pillar, it is expedient to apply loaders in one operation schedule. Use of loaders and skip hoist to mine the preservation pillar is the optimum strategy. It has been substantiated that the proposed procedure is more advantageous to compare with the conveyor transport.

Features of using equipment for in-pit crushing and conveying technology on the open pit walls with complex structure

Purpose is to substantiate the use of an in-pit crushing and conveying technology at the open pits with complex structure of the working zone, which technological complex includes inclined and steeply inclined conveyors for improved economic efficiency of mineral mining at deep levels. Methods. The study applies a complex method including: technical-economical analysis of the practice of mining enterprises, experience of using conveying units at concentration plants and open pits; mining-geometrical analysis in terms of open pit sections – to identify the structure of the working zone of a deep open pit wall and its features along the depth; structural developments – to improve the design of a steeply-inclined conveyor; simulation modelling of the technological processes – to select optimal technical solutions. Findings. Basing on the performed studies, it has been identified that transfer to a new trend of the in-pit crushing and conveying technology, considering the structural features of the working zone of a deep open pit, is rather prospective. In this context, it is expedient to use inclined conveyors or deep-trough conveyors on the sites of an open pit wall with the inclination angle of 10-18°; in case of sites with the inclination angle of 30-36°, it is recommended to use steeply inclined conveyors. Originality. For the first time, a relation between the working zone of a deep open pit and formation of the structure of technological complexes has been identified. Dependences of the boundary inclination angle αn of a pipe conveyor on the angle of non-filling θ of its belt with the cargo at different coefficients of cargo-belt friction have been defined. Practical implications. The obtained results make it possible to widen the application sphere and increase the efficiency of mineral mining with the use of in-pit crushing and conveying technology.

Probabilistic assessment of slope stability at ore mining with steep layers in deep open pits

Purpose. A methodology development for predicting the geomechanical situation when mining an ore deposit with steep-dipping layers, taking into account the uncertainty in determining the rock properties, which is a consequence of the rock mass heterogeneity. Methods. The assessment of the open-pit wall stability is based on a combination of numerical simulation of the rock stress-strain state (SSS) and probabilistic analysis. The finite element method is used to determine the changes in the SSS that occur at various stages of mining operations due to design changes in the overall open-pit slope angle. The elastic-plastic model of the medium and the Mohr-Coulomb failure criterion are implemented in the codes of the 3D finite element analysis program RS3 (Rocscience). Stochastic simulation is used to assess random risks associated with natural object state variations. Findings. The distribution of maximum shear strains, which localizes the real or potential sliding surfaces in the open-pit wall at various stages of ore mining, has been identified. Based on the Shear Strength Reduction procedure, the open-pit wall Strength Reduction Factor (SRF) has been determined. The probabilities of open-pit wall stability loss, as well as the decrease in the strength reduction factor below the standard level at all stages of the ore body mining, have been revealed. Originality. For the first time, for real mining-geological conditions of a deep ore open pit, the dependence of the strength reduction factor on the overall wall slope angle, which changes during mining of each steep layer, has been determined. For each stage of mining operations, for the first time, the probability of a decrease in the open-pit wall stability below the standard level has been determined based on stochastic simulation. Practical implications. The ratio between the open-pit contour characteristic (overall slope angle) and the probabilistic safety factor is the basis for practical solutions to ensure the efficiency and safety of mining at various stages of friable and hard overburden excavation, ore extraction, as well as for the subsequent optimization of the open-pit design contours.

