Ingeniero Civil / Los métodos empíricos de clasificación geomecánica son ampliamente usados para la estimación de los requerimientos de soporte en túneles, particularmente en condiciones de rocas diaclasadas. En general, las metodologías empíricas se aplican en las primeras etapas del diseño, cuando no se dispone de suficiente información geotécnica-geológica o como una herramienta adicional para apoyar el juicio de ingeniería. El objetivo de esta investigación es asistir a ingenieros en la identificación de los principales parámetros de control asociados a estas clasificaciones y los respectivos indicadores de estabilidad proporcionados por estos métodos en comparación con los factores de seguridad obtenidos con modelos analíticos y numéricos. Esta memoria presenta los resultados de un estudio comparativo de los requerimientos de soporte para la excavación de una sección de túnel tipo herradura de 10mx10m (~90m2), obtenidos con diferentes métodos empíricos, métodos analíticos (estabilidad 3D de cuñas) y numéricos (método de elementos finitos). Los métodos empíricos considerados son RMR, Q y RMi, el método analítico de estabilidad de cuña usado es a través de Unwedge y el software de elementos finitos es Phase2D (Rocscience Inc.). Los escenarios consideran macizos rocosos diaclasados a muy diaclasados, condición seca, esfuerzos bajos a intermedios y mecanismos de falla controlados principalmente por las condiciones estructurales y gravitacionales. Los resultados indican que las metodologías empíricas son más sensibles a parámetros de volumen de bloque que a los de calidad de diaclasas, que el método Q propone menores requerimientos de soporte y que los factores de seguridad obtenidos con Unwedge aumentan drásticamente con el uso de shotcrete. Dado que la sección de túnel no se considera en el diagrama GSI, la definición de diaclasado y muy diaclasado no captura apropiadamente el comportamiento esperado de los modelos de elementos finitos según Phase2D.

Rock wedge stability is a common concern in underground excavations. Since the wedge stability influences the support design, it is important to use a wedge stability analysis method that can capture factors like excavation geometry, joint parameters and properties, rock mass properties, rock cover, and stress field as accurately as possible. This thesis compared the Limit Equilibrium Method (LEM) and the Discrete Element Method (DEM) using the software UnWedge (LEM) and 3DEC (DEM). The objectives included studying how factors like excavation and joint geometry, stress field, rock cover, and rock mass properties could be considered by the methods and how that affected the wedge stability and support design. Nine different analysis cases were defined with the aim of capturing wedge stability analysis parameters representable for both the civil engineering and mining sector. The study found that 3DEC allows for more accurate modelling of excavation and joint geometry, considering joint density and full 3D geometries, while UnWedge has limitations in creating intersecting tunnels and does not consider joint density. Only 3DEC, with stress redistribution and a plastic material model, captures rock mass failure mechanisms other than wedge failure. Based on the study, it is recommended to use DEM for situations where the excavation geometry cannot be assumed as two-dimensional with constant cross-section, and, when stress-induced rock mass failure is expected, use DEM with stress redistribution. It is also recommended to use information about joint lengths if available and apply engineering judgement when studying results of wedge volume and support force.

