Comprehensive monitoring for rockburst at a pumped storage power station in northeast China

Abstract

Rockburst is characterised by the wide occurrence areas and the long delayed time at a pumped storage power station in Heilongjiang province of China. For the study, a new method is proposed to identify the induced rockburst based on the combination of microseismic (MS) and electromagnetic radiation (EMR) monitoring methods. EMR monitoring method is introduced to make up for the shortcomings of the monitoring blind area caused by the propagation path of wave velocity during MS monitoring and a beneficial attempt is carried out for the comprehensive application of the two methods to monitor the rockburst. Firstly, a MS monitoring system is established around the underground powerhouse to recognize the propagation of micro-fracture during the deep excavation, while the typical five parameters including the frequency of the microseismic events, the total energy of daily events, energy index (EI), cumulative apparent volume (CAV) and microseismic signal b-value are analyzed to reveal the temporal and spatial evolution law of microseismic events. Secondly, an EMR monitoring system is also established near the MS events clusting area to study the characteristics of EMR produced from the fractured rock mass. The temporal and spatial variation of the two parameters including electromagnetic radiation intensity and pulse number are also analyzed and the distribution of higher values are compared with the geological structure. Finally, the correlation of electromagnetic signals, microseismic signals and local stress is studied based on theories of geophysics, electromagnetism and rock mechanics, and some credible results are obtained. Here are the following resluts: (1) The microseismic events are characterized by spatial clustering, and the joint action of the excavation disturbance and the weak structure body of the surrounding rock mass are the main factors for rockburst. The trend of sharp decrease of energy index and sudden increase of cumulative apparent volume generally indicates the occurrence of rockburst or macro-fracture. The magnitude of b value indicates that the rockburst failure type in the project belongs to fracture-slip rockburst. (2) The sudden change of electromagnetic radiation intensity in the fault fracture zone of the underground powerhouse can be used as the precursor information of rockburst or large-scale rupture events.(3) The micro-fracture activities revealed by EMR and MS methods are consistent in spatial distribution. The distribution of the peak values of electromagnetic radiation pulse number are basically consistent with the direction of the apparent stress migration disturbed by the field construction situation. So we can infer that it will play an important role to improve the accuracy of rockburst prediction based on the analysis of the multi-source singals.