Microseismic monitoring of highwall mining stability at Moura Mine, Australia (original) (raw)
Related papers
2000
Experiments carried out in a working iron mine validated the microseismic monitoring technique as a means of detecting fracture noise emissions regarded as signals indicating an incipient collapse. In the experiment surface recordings were made of the microseismic signals corresponding to fractures and local collapse phenomena generated at the mine bottom by deliberately destroying pillars. The pillar removal operations and the collapse of the roof were systematically correlated with a series of microseismic events. The experiment served to validate the microseismic monitoring technique as a means of detecting surface precursors of a collapse, to demonstrate the effectiveness of the technique, and to calibrate the principal parameters of a microseismic monitoring System adapted to detection and monitoring in areas where there is a risk of collapse.
Advance detection of Slope Failures in Opencast Coal Mines using Microseismic technology
The application of microseismic monitoring in opencast coal mines provides an ideal method for the analysis of slope status. Since slope angles are critical to the economics of open pit mining, microseismic monitoring of fracturing within a slope can add significant knowledge to assess the status of slopes in terms of stability. An advanced high dynamic range microseismic instrumentation with latest computer methods/analysis will help to investigate strata behavior in real time. In the present study, an array of high frequency 15 Hz triaxial geophones were installed in boreholes in Opencast Coal Mine in highwall as well as dumps for monitoring the slope movements. The microseismic energy generated due to rock movements is continuously recorded by these geophones. The recorded events are stored in seismic recorder. The stored data will be transferred into a data acquisition and processing system via wireless repeater station. The data recorded are later processed for their origin of ...
Microseismic tools for the analysis of the interaction between open pit and underground developments
The transition from surface to underground mining presents a series of technical and operational challenges, in particular those arising from the interaction between the cave and the overlying pit. Seismic monitoring provides a unique means to obtain near real-time information about the development of the fracturing process induced by the mining operations. This paper presents the analysis of temporal, spatial and source size patterns in the seismicity recorded during undercutting and production at the Palabora Mine leading to slope failure in the open pit above, and relates these results to full-scale analysis of the rock mass behaviour in three-dimensional numerical models. Based on the application of the techniques described herein, it is shown that the back analysis of the seismic data provides a prediction technique that could now be employed during the planning stages of a mining operation. It is hoped that by employing these new techniques it would be possible to incorporate results from predicted fracture network behaviour into engineering designs in similar future mining operations and thus provide a means to predict and mitigate against large scale failure as observed at the Palabora Mine.
Interpretation of microseismic effects from response to large coal mine blasts
Earthquake Resistant Engineering Structures VIII, 2011
Response of a residential structure to ground motions generated by large, surface coal mine blasts can provide information regarding the cracking severity of microseismic events. Microseismic events produced by small earthquakes, mine-collapse and reservoir induced seismicity, etc. can lead to concern on the part of those who feel the ground motion. These concerns can be addressed by reference to low frequency blast generated ground motions that have not caused cracking. This paper presents measured response of a structure to motions producing peak particle velocities of 10 to 19 mm/s and ground displacements of 0.3 mm at 5 to 15 Hz, which can be employed to interpret microseismic phenomena of any sort. Measured responses include velocity responses of the superstructure and midwall as well as vibratory response of existing cracks in walls. Response spectra of these blast generated motions are compared to those generated by moment magnitude five midcontinent earthquakes to determine the relative impact. The structure was inspected for crack extension after each blast and none were found
International Journal of Rock Mechanics and Mining Sciences, 2019
