Sublevel caving is a highly mechanizable mass mining method normally utilized in large, steeply dipping orebodies. The fragmented ore flows freely, aided by gravity, down to the drawpoint while the surrounding waste rock caves in due to induced stresses and gravity. Fragmentation of the blasted ore is a vital component in any mining operation and directly affects productivity and efficiency of the following production steps (Nielsen et. al, 1996). In an attempt to reduce mining induced seismicity in Malmberget, LKAB is initiating various trials. One of these trials involves a reduction in blasthole dimension and an increase in the number of blastholes utilized in each ring. A reduction in blasthole dimension is undertaken to achieve a less impactful mining operation in terms of disturbances to surface populated areas, particularly addressed to ground vibrations. Therefore, it is of utmost importance to analyse if fragmentation and production is affected as a consequence of this change. This thesis sets out to evaluate how fragmentation and the LHD operation is affected by variations in blasthole dimension. The evaluation is carried out through analysis of logged production data, on-site filming of the loading sequence and interviews with the LHD operators. The discoveries will be presented chronologically to illustrate the complexities related to compiling a viable dataset to rely on for a credible analysis. The initial theory did not hold up properly and therefore the project was reshaped along the course of progression to provide further information and clarify uncertainties. Unfortunate, major production delays inhibited a quantitative comparison of two parallel drifts with different blasthole dimensions. Hence, no final answer can be provided in this thesis whether a change in blasthole dimension causes any differences in loadability and/or fragmentation or not. However, an analysis of how cycle times vary depending on causes such as operator induced differences, machine induced differences and road conditions will be provided. The field test also provides information on various loading scenarios and the difficulties connected to these. The result obtained in this project mainly addresses the significant operator difference in terms of cycle times which can extend to, on average, 60% depending on experience, road conditions and, most likely, preferences amongst operators. Time differences amongst seemingly experienced operators can reach more than, on average, 30% in hauling time alone. Roughly 96% of the operators state that road conditions in the production area is the controlling factor for hauling speed. Many of the operators further states that the risk of injuries is directly related to road conditions and this is a likely cause to why cycle times vary in this magnitude. Fragmentation was found to affect loadability but not to the same extent as shape and looseness of the muck pile. Compaction of the muck pile and flow disturbances where normally found to be connected to one another. Hence, good loadability would indicate a low occurrence of flow disturbances and a continuous flow of material into the drawpoint. This thesis is written as a part of the final stage of the civil engineering program at Luleå University of Technology (LTU) and represents 30 credits in the field of Soil and Rock Construction. The thesis is a part of a larger project, Face to surface, which sets out to analyse the impact of fragmentation on different stages in the production chain.

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / This research study focuses on creating a drill pattern for the Condestable mine, which will allow us to assess the percentage of dilution. For these purposes, we used the Pearse formula proposed in 1955, which allowed us to find the burden and later, the spacing that each drill hole should have in the pattern. Once we had collected all the numerical data, we used the JK SimBlast program to design the proposed drill pattern and analyze the damage zones, the tonnage acquired and the existing dilution. According the results obtained, the smaller the hole diameter, the less dilution will be generated when diversifying the wall and ceiling explosives.

La investigación se plantea resolver el problema: ¿Cuál es el diseño de malla de perforación y voladura para estandarizar en el método de explotación Sublevel Caving en el tajo 6950 zona II Cuerpo Esperanza Mina Central Yauricocha 2018?, y como objetivo general: determinar el diseño de malla de perforación y voladura para estandarizar en el método de explotación Sublevel Caving; la hipótesis a contrastar consiste que el diseño de malla de perforación y voladura estandarizará en el método de explotación Sublevel Caving.

