Effect of dip on pillar strength

© The Southern African Institute of Mining and Metallurgy, 2018. Pillars are commonly left in underground mining, either for secondary extraction after the primary stopes have been filled or to maintain the overall macro-stability of the mine during its useful life by supporting the overburden. The dip, dimensions, and geological features of an orebody determine the mining method used. If pillars are used, the orientation of pillars can vary from horizontal to vertical and anything in-between. The pillars left in underground mines can be loaded axially or obliquely (axial and shear components) depending on their orientation and that of the field stresses. Empirically established methods or numerical modelling are used to design mine pillars. We conducted studies on square and rectangular pillars under normal and oblique loading. The strengths of the horizontal pillars were calibrated to the Lunder and Pakalnis pillar strength, while the strength of the inclined pillars was obtained in reference to the horizontal pillar performance. The failure modes are described for inclined pillars at different width to height ratios. Brittle failure was determined to be the dominant failure mode in the inclined pillars. Rectangular pillars are beneficial only when the length is increased along the dip at higher inclinations and with W/H ratios greater than 1.5

Laboratory and numerical investigation on strength performance of inclined pillars

Pillars play a critical role in an underground mine, as an inadequate pillar design could lead to pillar failure, which may result in catastrophic damage, while an over-designed pillar would lead to ore loss, causing economic loss. Pillar design is dictated by the inclination of the ore body. Depending on the orientation of the pillars, loading can be axial (compression) in horizontal pillars and oblique (compression as well as shear loading) in inclined pillars. Empirical and numerical approaches are the two most commonly used methods for pillar design. Current empirical approaches are mostly based on horizontal pillars, and the inclination of the pillars in the dataset is not taken into consideration. Laboratory and numerical studies were conducted with different width-to-height ratios and at different inclinations to understand the reduction in strength due to inclined loading and to observe the failure mechanisms. The specimens’ strength reduced consistently over all the width-to-height ratios at a given inclination. The strength reduction factors for gypsum were found to be 0.78 and 0.56, and for sandstone were 0.71 and 0.43 at 10? and 20? inclinations, respectively. The strength reduction factors from numerical models were found to be 0.94 for 10? inclination, 0.87 for 20? inclination, 0.78 for 30? inclination, and 0.67 for 40? inclination, and a fitting equation was proposed for the strength reduction factor with respect to inclination. The achieved results could be used at preliminary design stages and can be verified during real mining practice

Estudio de Factibilidad para la Implementación de una Empresa Dedicada a la Producción y Distribución de Nitrógeno Líquido

La necesidad de resolver este problema es que actualmente no se cuenta con un mercado satisfecho, hay muchas empresas, que necesitan este producto para el funcionamiento de sus negocios, pero debido al alto costo y a un servicio deficiente que actualmente se ofrece, dejan de invertir más en sus negocios y generando un costo elevado en sus operaciones. Para resolver esta necesidad se determinó que el nitrógeno es un producto extremadamente frio a una temperatura de -196 °C, el valor actual de venta de nuestro principal competidor es de S/ 22.40 soles y otros distribuidores lo venden a un precio de S/ 14.00 soles, Así que se desarrolló un estudio de mercado y se determinó que en la ciudad de Arequipa en total 60000 empresas que son nuestro mercado potencial, pero también tenemos a 7 distribuidores que serán nuestros principales clientes también se determinó que el crecimiento global es de 5.98 % y en base a este crecimiento se determinó la ubicación de la empresa en el distrito de Cerro Colorado junto con un estudio técnico, las demás localizaciones competidoras son sachaca que según el método de Brown y Gibson indica una puntuación de 0.248 , parque industrial con 0.150 y Hunter con 0.262, todas frente a 0.340 que es del distrito de Cerro Colorado el lugar escogido para nuestra empresa ; la organización está sujeta a él régimen general siendo una SAC ya que estamos sujetos a una contabilidad completa pagando el 18% IGV, el 30% IMP y porque nuestra empresa está sujeta a un ingreso no mayor de 150 UIT, cada UIT equivale a S/. 4050 soles lo que correspondería a S/. 607500 Soles al año y nosotros estaríamos con un total de S/.200000 aproximadamente, también se elaboró un plan de marketing y se determinó que, para ser competitivos se tiene una producción de 1660 kilos mensuales con una pureza del 99.99% garantizado por nuestro proveedor quien nos venderá la maquinaria para lograr este objetivo, este proyecto no es contaminante por lo que no representa un peligro ya que el rango de impacto según la ley es mínimo, la etapa de construcción será realizado por una empresa que cuente con un plan de seguridad mostrando indicadores y una matriz IPERC cuantificando los impactos, ALTO en un rango de 9-10, MEDIO 5-8, BAJO 1-4, una vez puesta en marcha el funcionamiento de la planta, se elaborara el plan de SST. En el estudio financiero se determinó que se necesita una inversión de S/ 334,173.50 soles, el 80% será financiado por INTERBANK y el otro 20% representa el capital de los accionistas, siendo el periodo de pago por 5 años, y el tiempo de recuperación de la inversión de nuestro proyecto en el tercer año, que lo hace rentable ya que el VAN 409,356.94 tiene un valor positivo y los indicadores nos indican que es viable nuestro proyecto. Palabras clave: Nitrógeno Líquido Inversión CriogénicoTesi

