H. Reginald Hardy

Study of microseismic activity associated with a longwall coal mining operation using a near-surface array

Abstract Microseismic studies associated with a longwall coal mining operation are described. The mine under study was located some 600 ft. below surface. Seismic events associated with controlled roof failure, and with stress development in both the roof and adjacent pillars were monitored by a seven-station near-surface array. The studies were carried out over a 6-month period during which the longwall face moved horizontally some 800 ft. below the area defined by the seismic array. Brief details are presented of the mobile monitoring system and the analysis techniques employed. Typical results obtained during the study are discussed along with suggestions for improving future studies of this type.

Laboratory study of acoustic emission and particle size distribution during rotary cutting

Abstract Studies have been under way by the authors to investigate the character of the bit-coal interaction during coal cutting and its influence on the size and shape distributions of the generated dust. An important aspect of these studies is the use of acoustic emission (AE) and associated artificial intelligence techniques for remote monitoring of coal cutting operations. Recent papers by the authors have provided a general outline of the overall study, and the preliminary results of linear, single-bit cutting (Hardy, Shen 1996, Shen, Hardy 1996, Hardy, Shen 1995). The present paper will focus on the test facilities, experimental techniques, and results associated with the rotary, single-bit cutting studies. These results indicate that the relationship of particle size characteristics to cutting parameters was more obvious than in the linear, single-bit studies. It was observed that the higher advance rate (0.05 in./cut) results in a lower fine dust percentage, a higher all-particle Gaudin-Schuhmann slope, and a higher amount of overall coal particles than the lower advance rate (0.025 in./cut). The correlation of AE signal characteristics with the coal cutting data was investigated using ICEPAK, a commercially available artificial intelligence package developed by Tektrend International Inc. In the current rotary cutting study it was found that more features were needed to build a suitable classifier than in the case of the linear cutting studies presented earlier (Shen, Hardy 1996); however, acceptable recognition rates were obtained in most cases. An associated neural network method was also applied, and the results were compared with those from conventional methods. It is found that, although the neural network method does increase the recognition rates, analysis time is considerably increased.

Geotechnical field applications of AE/MS techniques at the Pennsylvania State University: a historical review

Abstract Since the early 1970s there has been an accelerating interest in the use of acoustic emission/microseismic (AE/MS) techniques for the laboratory and field investigation of geological materials and structures. Basic AE/MS research and the application of AE/MS techniques to a variety of geotechnical problems has been under way in the Penn State Rock Mechanics Laboratory since 1965. To date, studies have involved a wide variety of field topics, including: cavern stability, stability of natural gas storage reservoirs, strata control in longwall coal mines, rock bolt stability monitoring, effects of blasting, mine and tunnel roof stability, subsidence monitoring and rock slope stability evaluation. This paper reviews the development of AE/MS research at Penn State, describes briefly a number of the major field studies undertaken, and discusses on-going and future research programmes.

Microseismic Techniques — Basic and Applied Research

Microseismic Techniques — Basic and Applied Research. The phenomenon of microseismic activity appears to provide the basis for one of the most useful tools presently available in the field of rock mechanics. During the last six years the Rock Mechanics Laboratory at The Pennsylvania State University has been involved in studies related to this phenomenon, and the present paper describes a number of the basic and applied research studies undertaken. Emphasis however will be on the applied aspects of these studies, including the use of microseismic activity in the laboratory to define failure in pressurized gas storage reservoir models, and in the field to study underground gas storage reservoir stability and to evaluate coal mine strata control techniques. A mobile laboratory has been under development in conjunction with the two field programs and a brief description of this laboratory is included.