Pit Walls Research Articles

Design acceptance criteria for operating open-pit slopes: An update

ABSTRACT Open-pit slope engineering involves balancing economic imperatives and risk, where an optimum pit slope design seeks to safely steepen the pit slope angles to minimize the mining of waste, therefore maximizing ore recovery. Open-pit Design Acceptance Criteria (DAC) had been proposed and adopted by industry, and the Guidelines for Open Pit Slope Design, published in 2009, finally provided a consistent set of guidelines. Since the publication of these guidelines, it has been the industry experience that practical DAC requires consideration of multiple levels of design confidence, ranging from highly uncertain greenfield sites to mature operations; the unique nature of consequences associated with open pit wall failures as opposed to other civil and mining structures; and differences between operators’ risk appetite. This article presents the state of practice for inter-ramp and overall open-pit slope design in the mining industry and develops flexible DAC for operating pits that addresses the considerations outlined. The criteria are rooted in robust risk tolerance principles, previously adopted criteria, a database of open-pit designs, and mathematical validation for criteria in terms of both Factor of Safety (FoS) and Probability of Failure (PoF).

ОЦЕНКА ГОРНО-ГЕОЛОГИЧЕСКИХ И ГОРНОТЕХНИЧЕСКИХ УСЛОВИЙ КАРЬЕРА «СЕВЕРНЫЙ» С ПОМОЩЬЮ МАТЕМАТИЧЕСКИХ МОДЕЛЕЙ

One of the most important indicators characterizing the operating conditions of the fields is the water cut. It negatively affects the way of mining and the possibility of effective use of modern mining technologies. The high water cut of the cover and ore-hosting rocks often serves as the main reason for a decrease in their stability and the manifestation of negative processes (quicksand properties of rocks, caving), as a result of which the safety of miners deteriorates and high-performance mining methods become inapplicable, which generally leads to a decrease in the technical and economic indicators of the open pit. Thus, the study of the regularities of the formation of water inflows in the “Severny” open pit, based on the use of factual material and the development of a sound forecasting methodology are relevant. Purpose of the study. Analyze and assess the mininggeological and mining-technical conditions of the open pit “Severny” using mathematical models. Research methodology. The work uses a modeling method to predict water inflow and calculate the drainage of a quarry field in difficult mining conditions. Devices simulating natural mining conditions were used: a device for electrohydrodynamic analogies (EGDA). Research results: An analogy has been drawn between the phenomenon of laminar steady-state filtration of water in rocks and the passage of current in an electrically conductive medium in the form of electrically conductive paper, less often in liquid electrolytes. The EGDA device was used to determine the water inflows into the quarry, taking into account the factors that complicate the calculations of groundwater filtration (for example, taking into account the movement of the walls of the quarry, the operation of drainage devices, the infiltration of atmospheric precipitation, the movement of water in neighboring aquifers of different permeability), modeling of objects with a complex configuration boundary contours. Conclusion. The modeling method has been improved, which makes it possible to substantiate the use of a specific mining method under certain hydrogeological conditions and to select the optimal drainage scheme to increase the operational reliability of the open pit. The conducted research, observation, study of the existing dam showed the technical feasibility of further development of the deposit with minimization of financial costs. In order to ensure the safety of mining operations, it is envisaged to conduct constant and systemic mining and technical monitoring of mining operations and study the state of the water protection dam and pit walls.

Studying ore field structure and rock properties of the Delken deposit to substantiate the optimal pit walls design

Introduction. In order to determine a key design parameter substantiated by technical-economic and geomechanical analyses, the critical angle of slope of the nonmining wall in Delken deposit pit which depends on the properties and the state of rock building up the wall and its structures, and in order to determine the forms and the elements of mineral occurrence, the authors carried out comprehensive research consisting of the of deposit’s geological and structural features determination, including endogeneous and exogeneous jointing, and the detailed examination of physical and mechanical properties of rock and ore. Research aim is to study geological-structural properties of the deposit in order to analyze and substantiate the optimal and safe structure of pit walls when developing ore at the Delken gold deposit. Methodology. The structural features of Vodorazdelny ground were determined by carrying out the comparative analysis of geological sections and maps, structural description of core and building the scheme of rock blocking according to the level of destruction during deposit opencast. Physical and mechanical properties of rock were determined in laboratory conditions. Numerical analysis of wall stability was fulfilled with modern software. Results. The comprehensive research consisting of the analysis of mining and geological conditions of development, deposit’s geological and structural features determination, detailed examination of the properties of rock building up the slopes of the quarry have made it possible to substantiate the rational design of pit walls when developing ore reserves of the deposit. Summary. The results of the research carried out at the deposit may be applied when substantiating the safest technology of uncovering the deposit and the safest mining sequence.

