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Evaluación de la estabilidad pseudoestática para botaderos apoyados sobre laderas coluviales considerando un evento sísmico severo, ubicado en la Mina Chépica, Región del Maule
Abstract
Evaluation of pseudostatic stability for waste rock dumps supported on colluvial slopes considering a severe seismic event, located in the Chepica Mine, Maule Region.
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Resumen Los materiales granulares gruesos (MGG), definidos con tamaños máximos (TM) de partículas mayores a 7,5 cm (3") de diámetro, están siendo cada vez más demandados tanto en proyectos de Ingeniería Civil como de Minería. Sin embargo, la caracterización geotécnica de MGG es un tema que continúa en investigación. Así, en este trabajo se analizan 4 temas asociados a las propiedades geotécnicas de MGG: (1) Clasificación de MGG según su constitución y origen (Suelos gruesos de origen sedimentario, y apilamiento de rocas no afectadas por erosión geológica o transporte). (2) Uso de un coeficiente de uniformidad que utiliza un D80 y D10 (Cu* = D80/d10). (3) Definición de granulometría gruesa, diferenciando MGG que poseen TM entre 7,5 cm a 100 cm diámetro (ej. suelos gruesos aluviales/fluviales) de MGG tipo bloque con TM mayores a 100 cm (p. ej. materiales de botaderos mineros) (4) Elección de la densidad de confección y DR% en muestras escaladas al usar el método de granulometría paralela.
Abstract: Coarse granular materials (CGM), defined with maximum sizes of particles greater than 7.5 cm (3 ") in diameter, are being increasingly demanded in both Civil Engineering and Mining projects. However, the geotechnical characterization of CGM is a topic that continues in research. Thus, 4 topics are analyzed in this work in terms of CGM geotechnical properties: (1) Classification of CGM according to its constitution and origin (coarse soils of sedimentary origin, and rock-piles not affected by geological erosion or transport). (2) Use of a uniformity coefficient using a D80 and D10 (Cu * = D80/D10). (3) Definition of coarse gradation, differentiating CGM having maximum particle between 7.5 cm to 100 cm diameter (e.g. alluvial/fluvial coarse soils) from CGM with maximum size greater than 100 cm (e.g. mining waste rock materials). (4) Choice of the confection density and RD% in scaled samples when using the parallel gradation method.
Resumen En este trabajo, la efectividad del método de granulometría paralela es revisado desde sus primeras aplicaciones en la década de los 60' hasta el año 2017 desde un enfoque de resistencia al corte y comportamiento de MGG. Las principales conclusiones son las siguientes: a) Aunque esta metodología fue presentada en detalle en 1964, las principales investigaciones experimentales que la han corroborado fueron publicadas desde el año 1998 hasta la fecha. b) Esta metodología ha sido corroborada en suelos gruesos de origen fluvial/aluvional, enrocados de roca sedimentaria y rocas chancadas de alta resistencia a la compresión uniaxial c) La metodología no ha sido corroborada de manera efectiva en enrocados con partículas de tipo ígneas y metamórficas, debido a la fuerte influencia de las fracturas discretas en la roca, disminuyendo la resistencia de las partículas a mayor tamaño. Así, este trabajo presenta recomendaciones en el uso adecuado de esta metodología en especial para MGG.
In this work, the effectiveness of the PGM is reviewed from its first applications in the decade of the 60' until now in terms of a strength approach and CGM behavior. The main conclusions are the following a) Although this methodology was presented in detail in 1964, the main experimental investigations that have corroborated it were published from 1998 to date. b) The effectiveness of the methodology has been corroborated mainly in coarse soils of fluvial/alluvial origin, sedimentary rockfill and high strength crushed rocks. c) The methodology has not been corroborated effectively in igneous and metamorphic rockfill materials, due to the strong influence of the discrete fracture network in the rock, which decreases the strength of larger particles. Thus, this paper presents recommendations on the proper use of this methodology, especially for MGG, which are used to a large extent in civil engineering (e.g. rockfill dams) and in the mining industry (e.g. waste rock dumps).
Modern large-scale open pit mines move hundreds of thousands of tonnes of material daily, from the loading sources to the destination zones, whether these are massive mine dumps or, to a lesser extent, to the grinding mills. Mine dumps can be classified as leach or waste dumps, depending upon their economic viability to be processed in-place, a condition that has experienced great progress in the last decades and has reconfigured the open pit haulage network with an increase in the number of dumps. Therefore, new methods for dump design optimization are of the highest priority in mine planning management. This paper presents a methodology to model and optimize the design of a dump by minimizing the total haulage costs. The location and design of these dumps will be given mainly by the geological characteristics of the mineral, tonnage delivered, topographical conditions, infrastructure capital and transportation costs. Spatial and physical design possibilities, in addition, provide a set of parameters of mathematical and economic relationship that creates opportunities for modelling and thus facilitates the measurement and optimization of ultimate dump designs. The proposed methodology consists of: (1) Formulation of a dump model based on a system of equations relying on multiple relevant parameters; (2) Solves by minimizing the total cost using linear programming and determines a “preliminary” dump design; (3) Through a series of iterations, changes the “preliminary” footprint by projecting it to the topography and creates the ultimate dump design. Finally, an application for a waste rock dump illustrates this methodology.
A ground‐motion prediction equation for the horizontal component of the response spectral values from the Chilean subduction zone is developed. The dataset contains 3774 recordings from 473 earthquakes, including the latest megathrust events that occurred in the country (i.e., 2010 Mw 8.8 Maule, 2014 Mw 8.1 Iquique, and 2015 Mw 8.3 Illapel). The functional form for the median model follows the proposal by Abrahamson et al. (2016). Site effects are estimated based on VS30. An additional model is built using only ground motions associated with measured values of VS30 and reliable Mw estimates (termed the high‐quality [HQ] model). The standard deviation of the HQ model is much lower than the main model, particularly the component of the standard deviation that corresponds to site‐to‐site variability, indicating that better site characterization can significantly reduce the overall uncertainty in ground‐motion estimation.
