Date of Graduation

2003

Document Type

Dissertation/Thesis

Abstract

The underground mining industry is dependent upon the implementation of an engineering design and strategy to adequately and safely control the surrounding rock mass, with support of the roof rocks being of the greatest concern. Primary roof support systems use mechanical structures, such as roof bolts, roof trusses and cable bolts, to stiffen and control the roof rocks. Each of these systems requires the drilling of a small-diameter hole into the roof which is used to insert the mechanical structure. The structures are designed for specific geological and geotechnical characteristics and the more information that can be collected on these characteristics the greater the possibility of success for controlling the roof rocks. Roof rock characteristics are only known by the industry on a widely-spaced pattern even though most rock sequences in sedimentary basins exhibit closely-spaced facies changes which often are accompanied by significant changes in physical properties of the rock mass. These rapid changes in physical properties are often responsible for failures in the roof rocks and many times inadequate roof support strategies are applied because of this lack of knowledge. With the recent developments in microprocessor monitoring and control technologies, the monitoring of the roof drilling operation can be accomplished in a real-time and continuous basis. The data collected during the drilling operation, primarily the forces necessary to accomplish the destruction of the rocks, thrust and torque, and the velocities of the drilling operation, penetration rate and rotational velocity, can be used to provide insights into the physical characteristics of the mine roof. A research program was implemented to develop a methodology for characterizing the roof rock properties based on the drilling parameters (thrust, torque, penetration rate and rotational velocity) that are used in routine roof bolt drilling systems. The monitoring and control system was developed by J.H. Fletcher & Co. and was fitted to a twin-boom roof bolter. A series of experiments was conducted to determine the relationships between the drilling parameters and the geotechnical roof rock properties including the presence of fractures, joints and voids, the locations of rock layer boundaries and the strength of the rocks. The experiments were conducted in a laboratory and used a series of specially designed rock structures that simulated conditions found in mine roof strata. The relationships between the drilling parameters and the characteristics of interest were defined and a general model was developed that simulates the interactions between the drill bit and the rock and provides insight into the physical properties of the rocks being drilled.

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