Substantiating the rock mass control parameters based on the geomechanical model of the Severny Katpar deposit, Kazakhstan

Purpose. The research purpose is to develop a geomechanical model for ensuring the safety of mining operations by determining the optimal slope angles and probabilistic assessment of the stability of the open-pit walls. Methods. Three-dimensional geomechanical models for surface mining of deposits have been developed based on calculations of the stability factor (safety factor SF) of the open-pit walls in the Rocscience program to determine the rock mass stress-strain state at the end of mining using the finite element method. The geological wireframe model (GWM) has been built on the basis of the available geological sections, horizon plans and the results of the engineering-geological surveys using the Surpac geoinformation system. Findings. Strength reduction factor (SRF) has been determined taking into account the physical-mechanical properties of rocks that constitute the near-wall mass. An assessment of the stability of walls according to the selected geological sections is given, taking into account the projected contour of the Severny Katpar open-pit walls. The calculation of the projected contour stability of the open-pit walls by several different methods has revealed that the open-pit walls are generally stable. The open-pit parameters at the end of mining have been determined. Originality. For the first time, it has been determined that in the Southern and South-Western area of the Severny Katpar open-pit wall in the horizons +700…+400, there is a decrease in SF from 1.18 to 1.41 due to the predominant occurrence of siltstones and tectonic disturbances of the walls. Practical implications. The mathematical calculation results of the stability of the projected contour walls in the Severny Katpar open pit have been generalized. In addition, a geological and structural wire-frame model of the deposit has been developed, which makes it possible to ensure the safety of mining operations in the open pit.

Rock mass management to ensure safe deposit development based on comprehensive research within the framework of the geomechanical model development

Purpose. To create and study a three-dimensional geomechanical model in order to determine the parameters of the open-pit walls and benches, ensuring safe and economically feasible mining, as well as predicting unstable zones within the open pit. Methods. A comprehensive methodological approach is used, including a systematic analysis of scientific, normative and methodological literature; analyzing the results of previously performed studies on the object; engineering-geological surveys in the near-edge rock mass of the Kurzhunkul’ deposit; laboratory testing of rock strength properties; determining the rock mass rating according to the MRMR classification; kinematic analysis of bench faces; calculating the stability of the Kurzhunkul’ deposit final boundary using the limit equilibrium method; numerical modeling of the rock mass stress-strain state at the Kurzhunkul’ deposit using the finite element method. Findings. The paper represents the results of data collection and analysis for the development of a geomechanical model of an operating iron-ore open pit in the Republic of Kazakhstan. Comprehensive geomechanical studies to substantiate the optimal parameters of the Kurzhunkul’ deposit walls and benches on the limiting contour, as well as calculations to determine the degree of the open-pit walls and benches stability have been performed. Based on the results of studying the geological-structural configuration of the deposit, as well the mathematical modeling data of stability and acting stresses, subsequently entered into a unified digital database, weakened zones have been identified. Originality. For the first time, the geomechanical model has been created for the conditions of the Kurzhunkul’ deposit, which makes it possible to combine in one database all the parameters that affect the safety of mining operations. The model takes into account structural disturbances of the rock mass that have an adverse impact on stability. Practical implications. The developed model gives a visual representation of the rock mass state at various sites of the deposit, simplifies the selection of design sections for stability calculations, facilitates the choice of optimal technical solutions and analysis, especially for complex geological structures with multiple geotechnical or geological units with different texturing and inclination.

Assessing the capacity of dredging excavations to place dredging tailings dumps in the course of deep and man-made placer mining

Introduction. The dredge stern is often backed up by dredging tailings in the course of deep and man-made placers dredging. One of the reasons for that is the decreased capacity of dredging excavations at the dumping point caused by collapsed pit walls, which is not taken into account by known design methods. Research objective is to evaluate the degree of the developed space capacity reduction at dredging pits for dredging tailings storage, depending on the dredging conditions. Methods of research. Capacity prediction for a dredging excavation for dredging tailings storage should consider natural slope formation of open pit walls during the period of dredge advance to a distance equal to the distance of the poop decks from the face. The degree of reduction in dredging excavation lower part receiving capacity should be set based on pit walls flattening, which depends on rock composition (cohesiveness degree), loose deposits thickness, face width, and dredge working parameters. Results. The results of graphic-analytical calculation revealed that dredging excavation lower part receiving capacity is reduced from 3 to 10% due to pit walls collapse as loose deposits thickness increases from 10 to 34 m for the most favorable face width of a 380-liter dredge, which may result in a significant increase in dredge stern backing up by dredging tailings. Conclusions. At deep and man-made placers, when calculating the parameters of a dredging tailings dump, it is recommended to introduce an amendment into the existing methods, that considers the developed space lower part capacity reduction due to pit walls collapse.

