There is little process control employed at aggregate crushing plants and essentially no optimization at the primary or jaw crushing stage. Jaw crusher selection is very dependent on the subjective judgment/experience of individuals, the characterization of rock material using inadequate and unrepresentative tests, and the desire to limit secondary breakage, resulting in the conservative selection and operation of jaw crushers. A method for predicting the power consumption, product size, and volumetric capacity of jaw crushers based on fracture toughness has been proposed in this study. A new fracture toughness test, the Edge Notched Disk Wedge Splitting test, has been developed and verified in order to rapidly assess the fracture toughness of six quarry rocks. A High Energy Crushing Test system has been used to simulate the operational settings of a jaw crusher so that comparison of fracture toughness, specific comminution energy, and breakage distribution could be performed. The results indicate that the specific comminution energy required to reduce a rock particle to a given size increases with fracture toughness. The breakage distribution has also been shown to be dependent upon fracture toughness as long as the elastic modulus is taken into account. Laboratory jaw crushing experiments show that the capacity of a jaw crusher is dependent upon fracture toughness and the elastic modulus. Models for the prediction of power consumption, breakage function/product size, and volumetric capacity have been developed based on these results. At the experimental level, the models were able to predict the specific comminution energy to within 1% and t10 (characteristic crushing parameter) to within 10%. Prediction of the product size distribution produced by a lab-scale jaw crusher, for four different rocks, was within ± 5% (in terms of percent passing). The models allow for the selection of a jaw crusher based on the nature of the rock being broken and the average amount of size reduction done on the feed material. The models can also be used to optimize feed and operational settings, as well to determine the product size produced for a given rock and reduction ratio. / Ph. D.

This report is to investigate the use of fracture mechanics parameters (fracture toughness, specific work of fracture) to characterize comminution process. Comminution is a very important industrial process and is extremely low in efficiency. Establishment of a crushing index based on fracture mechanics principles is of great significance for improved machine design and enhanced efficiency. Single particle fracture study has been reviewed because it is considered the most elementary process in and provides the basis for comminution. <p>Rock fragmentation can be best described by fracture mechanics principles and concepts. The most fundamental concept in fracture mechanics is fracture toughness. Extensive review has been done on the fracture toughness application to rock fragmentation problems, and has found it has not been successfully used in comminution process. Further study is necessary to investigate the link between comminution and fracture toughens. Interrelation of fracture. toughness with other rock properties has been studied. Loading rate effects on fracture toughness has also been reviewed. <p>Fracture toughness testing for rock materials has also been studied. The SCB (Semi-Circular Bend specimen) method has been selected for its sound analytical background and ease of operation. A experimental proposal is made based upon the survey results. Single particle fracture is proposed to be conducted on the Allis-Chalmers High Energy Crush Test System, which, compared with other test apparatus, more closely simulates the actual crushers. Detailed procedures on how to use the test system has been given in the report. / Master of Science

This research is carried out to better understand the nature of the rock mass and to have a better anticipation of rock fragmentation before blasting the rock mass. Current practices of assessing rock mass usually involve techniques that focus on the surface or outcrop of the rock mass such as scanline surveys, window surveys, photogrammetry and laser scanning etc. These techniques generally lack the ability of providing sufficient information about the rock mass as well as bear various inherent constraints such as safety issues, time requirements, user biasness, equipment requirements and reproducibility of results. Similarly, the rock fragmentation is predicted using different mathematical equations known as fragmentation models. However, these models ignore some key factors that significantly affect the nature of fragmentation such as chargeability of blastholes, drilling information e.g. borehole deviation and require numerous rock parameters which are not well known in most cases. These models are often site-specific and are mostly developed for surface mines. Therefore, their application in underground mining is not so common. The aim of this research is to investigate the possibility of eliminating the constraints and supporting the current practices of rock mass assessment and rock fragmentation prediction. In this regard, drill monitoring technique has been selected as a potential tool for analysing the rock mass and forecast the rock fragmentation. To test the selected technique, measurement while drilling (MWD) data was collected from three different mines. The variations in MWD data were analysed to identify different zones and structures present inside the rock mass. The results were compared to 3D images obtained by close-range terrestrial digital photogrammetry for validation, which showed a close agreement with each other. Similarly, MWD data was used to classify the rock mass into five different classes i.e. solid, slightly fractured, highly fractured, having cavities, and major cavities in a sublevel caving operation. The loading operation of the blasted rock was filmed and digital images of LHD buckets containing blasted rock were extracted from the video recordings. The blasted rock inside the buckets were categorized as fine, medium, coarse and oversize fragmentation based on their median fragment size (X50). A statistical analysis was carried out to see the correlation between MWD based rock mass classes and fragmentation classes. The results showed that fine and medium size fragmentation has better correlation and can be predicted with higher accuracy using MWD data as compared to coarse and oversize fragmentation. The results suggest that the drill monitoring technique has the potential to assess rock mass as well as predict rock fragmentation to some extent. It can be used to differentiate between a weak or strong rock mass or between a fractured or competent rock mass. It can be used to differentiate between joints, cavities or foliations etc. It can also be used to predict finer and medium size fractions of the blasted rock with reasonable accuracy. However, the coarser and oversize fragmentation didn’t have a reliable correlation with MWD data. The potential of using drill monitoring technique for rock mass assessment and rock fragment prediction can be further explored and validated using other established rock mass and fragmentation assessment techniques. It can largely overcome the time, cost and safety constraints associated with the methods already in practice.