Taking into account dynamic influences on geotechnical structures in conditions of compaced urban buildings on the example of Kyiv

The applied technique of taking into account the dynamic effects on geotechnical structures in the conditions of compacted urban development with direct dynamic calculations taking into account the experimentally obtained accelerograms has been further developed. The methodology includes: visual and vibrodynamic inspection of the new building of the geotechnical structure and existing sources of vibrodynamic influences (taking into account the natural seismic background – seismic zoning of the construction site); construction of a calculation model; performing direct dynamic calculations of anti-landslide structures (pit walls, stress-strain state of the surrounding construction site soil, superstructure, etc.) taking into account the actual experimentally obtained accelerograms for the studied geotechnical structure (superstructure, etc.); analysis of compliance of the received settlement and design data of the new building with the current normative documents on seismic construction; if necessary – issuance of recommendations for strengthening the relevant building structures of the foundation and (or) superstructure. Determination of dynamic characteristics of soil and building structures is based on their free oscillations of small amplitude, which are disturbed by natural or man-made microseismics, includes: registration of oscillations using highly sensitive (in our case – seismic) sensors; calculation and analysis of Fourier spectra in order to isolate resonant peaks corresponding to different forms of free oscillations; obtaining by means of the inverse Fourier transform of pulsed realizations of the selected resonant peaks on each form of free oscillations of designs; identification and graphical representation of various forms of oscillations of the studied soil, geotechnical structures, etc. An example of vibrodynamic studies of the soil and individual building structures of the buildings of the Post Square to determine the actual dynamic loads on the soil and protective walls of the pit of the construction site is considered.

Sediment infilling and geomorphological change of a mud-capped Raccoon Island dredge pit near Ship Shoal of Louisiana shelf

To restore degraded barrier shorelines of the Mississippi River Delta of coastal Louisiana, sand is dredged from high-quality borrow areas on the adjacent continental shelf. This dredging process generally creates a topographic low that facilitates the rapid capture of sediments. Our understanding of sedimentary processes and influences on seabed morphologic evolution is still limited. In this study, Raccoon Island dredge pit in a paleo-river channel on the Louisiana shelf was studied via multiple bathymetric surveys. Physical parameters include pit geometry and topographic change from post-dredging, and infilling sediment sources were analyzed. Raccoon Island pit was 100% filled up less than six years after dredging. The average infilling rate in the Raccoon Island pit was 1.10 m/year from 2013 to 2018. During the surveying period, the pit wall slope decreased by 6.8° within two years. The sediment infilling process in the Raccoon Island pit was likely under the combined influence of topography, wind-driven currents, storm waves, and the dynamic Atchafalaya River dispersal system. The Atchafalaya River reached high discharge in 2016, which likely contributed to a surprisingly high sediment infilling rate at Raccoon Island pit between 2015 and 2018. Raccoon Island pit is in a mixed texture environment in which the sandy pit was fully filled with mud. Mud is useful for marsh restoration but is not considered a quality resource for barrier island or beach restoration. Thus, the Raccoon Island pit is not regarded as a renewable resource for future barrier island restoration.

Continuous Monitoring and Improvement of the Blasting Process in Open Pit Mines Using Unmanned Aerial Vehicle Techniques

The current techniques used for monitoring the blasting process in open pit mines are manual, intermittent and inefficient and can expose technical manpower to hazardous conditions. This study presents the application of unmanned aerial vehicle (UAV) systems for monitoring and improving the blasting process in open pit mines. Field experiments were conducted in different open pit mines to assess rock fragmentation, blast-induced damage on final pit walls, blast dynamics and the accuracy of blastholes including production and pre-split holes. The UAV-based monitoring was done in three different stages, including pre-blasting, blasting and post-blasting. In the pre-blasting stage, pit walls were mapped to collect structural data to predict in situ block size distribution and to develop as-built pit wall digital elevation models (DEM) to assess blast-induced damage. This was followed by mapping the production blasthole patterns implemented in the mine to investigate drillhole alignment. To monitor the blasting process, a high-speed camera was mounted on the UAV to investigate blast initiation, sequencing, misfired holes and stemming ejection. In the post-blast stage, the blasted rock pile (muck pile) was monitored to estimate fragmentation and assess muck pile configuration, heave and throw. The collected aerial data provide detailed information and high spatial and temporal resolution on the quality of the blasting process and significant opportunities for process improvement. The current challenges with regards to the application of UAVs for blasting process monitoring are discussed, and recommendations for obtaining the most value out of an UAV application are provided.