Comprehensive and reliable seismic analysis techniques can aid in achieving successful inference of rockmass behaviour in different stages of the caving process. This case study is based on field data from Telfer sublevel caving mine in Western Australia. A seismic monitoring database was collected during cave progression and breaking into an open pit 550 m above the first caving lift. Five seismic analyses were used for interpreting the seismic events. Interpretation of the seismic data identifies the main effects of the geological features on the rockmass behaviour and the cave evolution. Three spatial zones and four important time periods are defined through seismic data analysis. This thesis also investigates correlations between the seismic event rate, the rate of the seismogenic zone migration, mucking rate, Apparent Stress History, Cumulative Apparent Volume rate and cave behaviour, in order to determine failure mechanisms that control cave evolution at Telfer Gold mine.

Ingeniero Civil de Minas / La minería mediante caserones constituye el método de explotación subterráneo más empleado en Chile, en cuanto a número de faenas se refiere. De un catastro de 40 faenas nacionales subterráneas, un 55% de ellas utiliza caserones abiertos, un 13% corresponde a caserones con relleno y un 8% se explota mediante métodos por hundimiento. Actualmente, no se dispone de datos oficiales que permitan analizar las prácticas operacionales y de diseño de la mediana minería subterránea en Chile. Por esto, resulta necesario analizar y evaluar comparativamente las principales características e indicadores del método de explotación por subniveles, utilizado en éste tipo de faenas mineras, de manera de generar herramientas o procedimientos que permitan obtener mejores desempeños. Esta memoria forma parte del proyecto Innova Chile-Corfo 11IDL2-10630 denominado Desarrollo de Herramientas de diseño para minería subterránea selectiva en Chile y tiene como objetivo establecer el estado del arte de la mediana minería subterránea en Chile. El estudio se realiza mediante la elaboración de un catastro que reúne información de referencias públicas y la recopilada durante visitas y estadías en cinco operaciones subterráneas ubicadas en la zona centro y norte del país, las que utilizan caserones por subniveles como método de explotación. Los antecedentes recopilados incluyen: información general de la mina, geometría del yacimiento, mineralización, ritmos de producción, cantidad de personal, geología y geotecnia, costos, índices mineros, estabilidad de caserones y pilares, entre otras. La información recopilada ha sido procesada, tabulada y estandarizada de forma de ser comparable entre sí de manera agregada, con lo cual se obtienen los principales indicadores relacionados con el diseño, perforación, tronadura, carguío y transporte. Del estudio se desprende que el principal mineral en explotación es el cobre, encontrándose en el 80% de las minas visitadas. La calidad del macizo rocoso corresponde a un Rock Mass Rating (RMR) superior a 60, dando cuenta de una roca de buena calidad. Los índices de perforación varían entre 7,6-28 t/m para perforación Long Blast Hole (LBH) y entre 6-8 t/m para Undercut (UC). El factor de carga en tronadura LBH varía entre 220 y 300 g/t. Respecto a la base de datos de diseño y levantamiento topográfico, ha sido posible recopilar información de aproximadamente 100 caserones. Adicionalmente, en base a 51 mediciones de esfuerzos in-situ en faenas se propone una relación preliminar entre los esfuerzos vertical y horizontal con la profundidad. Se recomienda incorporar otras operaciones mineras en el estudio, con el objeto de realizar un compendio aún más distintivo del estado actual de la mediana minería de Chile. Los datos aportados por las empresas mineras deberán ser revisados en terreno para corroborar si son puestos en práctica y por ende determinar su representatividad. El análisis comparativo presentado en éste trabajo puede ser utilizado como una herramienta de consulta en el diseño de nuevos proyectos. La metodología de trabajo está orientada en el mejoramiento continuo de las prácticas operacionales y de diseño, estimulando cambios y mejoras en estos procesos.