A highly-stressed shaft pillar is prone to large seismic events, falls of ground and rockbursts, which may cause injuries and loss of production, especially in weak geotechnical zones. It is thus important to identify weak geotechnical zones in order to mitigate risks. In this study, we present integrated studies (underground mapping, petrology, rock mechanics and high-resolution microseismicity analysis) to understand the different geotechnical zones in the shaft pillar of Cooke 4 mine in South Africa. The footwall of the remnant shaft pillar comprises the Upper Elsburg reef of the Mondeor Formation, while the Ventersdorp Contact Reef (VCR) of the Venterspost Formation and soft/weak lavas of the Westonaria Formation form the hangingwall. Results from underground mapping and microscopic analysis show that the shaft pillar is composed of quartzites, pebbly quartzites, argillaceous quartzites and conglomerates. Underground mapping further shows that the shaft pillar is characterized by several discontinuities, which vary from minor to macro scale fractures. Laboratory uniaxial compressive strength (UCS) tests indicate that quartzite has the strongest strength, followed by pebbly quartzite, argillaceous quartzite and lastly, conglomerate. Analysis of high-resolution acoustic emissions (AEs) clusters indicates that the majority of AEs are associated with the mining stope faces. The clusters show the formation of Ortlepp shears ahead of the stope, which is caused by the excavation-induced stress field. Microseismic data further reveal that the fracture turning-point occurs in the soft strata (weak hangingwall lavas). The integration of these datasets has allowed us to develop the fracture model for different geotechnical zones, which concurs with previous models developed for the similar underground environment (i.e., weak/soft lava hangingwall and quartzite/conglomerate footwall). This has major implications for future mining, support, production and safety.
Microseismic data — a comparison between routine trigger method and continuous data processing
Over the years there have been several attempts to undertake routine real-time microseismic monitoring of open pit mine slopes. This technique has been commonly used in underground operations to manage induced seismicity and rockburst. However, the microseismic monitoring in open pits is still experimental and further studies are required. In this paper, we analysed the data from MMG Century mine where, in November 2013, a microseismic system was installed in order to monitor a large scale unstable slope. Design of the system and installation of the instruments were performed by the Institute of Mine Seismology. The seismic events were recorded, based both on a triggered scheme and in continuous mode. As part of our research project, data was given to four independent groups to be analysed and provide their own results. One group applied a routine method using the triggered data, manually processed them and made them available for the engineers on site within 10 minutes. The other three groups later reanalysed the data using both triggered and continuous waveform. Our work compared the different results obtained, and highlighted some of the key points engineers should be aware of in the design and implementation of a microseismic system in open pit mines.
Routine Micro-Seismic Monitoring in Mines
Routine seismic monitoring in mines enables the quantification of exposure to seismicity and provides a logistical tool to guide the effort into the prevention and control of, and alerts to, potential rock mass instabilities that could result in rock bursts. One can define the fol-lowing five specific objectives of monitoring the seismic response of the rock mass to mining: rescue of personnel, prevention, seismic hazard rating, alerts -including short term response to unexpected strong changes in certain parameters -and back analysis to improve the efficiency of both the mine layout design and the monitoring pro-cess. A quantitative description of seismic events and of seismicity are necessary, but not sufficient, in achieving the above objectives. The paper describes the basis of a modern digital seismic technol-ogy and seismological parameters used to quantify seismic sources and seismicity for seismic hazard assessment and rock mass stability analysis.
The application of a routine high resolution microseismic monitoring system installed in an opencast coal mine for monitoring highwall slope failures is discussed. A PC based microseismic network consisting of geophones, data loggers, GPS synchronization and Ethernet antennas for wireless communication is employed to study the impact of induced seismicity on the slope failures in real time. The study aimed to understand the rock mass response to mining induced seismicity from the behavior of seismic events within rock mass. The level of induced seismicity due to underground excavation is determined from the seismic source parameters such as locations, magnitude, and seismic energy. The status of the slope is assessed by the quantification of the microseismic events. The understanding of spatial and temporal distribution of the seismic events within the mining district correlated well with the existing geological structures and the excavation sequence. The application of microseismic system in the opencast mine has not only yielded confident results, but also marked as an effective tool for continuous monitoring of seismicity on the deep opencast slopes for mitigating the seismic risks and hazard management.