Задачи развития перспективных циклично-поточных технологий для глубоких карьеров

The development of open pits, both in terms of their mining intensity and a significant increase in the current and design depth, requires improvement of transport systems that form the bulk of the production cost. One of the most proven types of combined transport that provides high productivity is the truck-and-conveyor system. Therefore, this paper focuses on its adaptation to the future mining conditions (high dynamics of open pit mining development with creation of deep quarries, the need to reach open pit depths of up to 800–1200 m). The field of application of different types of transport is not static and changes along with the technical development of transport means, their introduction into mass production, and a change in the target group of mining and operating conditions. The article provides a systematization of open-pit transport applicable in modern conditions and shows the experience gained by the Institute of Mining of Ural branch of RAS in the in-pit crushing and conveying technology, mobile (semi-stationary) crushing and reloading plants and self-propelled crushing units. The results of calculations and technical and economic parameters of open-pit truck haulage and conveyor transport in a wide range of mining conditions are described. It is shown that an urgent research and engineering challenge is the development of technologies for the phased introduction of high-performance equipment for in-pit crushing and conveying transport to a great depth with a minimal additional extension of the open pit walls. At the same time, it is possible to use both steeply inclined and traditional belt conveyors, depending on the specific operating conditions. Conveyor transport is preferable for use at the main stage of the life cycle of deep quarries in terms of its efficiency and throughput, but its use is constrained by a number of factors considered in the paper.

DEVELOPING A 3D PHYSICAL MODELING STAND TO RECORD STRESSES IN NATURAL-MOUNTAIN-LOADED OPIN-PIT WALL

A 3D physical modeling stand has been developed to study the redistributed stress field and pattern consistency of the stresses in the exposed open-pit wall on the mountain terrain due to natural unexposed slope of the mountain above the crest of the wall under loading conditions. In such a geotechnical analysis, the modeling stand can also be used to determine the rational parameters of the multistage waste rock dumps or stockpile structures constructed on shallow terrain, as well as in hard topographical conditions, based on the assessments of the redistributed stress field due to each depositing layers. The above-mentioned 3D physical modeling stand to define the stresses in natural-mountain-loaded open-pit wall have been certified as a patent by RA Intellectual Property Agency of N 713 Y.

Волоконно-оптический длиннобазовый деформометр для системы мониторинга горных пород бортов карьеров

A fiber-optic long-base deformometer has been developed, which can be used in rock monitoring systems for open pit walls. The proposed deformometer is based on the method of controlling the additional losses of a light wave propagating in an optical fiber. The fiber optic sensor has a fairly high linearity and stability of the output signal, and is also not subject to the negative occurrence of fading inherent in fiber optic sensors based on the Mach-Zehnder interferometer, with fluctuations in ambient temperature and the appearance of false signals about the displacement of rocks.

Fiber Optic Long Baseline Deformometer for Pit Wall Rock Monitoring System

A fiber-optic long-base deformometer has been developed, which can be used in rock monitoring systems for open pit walls. The proposed deformometer is based on the method of controlling the additional losses of a light wave propagating in an optical fiber. The fiber optic sensor has a fairly high linearity and stability of the output signal, and is also not subject to the negative occurrence of fading inherent in fiber optic sensors based on the Mach-Zehnder interferometer, with fluctuations in ambient temperature and the appearance of false signals about the displacement of rocks. Keywords: deformometer, interferometer, monitoring system, optical fiber.