[pt] O método de exploração Sublevel Caving é um dos métodos de extração massiva mais usados na indústria mundial de exploração subterrânea, sendo considerado pela indústria de mineração, num futuro próximo dentre os substitutos naturais das atuais minas a céu aberto. Uma operação Sublevel Caving requer que o maciço rochoso circundante ao minério rompa continuamente e se movimente para dentro do espaço criado pela extração do minério. Análises existentes na literatura consideram apenas configurações parciais do processo Sublevel Caving sem considerar o processo evolutivo da extração, e o dano induzido ao maciço rochoso decorrente deste processo. Esta dissertação desenvolve uma modelagem numérica utilizando o método dos elementos discretos para simular o mecanismo de ruptura e a subsidência causada pelo método de exploração Sublevel Caving, analisando o referido efeito e suas consequências na evolução do mecanismo de ruptura e subsidência no Sublevel Caving. O software comercial Particle Flow Code (PFC2D) foi selecionado para esta modelagem devido à capacidade de simular, em um evento de excesso de tensão, o fraturamento do maciço rochoso e sua desintegração, desta forma, originam-se o fluxo do material e os deslocamentos em grande escala, os quais são considerados fenômenos físicos dominantes que regem a formação da subsidência e fraturamento num processo Sublevel Caving. Os resultados obtidos nesse estudo mostraram-se satisfatórios, reproduzindo adequadamente a superfície de subsidência induzida por Sublevel Caving, conseguindo-se uma simulação física realista da sua evolução desde o início do fraturamento até à subsidência final. / [en] The Sublevel Caving Method is one of the most massive extraction methods used in underground mining industry worldwide and is considered by the mining industry as one of the natural replacements of the current open cut mines in the near future. A Sublevel Caving operation requires that the rockmass surrounding the orebody continually fails and moves into the void created by ore extraction. This dissertation develops a modeling using the discrete element method to simulate the failure mechanism and subsidence caused by Sublevel Caving method. Analyses reported in the literature consider only partial configurations of process Sublevel Caving, without taking into consideration the excavation evolution process, and damage induced to the rock mass resulting from this process. This dissertation analyzes this effect and its consequences on the evolution of failure mechanism and subsidence in Sublevel Caving. Particle Flow Code (PFC2D) was selected for modeling because of its ability to simulate, if the event of excess stress, fracturing and disintegration of the rock mass and large-scale deformation and material flow, to be simulated, which are believed to be the dominant physical phenomena governing the formation of subsidence and fracturing of Sublevel Caving. The results obtained in this study were satisfactory, reproducing properly the surface subsidence induced by Sublevel Caving, allowing physically realistic simulation of its evolution since the beginning of the fracturing to final subsidence.

Sublevel caving is an underground mass mining method used for extracting different types of ores from the earth crust. Mines using sublevel caving (SLC) as the primary mining method are generally highly mechanized with standardized and independent unit operations. Different unit operations (drilling, blasting, loading and transportation) are performed in isolation with each other which leads to standardized procedures and safe operation. Loading of the material from the production face in sublevel caving is facilitated by the flow of material under gravity into the production face. A large amount of material is loaded from a limited opening termed as the draw point which creates challenges for the mining method.   Material flow in SLC has been studied extensively in the past five decades and different methods have been used to simulate material flow in caving operations. Physical models of different scales has been designed for simulating material flow by using sand, gravel or rocks and studying the movement of material inside the model. Initial physical models showed an ellipsoidal zone above the draw point from which material flowed into the draw point. However, subsequent physical modelling results disagreed with this notion of material flow. Numerical modelling techniques have also been applied to simulate material flow. Currently, marker trials are being used to understand material flow in SLC. Markers (numbered steel rods, RFID enabled markers) are installed in boreholes drilled inside the burden of a production ring and based on the recovery sequence of markers, material flow is predicted. Results from physical models, numerical models and marker trials along with mine experience have been used in the past to optimize mine design and draw control for SLC operation. The results from latest marker trials highlight the chaotic nature of material flow and the unpredictability associated with material flow simulation.   In caving operations, draw control deals with the question of when to stop loading and regulates the loading process by providing the information on when to stop loading. The decision to stop loading a blasted ring and proceed to blasting the subsequent ring is a critical decision made in a SLC operation. If a draw point is closed early then ore is lost in the draw point which cannot be conclusively recovered at the lower levels and if delayed the mine faces greater dilution and increased mining costs. A study of the various draw control strategies used in sublevel caving operations globally has also been done to describe the present state-of-art. An analysis of the draw control and loading operations at the Malmberget and Kiirunavaara mines is summarized in the thesis using information collected through interviews, internal documents, meetings, and manuals. An optimized draw control strategy is vital for improving ore recovery and reducing dilution in SLC. Based on the literature review and baseline mapping study, a set of guidelines for designing a new draw control strategy has been listed.    In the present scenario of fluctuating metal prices and increasing operational cost a new draw control strategy is needed which is probabilistic in nature and can handle the uncertainties associated with caving operations. A draw control model which is probabilistic in nature provide a scenario based solution and can be used to test different draw control strategy before performing mine test. A framework for a probabilistic draw control model along with its application for draw control optimization has been discussed here. An effective draw control requires a constant monitoring system and a constant calibration of the loading criteria’s through draw point monitoring for reducing dilution and improving ore recovery. / Improved resource efficiency through dynamic loading control