This article is about an applied research on a natural slope located in the fifth region of the country, where one of the objectives was to compare different methods of calculating slope stability under static and pseudostatic conditions. In the latter case, we considered two major earthquakes that have occurred in Chile, such as the 1985 Valparaiso earthquake and 2010 Maule earthquake, with magnitudes of Mw = 8.0 and Mw = 8.8, respectively. Comparison of the results was carried out by obtaining safety factor of potential failure surfaces, through the use of software GeoSlope considering the worst case and using the models proposed by Fellenius, Bishop and Janbu (method of slices). As a result, it was possible to observe the influence of the earthquake on a finite slope, which depends on the Richter scale earthquake, and the values of the coefficients of seismic acceleration (horizontal and vertical).
RESUMEN Se proponen las primeras fórmulas de atenuación de aceleraciones, velocidades, desplazamientos, horizontales y verticales máximos de registros de terremotos chilenos. Las fórmulas propuestas son las primeras que consideran las diferencias entre los tipos de sismos más característicos de Chile –interplaca tipo thrust e intraplaca de profundidad intermedia-, además son las primeras en separar las fórmulas por tipo de suelo, utilizando una clasificación dinámica de suelo basada en la velocidad de onda de corte Vs en 'rocas y suelo duro' para 1500 [m/seg] > Vs > 360 [m/seg] y 'rocas duras' Vs > 1500 [m/seg]. Las fórmulas de atenuación de terremotos intraplaca presentan valores más altos que los terremotos interplaca en zona epicentral pero se atenúan más rápido. Los valores obtenidos en roca o suelo duro son más altos que los estimados por las fórmulas de roca dura. Los coeficientes de correlación que se obtienen para las fórmulas de terremotos son altos al compararlos con fórmulas similares. Las curvas se encuentran calibradas para datos de grandes terremotos como el terremoto interplaca de Chile Central de 1985 (M = 7.8) y el terremoto intraplaca de Tarapacá 2005 (M = 7.9).
Chile is one of the most seismically active countries in the world, having witnessed several large earthquakes that produced human and material losses; seismic hazard estimation is one of the most used tools to prevent such losses. The present study reviews the state-of-the-art of the probabilistic seismic hazard, comparing 3 different approaches and adapting them to central Chile. We include a series of new findings, such as the definition of the main seismogenic sources (interplate, intermediate-depth intraplate, and crustal earthquakes), new estimations of Gutenberg-Richter laws, and the use of specific attenuation laws for each one of them. Considering this information, we compute maps showing the expected peak ground horizontal acceleration (PGA), given a certain probability and time period where is observed not only the influence of interplate earthquakes, but also the effect of intermediate-depth intraplate and crustal earthquakes. For the Santiago Metropolitan área we obtain valúes for PGA of 55% g for a return period of 475 years and 72% g for a return period of 1950 years; only 13% lower than those observed on the coast (63% g and 83% g, respectively).
Synopsis
Within the framework of limit equilibrium methods of stability analysis, no restriction need be placed at the outset upon the shape of the possible slip surface. In many cases, the critical surface may deviate significantly from a circle or a plane and therefore a method that facilitates the analysis of surfaces of arbitrary shape is of interest. A method for doing this is presented. The assumptions necessary to make the problem statically determinate are discussed. The solution of the governing equations ensures that all equilibrium and boundary conditions are satisfied. The method has been programmed for a digital computer and some examples of its application are given. Comparisons are also made with other methods of analysis.
Dans la cadre des méthodes d'équilibre limite d'analyse de stabilité, il n'y a pas besoin d'imposer de restrictions au départ sur la forme de la surface de glissement éventuelle. Dans bien des cas, la surface critique peut dévier d'une manière significative d'un cercle ou d'un plan at par conséquent une méthode qui facilite l'analyse des surfaces de formes arbitraires présente un intérêt. On présente une méthode pour accomplir cela. On discute des hypothèses nécessaires pour que le problème soit déterminé au point de vue de la statique. La solution des équations dominantes garantit que toutes les conditions d'équilibre et de limite soient satisfaites. La méthode a été programmée pour une calculatrice digitale et on donne quelques examples de ses applications. D'autres méthodes d'analyse y son comparées.
Flow systems in unsaturated waste rock piles were simulated using a two-dimensional numerical model (HYDRUS). The conceptual
models are based on homogeneous (unstructured) waste piles, and on structured piles that include either horizontal or inclined
fine-grained layers within a coarser host material, forming a capillary barrier system. The approach considers fully transient
conditions and uses observed climatic data from a mine site in northern Quebec, Canada. All physical properties of the porous
media, including the water retention curves, were obtained from measured data. Different geometric configurations were tested
to determine their effect on moisture distribution and water flow, which ultimately control the potential for acid rock drainage
(ARD). The simulations begin with a relatively dry initial condition under hydrostatic equilibrium. After an initial transient
period, the simulated internal moisture distribution became periodic with a regular pattern of seasonal fluctuations. The
simulations suggest that flow can be controlled in such systems using inclined fine-grained layers that retain and divert
moisture due to capillary barrier effects. With horizontal layers, the local flow regimes become unstable, causing vertical
preferential flow zones to develop below the barriers wherever the local water pressure first exceeds the entry pressure of
the underlying coarser material. In this scenario, ARD production can remain high since a large fraction of the internal pile
is being flushed. A shallow downward slope in the layers forces drainage toward the outer boundary and maintains lower saturation
in the centre of the pile, thus potentially reducing the amount and mobility of ARD.