Stress-strain state and stability of the Unglichikan open pit walls

Research objective is to identify the features of stress-strained state development and estimate the stability of Unglichikan open pit walls and dump slopes based on calculation, analysis, and estimation with the certified finite element method GenIDE32. The introduction describes features of research object location natural-technogenic conditions and geological history of rocks building up the research object. Research relevance is due to complex solution to deep and high mountain structures design problems, account for construction technologies, and stress-strained state and elements stability determination. Methods of the stress-strained state numerical calculation, analysis, and estimation for the “structure– geological environment” system consists in using all tools of the program’s interface, namely, values, value levels, isolines and graphs for different quantities, including the graphs of stress-strained state behavior trajectories in the space of the stress tensor invariants and relative strains. Results of calculation are presented as the program’s capabilities in graphic representation of the sequential development of mudslides in open pit walls and dump slopes with vertical fissures. Colors of magnitude levels specify the contours of mudslides, while the corresponding shading of finite elements indicates the fissure formation sites. Conclusions. Calculation results proved the stability of the mountain structures for the selected size dimensions of open pit walls and dump slopes.

Geomechanical substantiation of the Oleniy Ruchey deposit underground mining in a protective pillar of the Niorkpakhk open pit

The location of significant volumes of the lower level reserves close to an open pit which produces the adjacent Niorkpakhk deposit considerably complicates underground mining of the Oleniy Ruchey rockburst-hazardous deposit. The progress of underground excavations into the under-pit space is permitted if the undermined rock thickness and open pit walls remain stable. 3D numerical studies of stress-strain state have indicated particularities in deformation such as increase in undermined thickness stability under high tectonic stresses. The parameters of safe mining of temporary inactive reserves were scientifically substantiated. The boundaries of maximal development of underground mining were determined. The stability of overlying rocks and open pit walls is maintained by forming an advance of overlying sublevels relative underlying ones under 45° angle and providing the monitoring for the undermined rock mass. The mining method in a protective pillar the authors propose allows increasing reserves of the first mining stage by 76.9% and avoiding decrease in production volumes when mining operations terminate.

Determination of bench, dump and road sliding wedge technological parameters

Mine surveying in mining operations is of particular importance, since all technological processes of the full life cycle of a mining enterprise and, ultimately, its competitiveness depend on the surveying quality, efficiency and reliability. Organizations independently determine the structure of mine surveying services, taking into account the methods applied and the scale of mining. To ensure safe open-pit mining of minerals, it is necessary to permanently assess and monitor the pit bench and wall rock mass condition. Misjudgement of rock physical and mechanical properties, non-observance of the minerals mining and transportation process cycle, changes in climatic conditions and other problems lead to loss of stability of rocks in all parts of an open pit, including in the areas of ore production and mining and transport equipment operation. The existing practice shows that the effectiveness of an open pit wall and bench stability calculation can be achieved using a technique that should take into account the slope deformation and failure mechanism, as well as the nature of the stress-strain state of the open pit rock mass. The studies presented in the paper are based on comparative analysis of the sliding wedge parameters for benches, dumps and roads at open pits using analytical and graphical software packages, and taking into account the static load produced by dump trucks. The study findings allow to establish that: determination of the bench slope stability and the sliding wedge width, performed by the analytical method, gives higher accuracy results than those obtained by the graphical method; the bench slope stability and the sliding wedge width depend not only on the rock physical and mechanical condition, but also on the bench height, the dump truck (plus its freight load) weight per 1 linear meter of the placement area, the distance from the slope edge and other factors; the rock mass is stable and not subject to landslide phenomena for as long as the sum of the holding forces is greater than or equal to the sum of the shearing forces; when using large-sized transport equipment of nonstandard weight in open-pit mining, it is necessary to calculate the safe width of the sliding wedges, taking into account the loads on them (per 1 linear meter), the values of which can be 1.5–2.0 times higher than those calculated for the circular-cylindrical sliding surface.