This thesis investigates microseismic P-wave arrival time detection performance of automatic picking algorithms, as well as the handpicking performance of human experts. The data set used in this project was collected from Malmberget mine (LKAB, Sweden) and the handpicked P-wave arrivals were prepared by multiple expert analysts from the Institute of Mine Seismology (IMS). Characterization of the event records in the data set was completed including the magnitude distribution of the events, noise content of the traces, and frequency spectrum of the traces. Three promising automatic P-wave picking algorithms from previous seismological research were investigated: the short-term average to long-term average ratio detector (STA/LTA), the characteristic function detector (CF), and the autoregressive modelling detector (ARfpe). Several versions of each algorithm were implemented, and the most promising versions were tested on the full dataset of microseismic events. The STA/LTA algorithm and CF algorithm were superior to the ARfpe algorithm in terms of accuracy and percentage of false negatives (missed P-wave arrival time picks). The analyst P-wave arrival times were compared and statistical distributions of the analyst P-wave arrival time differences were studied. The analyst P-wave arrival time difference and algorithm P-wave arrival time difference were defined as the mean analyst P-wave arrival time minus the specific analyst P-wave arrival time pick or the specific algorithm P-wave arrival time pick. The analyst and algorithm P-wave arrival time differences were combined into separate statistical distributions and compared. The analyst P-wave arrival time distribution lengths varied by a factor of 5, and the percentage of outliers in the distribution varied between 12% and 32%. The STA/LTA algorithm had comparable distribution statistics to the worst analyst P-wave arrival in terms of median value, distribution length, and percentage of outliers. However when the number of traces with automatic P-wave picks within the analyst handpicking range was calculated the STA/LTA algorithm had only 32.0% of picks and the CF algorithm had only 11.6% of picks. / Thesis (Master, Mining Engineering) -- Queen's University, 2014-04-30 21:45:13.741

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Surface seismic techniques lack the resolution to image the top 100m or so of the earth's surface necessary for opencast coal exploration. The work reported in this thesis is the development of borehole seismic methods making use of the closely spaced boreholes that are routinely drilled by British Coal. The first method investigated was to use a tomographic technique to observe any reduction in seismic velocities above old workings, and hence infer the presence of old workings. In order to obtain clear images of the subsurface, it was necessary to interpret the field data for the presence of head waves, and to pick the later arrival direct waves for the tomographic inversions. However, independent data obtained from uphole surveys showed that there was no measurable reduction in the seismic velocity above old workings for strata below the water table, and the tomographic method was abandoned in favour of borehole seismic reflection methods. Fifteen hole-to-surface seismic reflection surveys were acquired using down- hole explosive charges as sources and a linear spread of surface geophones passing through the borehole position as receivers. A complete package of processing software was developed for processing the data, and eight of the surveys are presented in this thesis. The final migrated and stacked sections delineate a washout and faulting at both large and small scales. The vertical resolution of the data is high due to the wideband temporal frequencies in the data, typically up to 300Hz.The hole-to-surface method is compared to the crosshole seismic reflection method, which was developed in parallel by M. J. Findlay. The relative merits of the two techniques are discussed, and suggestions are made to improve the acquisition of the data to make both methods applicable to a wider variety of problems. Although the vertical resolution of the hole-to-surface method is lower than the crosshole method, this could be more than compensated for by extending the hole- to-surface method to three-dimensions, using areal arrays of surface geophones around the borehole.

Colliery tailings are laminated sediments which vary from coal-rich horizons of coarse sand size, to fine silt horizons composed mainly of quartz, illite and kaolinite. The proportion of finer laminae increases away from the inlet of the containing lagoon, although both fine and coarse bands are found everywhere in the lagoon. Coal itself has a low specific gravity and high friction coefficient. The density increases and the shear strength decreases away from the inlet. Both the average coal content (47%) and friction angle (35º) are higher for tailings than for coarse colliery discard (14% and 31º respectively). The permeability of the contrasting laminae differs greatly, and consolidation and drainage in lagoons is therefore dominated by the horizontally laminated structure. Much of the water in lagoons drains laterally to the embankments. This water contains dissolved solids which reflect the groundwater chemistry of the Coal Measures at depth, being both saline and rich in sulphates. Overtipping lagoons with coarse discard is being used increasingly for waste disposal purposes. It is possible to overtip with a 1.5m high layer of discard using a D6 vehicle at a sediment shear strength of 3 KN/m(_2) . However, to include a safety margin, 4.5 KN/m(_2) should be the lower bound. An effective stress stability study of overtipping indicates that a desiccated surface is necessary; the operation cannot progress where supernatant water remains on the lagoon. In terms of liquefaction hazards, vehicle vibration levels are not high enough to be of concern. Similarly, measured ground vibrations produced by explosives did not liquefy a lagoon being overtipped. It is suggested that a 200-year return period earthquake will not cause problems in this respect.

This thesis is concerned with the development of the cross-hole seismic reflection surveying method with particular application to the shallow Coal Measures strata found in opencast coal mining prospects in the U.K.A field acquisition technique developed for shallow boreholes utilising explosive sources and hydrophone receivers is described. Data have been acquired from several test sites in northern England. Data-processing techniques including wavefield separation and waveshaping deconvolution have been developed for cross-hole data and the theories behind these techniques are discussed. Methods of imaging cross-hole reflection data including the 'VSP-CDF transformation and Generalised Kirchhoff migration are applied to computer- generated synthetic data and to real data in order to yield a depth section of the seismic reflectivity between the boreholes. Finally, the data-processing and imaging techniques developed are applied to real data acquired at British Coal Opencast exploration sites in northern England between 1987 and 1990.

The present study was undertaken to investigate the mechanism of void migration and the collapse characteristics of old shallow surface (< 50m), pillar and stall coal mine workings. Simple stereo-photographic techniques have been employed to record these structures where they occur in the high walls of NCB and private opencast coal sites. Several relationships have been identified from this data, and the investigation concludes that the crushing of coal pillars at depth is rare and that the principal mechanism of failure involves the collapse of the roof material into the working. A classification of failure mechanisms based on the frequency and spacing of horizontal and vertical discontinuities relative to the span of the working is proposed. Two distinct situations for analysis are recognised. The first involves the stability of the immediate roof, while the second is concerned with the stability of the 'arch' that develops when the immediate roof beam collapses. Continuous roof beams have been found to be rare in Coal Measures rocks and therefore simple beam analysis is considered to be of little use. Where discontinuities are present Voussoir beam analysis may be appropriate, and Voussoir beam theory has been corrected and extended to overcome some of the problems recognised with the technique. Bulking and arching have been recognised as the 'normal' limiting factors on the height of collapse and are considered as complimentary failure mechanisms. For a 'typical coal mine collapse' situation arching is shown to be the dominant control. However, a review of arching has shown that in general all the theories underestimate the height of collapse. Thus, a statistically derived relationship of (collapse height = 2.68 X span of working) has been proposed as the limiting height for arching situations. Existing bulking relationships have been shown to be rather simplistic and appropriate corrections to the theories are suggested. An analysis of bulking factors derived from colliery discard has shown that a regional variation in this parameter is likely.

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