Blasting is one of the most important stages in the productive process of a mine due to its direct impact on rock fragmentation, which determines the degree of productivity of operations and the extraction costs generated. In this scenario, an optimized methodology is presented for designing blasting meshes by using mathematical models that help calculate the geometric parameters of a blasting mesh, such as burden, considering the variables of the rock mass and the type of explosive to measure its impact on rock fragmentation and loading productivity (tons/hour). The main advantage of this method is the reliability of the design, which takes into account a greater number of variables that influence fragmentation and uses the principle of distribution and amount of energy in an optimal way. The results obtained in the case of application show that a change in design (2.7 x 2.7 square mesh to 2.2 x 2.5 triangular mesh) reduces P80 by 65%, from 17 to 6 inches, approximately. Additionally, the results show that greater operational efficiency was achieved by increasing excavator productivity by approximately 15.6%.

El presente trabajo de investigación está orientado a la mejora de la fragmentación de rocas de la zona de Machu Picchu, la misma que se encuentra en el tajo Santa rosa de la Empresa Administradora Cerro S.A.C. Mediante el diseño de la malla de perforación, se considera la modificación de los parámetros como longitud y diámetro de taladro, así mismo con la aplicación de la nueva tecnología plasma. Se usó esta innovadora opción por tener como limitación la cercanía de zona urbana a unos 120 metros aproximadamente del proyecto. Aunque esta nueva opción permitía cumplir con la norma, no logró ser idóneo por los resultados en la fragmentación del macizo rocoso, generando un 64% de bancos mayores de 18''. Con este indicador se debió usar equipos adicionales generando un aumento en los costos operativos. Por consiguiente, se desarrollaron diversas pruebas con las mallas de perforación, y con la distribución de carga, considerando el tipo del macizo rocoso del proyecto, siendo Regular B, con RMR 49. Al finalizar el análisis de esta información se diseñó la propuesta de solución que consistió en la modificación de los parámetros de la malla de perforación, adecuados como el burden, espaciamiento, y altura de los taladros de producción. En el desarrollo del presente trabajo se tuvo resultados favorables en la disminución del tamaño de las rocas obtenidas después del disparo. / This research work aimed at improving rock fragmentation in the Machu Picchu area, the same one that found in the Santa Rosa Tagus of Empresa Administradora Cerro S.A.C. Through the design of the perforation mesh, consideration and modification of the parameters such as length and diameter of the hole, applying the new plasma technology. This innovative option used because it limited by the proximity of an urban area approximately 120 meters from the project. Although this new option allowed us to comply with the standard, it was not suitable due to the results in the fragmentation of the rocky massif, generating 64 % of banks larger than 18". With this indicator, additional equipment had to used, generating an increase in operating costs. Consequently, various tests developed with the drilling meshes and with the load distribution, considering the type of the rocky massif of the project, being Regular B, with RMR 49. At the end analysis of this information, the solution proposal was designed which consisted of modifying the parameters of the drilling mesh, suitable as the burden, spacing, and height of the production holes. In the development of the present work, favorable results were obtained in the reduction of the size of the rocks obtained after the shot. / Tesis