Study of Production Drifts Stability and Assessment of Reinforcement Requirements at LKAB Konsuln Test-Mine Levels 436 and 486 Using Geologic Structures Data, and Modelling Software - Dips and Unwedge:  a Part of dp1 Project (Mine Layout and Technology) of the Sustainable Underground Mining (Sum) Project Oludare Joseph Olufe Global population has been on exponential increase over the past half century. The population explosion is driving massive urbanization and infrastructure developments across the globe, which result in huge demand for metals, especially steel. The trend is forecasted to continue to rise steeply in for the next two decades. This is putting enormous strain on metals mining, especially because new surface economic deposits are rare to come by. Therefore, mining is steadily going deeper in many of the mining destinations across the world.     Mining at great depths present unique challenges, particularly regarding stability of excavations at depths. Rock falls, rock burst, excavation collapse are common occurrences associated with deep mining. In regions with high seismicity potentials the frequency and consequences could be very high. Over the past decade ground instability has become a significant challenge confronting mining at LKAB deep mines. There had been incidents that resulted in long term closure of sections of the mines, with resultant adverse economic impacts. More undesirable is loss of live of personnel.     The study was conducted at the Konsuln test mine levels 436 and 486, aimed to investigate the impacts of geologic structures on excavations instability at depths, at the Kiruna iron ore mines, on one hand.  And on the other hand, evaluate the influence of geologic structures on ground reinforcements at the mine. Structural data were collected and analysed using Dips program to define orientation of major structures. The results were used for wedge analysis and excavations stability modelling using Unwedge program. Important rock mechanical parameters were defined based on data provided, and others based on literatures. A design factor of safety of 1.5 was used.     Results from the study established that structures have significant impact on excavations instability at the Konsuln mine. 100% of the production drifts studied has minimum of four wedges formed in its perimeters. Out of this approximately 37% has factor of safety lower than 1.5. Evaluation of reinforcements (shotcrete and rock bolts) implemented in the mine found that approximately 15% of the total wedges formed in the production drifts has factor of safety less that 1.5 after both shotcrete and rock bolt reinforcements had been implement. Also, approximately 5% of the total wedges has apex height longer the rock bolt length.     It was therefore concluded that structurally induced instability is a major contributor to excavations instability at the Kiruna mine. The study approach presented a new methodology to understand and provide robust solution to ground instability problem at the mine.

Sublevel caving operations at great depths are subjected both to large stress concentrations that are redistributed as the mining front progresses and to mining-induced seismicity. This is the case for Kiirunavaara mine, Sweden’s largest underground mine. Since the mine was declared seismically active in 2007 / 2008, large rockfalls controlled by structures have happened in many parts of the mine, despite the use of rock support systems designed for bearing dynamic loads. A novel layout for sublevel caving operations, internally named “fork layout” is being tested at a satellite mine. This layout was conceived to place the ore-parallel longitudinal footwall drifts further away from the contact between the orebody and footwall drifts. That way, the differential stresses that generate stress-related damages are expected to be reduced. However, the effect of implementing the fork layout on the hazard potential for structurally controlled rockfalls has not been studied in detail yet. Large rockfalls that occurred in different parts of the mine were analysed with respect to their structures, location of the damage event and type of excavation. The majority of these occurred at footwall drift intersections. Information from damage mapping and seismic events that triggered these rockfalls was used to generate a conceptual model that illustrates the relative spatial relation between the seismic source and damage location. In addition, the seismic source parameters of the events that triggered these rockfalls were processed using scaling laws to obtain ground motion parameters such as peak particle velocity and acceleration at the damage site. The effect of implementing the fork layout on rockfall hazard was tested in the intersections between footwall drifts and crosscuts (FD-CC), and intersections between access and footwall drifts (AD-FD) in two production blocks, using the traditional layout for sublevel caving mining as a point of comparison. Two different fork layouts were tested, FD-CC at 80° (or AD-FD at 100°) and FD-CC at 70° (or AD-FD at 110°). Structural data available from face mapping and oriented core logging was used to define predominant joint sets at the investigated blocks. Using the structural input, wedge volumes at the intersections were modelled deterministically and probabilistically in Unwedge. The variations in wedge volumes formed at the intersections between layouts were used as a proxy for rockfall potential, meaning that if a layout reduced the wedge size, the smaller the rockfall hazard if triggered by a seismic event, and vice versa. It was concluded that most rockfalls at the FD-CC intersections are controlled by structures from three major joint sets. It was observed that rockfalls at FD-CC intersections occurred more often at certain footwall drift orientations. Many seismic events that triggered these rockfalls are located close to the ore passes and generated ground accelerations between 0.5 to 10 times the gravity acceleration. Implementing fork layouts with FD-CC at 80° intersection angle generates larger wedges than the traditional layout and thus, scenarios with a higher rockfall hazard. On the other hand, using fork layouts with FD-CC at 70° intersection angle reduces wedge size at the southern FD-CC intersections; hence, the rockfall hazard is reduced in these intersections. In the northern FD-CC intersections, the wedge volumes are increased and thus, a higher rockfall potential is generated in these intersections. AD-FD at 110° intersection angle generates also a smaller rockfall hazard than the traditional layout in both production blocks.