Averaging the operating stripping ratio for sinking mining systems based on mathematical simulation

The article contains the research results for a rational mining mode, definitions, and averaging of the operating stripping ratio. When determining the mining mode using open-pit hydraulic excavators, the problem appears with averaging the operating stripping ratio. Averaging is usually achieved by changing the pit wall angle at the expense of the respective change in the bench width. Minimum bench width serves as a limiting factor if working benches have to be reduced during the open pit mining. Continuous mining operations in an open pit require calculation and averaging the operational stripping ratio. There is a classical approach to calculate the average operational stripping ratio, but this method is graphical and has some errors. Therefore, a mathematical simulation was carried out based on integral calculus to obtain more precise values.

USE OF LASER SCANNING TECHNOLOGIES FOR OBSERVATIONS OF DEFORMATIONS OF OPEN PIT WALLS

The article discusses the use of laser scanning technology for observing the deformations of an open pit walls in iron ore deposits. To carry out observations and analysis of the results obtained, an iron ore quarry was selected. The task of the study is to summarize methods and technical means used at mining enterprises for observing and measuring deformations in mountain ranges. The safety and efficiency of iron ore quarries is largely determined by the methods used to monitor the deformation process and calculate the stability of the pit walls and dumps. Based on the analysis of existing approaches to solving this problem, a conclusion was drawn on the advisability of using a laser scanning system for assessing sustainability. As a result, an analysis of the measurement results obtained in a digital model of the quarry near-surface arrays was obtained, which allows creating an electronic database for further use in surveying and geomechanical tasks.

Corrosion of initial pits on abandoned X52 pipeline steel in a simulated soil solution containing sulfate-reducing bacteria

In this work, corrosion of an abandoned X52 pipeline steel containing artificial pits with varied depths was investigated in a simulated soil solution containing sulfate-reducing bacteria (SRB). Bio-testing, electrochemical measurements and surface analysis techniques were used to study the SRB-induced corrosion outside and inside the pits. Results show that the SRB tend to accumulate on the specimen surface (i.e., outside the pits), rather than inside the pits, resulting in accelerated corrosion of the steel. As the depth of the pit increases, there are fewer SRB adherent to the steel of the pit wall. Thus, compared to the specimen surface, the pits experience a reduced MIC. A galvanic effect exists between the outside and inside the pits, with the former serving as the anode and the latter as the cathode, further enhancing the corrosion of the steel outside the pits.

Geomechanical justification of geotechnical situation in coal extraction with highwall mining system

One of the most effective approaches to reduction of coal loss in open pit within ultimate limits is extraction of coal reserves from the pit walls and bottom using the highwall mining systems. The high efficiency of the method is conditioned by minimal capital cost and reuse of the existing geotechnical infrastructure. On the other hand, the safe application of this approach depends on the rock mass quality. In mining practice, the major application area of the highwall mining systems is pitwall rock mass of damping jointing. In this connection, this paper aims to estimate influence of rock mass quality on stability of pit wall and underground openings (rooms and pillars). The set problem is solved by the finite element modeling of geomechanical situation for standard conditions of an open pit coal mine. The novelty of the research consists in more comprehensive inclusion of rock mass lithology, jointing, deformation and strength characteristics, initial stress state and structural features of technology in the problem solution.

Identification of displacement zone in extraction of coal reserves from pit wall by highwall mining systems in the Talda deposit in Kuzbass

Identification of displacement zone in extraction of coal reserves from pit wall by highwall mining systems in the Talda deposit in Kuzbass

Geomechanical monitoring of ground surface and pit wall deformations

Geomechanical monitoring of ground surface and pit wall deformations

The Challenges of Open-Pit Mining in the Vicinity of the Salt Dome (Bełchatów Lignite Deposit, Poland)

The extraction of the Bełchatów lignite deposit located in the vicinity of the Dębina salt dome requires careful planning that considers the influence of mining projects on the slope and salt dome stability conditions. The instability problem is directly related to horizontal and vertical displacement, as well as the complex geological and mining conditions. These conditions are very unique with regard to the co-occurrence of the salt dome and lignite deposits in the same area, as well as the large scale of the pit wall slope. Thus, predicting rock mass behavior and ensuring the safety of mining operations are important issues. The presented analysis focused on the influence of long-term lignite extraction on the western pit wall slope of the Bełchatów field and the salt dome’s stability conditions. This study offers a comprehensive approach to a complex geotechnical problem defined by large-scale, complex geometry, and geological conditions. The rock mass behavior and stress conditions are simulated in numerical modelling. The results of the presented analysis will be useful not only for present mining activities but also for future developments related to post-mining and recultivation plans.