International Caving Study 2 and Mass Mining Technology

Memoria para optar al título de Ingeniera Civil de Minas / La mayoría de los depósitos de grandes extensiones son explotados mediante minería de cielo abierto. Sin embargo, debido a que sus costos aumentan a medida que las minas se profundizan, se hace atractivo incorporar métodos subterráneos. Incluso para un mismo depósito pueden coexistir distintos métodos de explotación, siempre que sus operaciones no interfieran entre sí. Lo anterior ha motivado a buscar nuevas metodologías que permitan determinar los límites óptimos de operación incorporando planes de producción, entregando así una valorización más realista para los proyectos. En la presente memoria se desarrolla el problema de determinar el límite óptimo entre una operación a cielo abierto y un sublevel stoping con relleno (SLS). El proyecto se enmarca en un caso de estudio consistente en un depósito de oro, plata y cobre, en donde el oro es el elemento de principal interés, cuya ley promedio de es de 0.26 (ppm). Se propone una metodología que separa el estudio en 3 partes. En la primera etapa se obtiene el plan de producción de la mina cielo abierto. Luego, se obtiene el plan de producción de la mina subterránea, lo cual a su vez entrega las herramientas para definir diseño del método. Finalmente, se analiza la explotación conjunta junto con el plan de producción respectivo, definiendo los periodos de operación simultánea. La comparación de opciones de explotación se realiza mediante una evaluación económica simplificada, calculando el valor actualizado neto (VAN) de los flujos operacionales. No se incluye la inversión en equipos mina pues, se consideran del mismo orden de magnitud para las diferentes alternativas de explotación. Los resultados muestran que el VAN del rajo depende de la cantidad de estéril presente en las fases, ya que se debe anticipar el desarrollo de las mismas, haciéndolo disminuir. Por otro lado, el VAN del SLS depende del diseño utilizado (ubicación de caserones y sill pillars) por lo que una evaluación económica se hace relevante para definir el mejor diseño de la mina. Además, se deben manejar con cuidado los tiempos de cómputo en el cálculo de planes de producción del SLS, los cuales dependen del número de actividades, precedencias y niveles de la mina. Se recomienda realizar simplificaciones que no interfieran con el valor económico de las unidades de explotación y que se alineen con la temporalidad de la evaluación. La operación conjunta se analiza mediante un análisis de costos directos operacionales, lo cual permite determinar cuándo conviene explotar con cada método. No obstante, todavía existe la necesidad de herramientas que hagan una evaluación óptima de la operación conjunta. En el caso de estudio, el mayor VAN se obtiene con una mina cielo abierto de menores dimensiones. Esta decisión es sensible a los costos minas, ya que con pequeñas variaciones la decisión cambia y la explotación conjunta se torna más atractiva. La metodología planteada muestra una nueva forma de obtener resultados de explotación conjunta y de diseño óptimo del sublevel stoping. Se recomienda incluir más detalles a considerar para la obtención del plan de producción conjunto, principalmente incorporando mejoras al método creado para la mina SLS.

