| Abstract |
In 2006, the rate of occupational injuries and fatalities in the mining industry was 12 times higher than the national industrial average, and topped the list published by the Bureau of Labor Statistics (<a href="http://stats.bls.gov/news.release/cfoi.t02.htm"target="_blank">http://stats.bls.gov/news.release/cfoi.t02.htm</a>). Based on the same statistics, the ratio of the number of reported accidents (including both fatal and non-fatal) to the total number of employees in the mining industry is as high as 1:10. The costs associated with these accidents have placed enormous economic burdens on families and the industry, as well as on society as a whole. Indeed, the impact of occupational injuries and fatalities goes far beyond economics. Tremendous effort will be necessary to reduce the rate of occupational injuries and fatalities and to ensure mine workers' rights to "safe and healthful working conditions" (Occupational Safety and Health Act of 1970). It is of great importance that technological, managerial and regulatory aspects of the industry be fully considered in this effort. In the new century, the mining industry will be challenged to provide its working men and women with safer and more healthful working conditions. A laser-based acoustic emission (AE) detection device is proposed for work site structural stability assessment. This new device will take advantage of innovations in laser ultrasonics, artificial intelligence (AI), and advanced acoustic emission technology to provide mine workers with a unique, instant, real-time stability assessment of immediate rock structures in the working environment, which has not been attainable in the past. Nonlinear optical interfero-metry based on two-wave mixing and/or photo-induced electromotive force techniques will be used for AE signal detection from rock structures in mine sites. AI criteria will be established by wave pattern recognition to identify unstable areas in mine sites. This research will also result in a unique non-contact monitoring device for acoustic emission/microseismic studies, which will be very useful in many areas of application. If the research and development is successful, the working men and women in the mining industry will have a convenient tool to check/ monitor safety conditions at their work sites and obtain sufficient time to take action before accidents occur. The innovation will reduce occupational injuries and fatalities caused by roof falls, sidewall crumples, stope collapses, slope slides, etc. in the mining industry. The primary objective of the Phase II research is to develop the prototype of the AE detector and test it in real-world mining facilities. The primary objective consists of five major specific aims: 1. instrumentation development, 2. pre-field experiment preparation, 3. in-situ data collection, 4. AI criteria development, 5. system integration and in-situ trial. This report documents the SBIR Phase II activity entitled "A Laser-Based Device for Work Site Stability Assessment" conducted by AAC International under Grant Number 2 R44 OH007662-02 and 5 R44 OH007662-03. The project was productive and fruitful, although it has not been completed because the amount of the actual work far exceeded original estimates. Significant progress was made toward the final project goal. The concept for instrumentation of the proposed laser device for work site stability monitoring was demonstrated in the previous Phase I project. In the Phase II effort, the instrumentation was further refined into its prototype format suitable for field applications through system optimization, miniaturization, and cost reduction. A digital audio AE monitor was also developed and tested, and was the first of its kind reduced into practice in the field. AE signal detection by laser instrumentation was tested on rock materials. It was found that weak signals caused by the low optical reflectivity of rock surfaces may seriously degrade the quality of the AE detection, and effort was therefore directed toward developing an optical fiber amplifier (OFA) for compensation. In preparation for field experiments on the stability monitoring system and failure criteria development based on acoustic emission, preliminary finite element models were constructed to study stress distribution around an underground longwall stope and to simulate AE activities generated in the rock structures. This established a framework for the analytical aspects of further development for field applications. In the system integration effort, the first generation mine AE monitor implementing the proposed laser-based AE detection concept, SAFELITE-l, has been assembled with major functions tested. At this stage, one of the key components of SAFELITE-I, the optical fiber amplifier, is still under development; thus, SAFELITE-l is not yet fully prepared for field testing and failure criteria development. |