Performance of inclined pillars with a major discontinuity

Discontinuities are an inherent part of the rock mass and majorly affect the stability of the excavation skin and pillars. The dip of the discontinuities and their properties also have a significant effect on the strength of the pillars. Empirical approaches are commonly used to determine the pillar strength but can overestimate the strength and don't consider the inclination of the pillars and the strength reduction caused by discontinuities. Numerical modeling is a powerful tool and if calibrated can be used to evaluate the strength of the pillars with discontinuities having a range of properties. The effect of a discontinuity on inclined pillars was conducted which has been seldom considered in evaluating the pillar strength. Three-dimensional vertical pillars were simulated, and the pillar strength was calibrated to accepted theoretical results and then the discontinuities were introduced in different pillar inclinations with distinct width to height ratios to gain an insight into the effective pillar strength reduction. Based upon the results, it was found that the discontinuities have a significant effect with the increase in the inclination of the pillars even at a higher width to height ratios

Rapport sur les fouilles exécutées à Lille à l'emplacement de l'ancienne collégiale St-Pierre (Avril-Juillet 1966)

Jessu Philippe. Rapport sur les fouilles exécutées à Lille à l'emplacement de l'ancienne collégiale St-Pierre (Avril-Juillet 1966). In: Revue du Nord, tome 48, n°191, Octobre-décembre 1966. pp. 598-601

Investigating the Performance of Hard Rock Pillars with Different Width to Height Ratios and the Effects of Inclination, a Discontinuity and Blasting

Pillar design, a challenge in underground hard rock mines, contributes to catastrophic failure or economic loss based on its failure mechanism. Factors influencing the pillar failure mechanisms such as pillar inclination, presence of discontinuity and blasting effects were investigated with the help of laboratory tests and numerical analyses to create a design structure. Lastly, the pillar designs were evaluated by developing strain based monitoring method for pillar classification and pillar optimization

Numerical Analysis of Coal Pillar Stability on Variable Weak Floor with Paste Backfill

This thesis investigates the stability of coal pillars under realistic conditions of varying weak floor thickness with and without the use of paste backfill. Weak floor strata underlying coal seams are common in the Illinois Basin. They consist mainly of underclay, which is a gray, argillaceous rock that usually occurs immediately beneath beds of coal. Underclay thickness may vary from less than a foot to twenty feet at different locations in the basin (Grim and Allen, 1938). Locally, underclay thickness may vary gradationally over a distance of two pillars. Even though weak floor thickness is not consistent (Gadde, 2009), most research to date has focused on parametric studies with a fixed underclay thickness and formulated coal pillar designs on the basis of the maximum underclay thickness measured in the field. Therefore, it is necessary to investigate more realistic field conditions and quantify the influence of a gradated weak floor thickness using additional parametric studies. This research is primarily numerical modeling incorporating various constitutive models and using some calibration. Therefore, the two dimensional plane strain finite difference model in FLAC 3D is employed to carry out parametric studies on gradated weak floor conditions. Underclay exhibits Mohr Coulomb elastic plastic behavior; hence, the Mohr Coulomb constitutive model is used for the behavior of overburden, coal, and floor. Well-calibrated numerical models can assist in understanding load and failure processes provided that coal, overburden, and weak floor are modeled with sufficient realism. The theoretical approach considers a friction angle of 0° to calculate the load bearing capacity of the weak floor for design of pillars with long-term stability, even if the weak floor has a non-zero friction angle. The stiffness of the weak floor increases with an increase in friction angle (Gadde, 2009; Kostecki and Spearing, 2015). As stiffness increases, a point can be reached where floor bearing capacity exceeds coal pillar strength and coal pillar strength becomes the governing factor. For this scenario, the Mohr Coulomb strain softening model is more realistic in estimating loads carried by coal pillars in the post-failure stage. The three-dimensional Mohr Coulomb strain softening model in FLAC 3D is employed to study qualitatively the floor response in strain softening coal behavior conditions. Maintaining stable coal pillar responses has been a challenge for the coal mining industry due to attempts to increase the primary extraction ratio. Presently, the best available solution seems to be backfilling when considering short-term pillar stability (i.e., less than the long-term factor of safety) with increased extraction ratio. There are various types of mine backfill that have benefits to the mining industry depending on the application, but paste backfill produced from total mill tailings containing no free water is the best option for post-mining ground control in room-and-pillar mines as it prevents weakening of the floor and will not contaminate the ground water. The influence of paste backfill on floor bearing capacity and coal pillar response is studied with numerical modeling using the same constitutive models already identified. Finally, an economic analysis is carried out to look at cost implications of a proposed system with backfill