Slope Stability in Open Pit Mines in Clayey Rock Mass

Justification of slope parameters for benches and pit walls in clayey rock mass bases on studies into geological structure and physical and mechanical properties of rocks of various lithological varieties. The upper layers of pit walls occur in weak clayey overburden, in the crust of weathering and in transition zone with conglomerates, up to 150 m in total thickness. In this case, it is required to calculate accurately angles of clayey slopes, to undertake cutback at recommended angles and to eliminate heavy flow of melt water and rain water from ground surface to the slopes. Mining within the design pit wall limits should be accompanied by continuous instrumental monitoring of pit wall slopes.

ОЦЕНКА ВАРИАНТОВ ОТРАБОТКИ ПРИБОРТОВЫХ И ПОДКАРЬЕРНЫХ ЗАПАСОВ РУДНИКА «ОЛЕНИЙ РУЧЕЙ»

Актуальность исследования обусловлена необходимостью отработки новых рудных тел, появившихся в ходе проведения опережающей эксплуатационной разведки. За проектными контурами рудников остаются запасы, которые необходимо доработать либо подземным, либо комбинированным способами. При технологии доработки прикарьерных запасов возникают наибольшие сложности, поскольку их отработка вызывает нарушение обеспечения устойчивости откосов борта карьера. Поэтому поиск, выбор и определение главных параметров системы разработки прикарьерных запасов при доработке месторождений, обеспечивающих эффективное и безопасное освоение запасов, представляет весьма актуальную задачу. Цель: рассмотреть возможные варианты отработки прибортовых и подкарьерных запасов с учетом залегания новых рудных тел апатит-нефелинового месторождения и соблюдением необходимых условий для заданного направления развития горных работ в границах горного отвода и произвести технико-экономическую оценку предложенных вариантов. Объект: крупное месторождение апатит нефелиновых руд «Олений ручей». Методы: горно-геологический анализ верхнего яруса месторождения апатит-нефелиновых руд «Олений ручей» и анализ существующих данных о физико-механических свойствах горных пород, слагающих массив рассматриваемого месторождения, анализ возможных схем развития горных работ при отработке прикарьерных запасов с оценкой возможности внутреннего отвалообразования при доработке карьера. На примере разработки месторождения апатит-нефелиновых руд «Олений ручей» авторами рассмотрены возможные варианты отработки и вскрытия прибортовых и подкарьерных запасов верхнего яруса месторождения с соблюдением условий развития горных работ в границах горного отвода. Предложено оптимальное развитие горных работ по варианту, предусматривающему минимальный коэффициент вскрыши.

Degassing Pit Lakes: Technical Issues and Lessons Learnt from the HERCO2 Project in the Guadiana Open Pit (Herrerías Mine, SW Spain)

The unique case of carbon dioxide accumulation in the bottom layer of the acidic lake formed in the Guadiana open pit (Herrerias mine, SW Spain) led to exceptionally high dissolved gas pressures (ca. 5.0 bar at depths of 50–70 m). This CO2 has formed by carbonate (calcite, dolomite) dissolution during decades of interaction of the acidic water with the rocks of the pit walls and associated mine tunnels. The elevated dissolved gas pressures were only comparable to those found in the volcanic crater lakes of Cameroon like Nyos and Monoun, which erupted in the 1980s and sadly triggered the loss of hundreds of human lives. This gas pressure was not far from the absolute (hydrostatic plus atmospheric) pressure limiting CO2 solubility at depth, thus making this pit lake potentially dangerous for the possibility of a hypothetical limnic eruption. Following detailed field and experimental studies aimed at deciphering the source and accumulation patterns of CO2 in the lake, a degassing project started in 2014, which followed an upscaling strategy with construction and installation of progressively bigger pipelines capable of extracting increasingly higher flow rates of CO2-charged water from the deep part of the lake. As of May 2019, the degassing systems have successfully extracted most of the CO2 originally present in the lake (i.e. ≈ 123,000 m3 CO2), which has been discharged to the atmosphere in a controlled and safe way. The fountains became progressively smaller and finally stopped, due to the decreased gas pressure at depth. The larger pipes will serve as a regulating system in the future. This paper describes the main findings encountered during the degassing project, some relevant technical issues observed during the last 5 years (2014–2019), and lessons learnt from the Guadiana pit lake experience.