Sublevel caving (SLC) is a mass mining method relying on the flowability of the blasted material. The ore is blasted in slices against caved material which is mainly waste rock. The result of the confined blast is greatly influenced by the interaction between the blasted material and the caved material. During blasting both materials change characteristics; the blasted material increases its porosity and compressibility due to breakage and swelling while the caved material is compacted and decreases in porosity and compressibility. The understanding of the mechanisms involved in this process is of significant importance. The behavior of the caved material (confining material) was studied in laboratory under dynamic loading. A new apparatus was developed to conduct impact tests to simulate blasting conditions. The tested material was a blend of crushed waste rock from drift development in the Kiirunavaara mine with maximum particle size 32 mm. The material was tested for two conditions, i.e. dry and wet (pendular state), and with different impact velocities (low (5 m/s), medium (8 m/s) and high (10-12 m/s)). During the impact tests, two types of measurements were taken; dynamic measurements based on the recordings from the installed accelerometers on the machine and static measurements pre- and post-impact. Additionally, the angle of repose, the impact duration, and the fragmentation was measured. In addition to the laboratory tests, small-scale blasting tests were carried out to investigate the burden behavior in confined conditions. The blasted specimen was a cuboid magnetic mortar block and the confining material was crushed concrete with maximum particle size 16 mm. The blocks were instrumented with custom-made incremental displacement sensor. After the analysis of the results from the above experimental work, two confined pillar tests (test #1 and test #2) were carried out at the Kiirunavaara mine. The preparation work for the pillar tests involved the development of instrumentation and installation techniques. The experimental configuration contained two blastholes and measurement holes in between the blastholes drilled from the neighboring drift. Test #1 mainly focused on the evaluation of the instrumentation and techniques while test #2 was focused on the interaction between the blasted burden and the confining material. The confining material in test #1 was a blend of ore and waste material from drift development at the Kiirunavaara mine. The characteristics of the material were unknown. Test #2 was split into two parts, the confining material in the first part was the same as in the laboratory impact tests and the second part of the pillar was confined by caved masses. The instrumentation was installed in the burden of the pillars and was equipped with accelerometers and displacement sensor. Additional instrumentation was also installed in the confining material. The burden in the small-scale blasting tests reached maximum velocity 29 m/s and maximum displacement 12.6 mm. In pillar tests, the burden movement was in the range of 0.9 to 1.1 m. In both pillar tests, burden erosion material was observed in the gap between the intact and the blasted burden. This material was finer compared to the blasted burden. The origin of this material was from the vicinity of the blastholes. The results of the laboratory tests showed that the wet material exhibited larger compaction zone than that of the dry material. The wet material showed apparent cohesion close to the impact surface of the tested material. A similar observation was made in test #2 where an agglomeration of the confining material, as a result of apparent cohesion, was observed on the surface of the blasted burden. The displacement data from the instrumentation in the burden and inside the confining material showed that the compaction zone follows an inverse exponential behavior. After the blast steeper angles of repose were measured indicating higher frictional forces between the particles. Moreover, the evidence of apparent cohesion and a larger angle of repose indicated the introduction of tensile strength in the material. The mass of the confining material was compressed elastically and plastically during the blast. After the blast, the material recovered its elastic deformation and pushed the blasted burden backward as observed in the small-scale blasting tests and the pillar tests. At this stage, the burden erosion material was compacted. Hence, there were 3 materials, i.e. burden erosion material, burden and confining material, which were compacted with different compaction rates. This condition promotes interlocking of the particles in the materials. If this behavior is correlated with a production SLC ring, then it indicates disturbances in flowability of the blasted material.