Morphological evolution of a mud-capped dredge pit on the Louisiana shelf: Nonlinear infilling and continuing consolidation

Buried sandy paleo-river channels on the continental shelf can be accessed through dredging for the restoration of beaches and barrier islands which are under the threat of land loss and rising sea levels. However, our knowledge on post-dredging evolution of paleo-river channels is still very limited. In this study we focus on infilling rate, sediment acoustic characteristics, slope change and surficial morphology, all of which have implications for the management of seafloor oil and gas infrastructure. Bathymetric data collected during nine bathymetric surveys over 13 years were used to study the long-term changes of the Peveto Channel dredge pit, which is ~5 km offshore of Holly Beach in western Louisiana, USA. This pit was constructed in 2003 and was completely infilled in or before 2016. Initial pit infilling rates began at 214 cm/year from 2003 to 2004 and then rapidly decreased to an average rate of only 33 cm/year from 2006 to 2016. This corresponds volumetrically to 418,753 and 80,816 m3/year for the same intervals. Pit wall margins displayed small lateral migration, moving <30 m outwards over 13 years, posing minimal threat to adjacent infrastructure. After complete infilling, numerous small mounds were found on 2016 bathymetry, morphologically resembling ‘mud volcanoes’ that have been reported on deltas, continental shelves and slopes around the world. Newly deposited sediment on seafloor surface had a reflectivity lower than the ambient seafloor environment. Massive amounts of sediments were transported to the pit despite no proximity to direct riverine inputs, making the pit act as an efficient sediment trap. Inferred depth-integrated lateral sediment transport rates were 9.91–12.73 g/m/s. Despite the fact that Peveto Channel pit was filled up, consolidation continues and the filled sediment surface hasn't reach a condition in equilibrium with ambient seafloor yet. Our results highlight the continuing dewatering and long consolidation processes at the pit site even after a complete infilling.

Interpreting displacement data from complementary slope monitoring systems in extreme weather conditions

ABSTRACT As costs decrease for displacement monitoring radar units, open-pit operations increasingly incorporate multiple monitoring systems to track displacement of pit walls. At the Teck Resources Ltd. steelmaking coal operations in British Columbia and Alberta, Canada, a common practice is to couple a radar system with the installation of survey prisms. The two systems work in different ways and provide more continuous monitoring of displacement when one system is adversely affected by the punishing weather conditions at the mining operations. While there are circumstances when results from one system can be discounted, there are often instances when results from either system cannot be ignored even though they are suspect. This paper presents a methodology to evaluate results in such circumstances. It links the monitoring system status, pit-wall displacement trends, perceived risk, and recommended course of action in a manner that addresses the uncertainty of results from one or both systems.

The integrated geodetic monit oring system of open pit slopes in hard rock massifs

The article describes an experience in organizing the integrated geomechanical monitoring in high-strength hard rock massifs using the longstanding GPS and optical distance measurements in the Zhelezny open pit, Kovdorsky GOK JSC, as well as measurements with the IBIS FM interferometric radar. The application of the integrated monitoring system in the Zhelezny open pit has allowed accumulation of significant statistical material, which made it possible to identify the patterns of the rock mass deformation development, determine the limiting parameters and develop several regulatory documents for observing and processing the measurement results of the benches and open pit walls displacements.

Limitations on seismic effects of technological explosions in the combined development of the Sarbai deposit

The issue of joint production of drilling-and-blasting operations (DBO) is acute in the combined field workings with the condition of underground mining in the edge massif of the pit walls. Normally, the underground mine construction begins with the quarry depth approaching the end marks. In this situation, even if there is any volume for wall cutback, it is very insignificant and blasting works come closely to the limit circuit of the quarry, behind which the protected massif is located and underground workings is supposed to be carried out in the future. The main task in carrying out DBO under such conditions is to maintain the stability of this massif. Timely explosion shielding and the creation of contour fracture surfaces by applying controlled blasting reduce the negative explosion impact on the edge, yet do not always prevent the stress waves spread across the massif caused by seismic effect. Therefore, limiting the explosion seismic action in the border zone is as important for the massif stability as the professional pre-splitting.