Overall and bench slopes stability study using microseismic monitoring technique at Sandaozhuang open pit mine

摘要

The Sandaozhuang open pit surface mine is a large molybdenum and tungsten mine, the geological reserves, of which, ranks it the highest in Asia and third in the world. Underground mining commenced in the 1960s, when the orebody was exploited without proper strategy. Open pit mining, owned by the China Molybdenum Co. Ltd, commenced in 2002, with current production capacity of 50,000t/d. A huge volume of known and unknown old underground workings exist under the overall and bench slope from early underground mining. The open voids are "1,200,000 m~2 in area and ~18,000,000 m~3 in volume, according to the available data. The mined out areas seriously affected the safety of equipment and personnel, and several bench and inter-bench slopes collapses have occurred over the years. Therefore, a 48-channel microseismic monitoring system was established in 2012, to carry out real-time monitoring of the slope stability. This study was to acquire rock mass wave velocity, attenuation coefficient and the Q-values through field testing of the characteristics of stress wave propagation in mined-out area and fractured rock masses. The testing results provided the basic parameters for sensor layout, source location optimisation and quantitative stability analysis of rock mass etc. By establishing a quantitative relationship between the peak particle velocity (PPV), the moment magnitude and the distance to source, the PPV value was calculated to assess the effect of blasting vibration on the stability of slope and underground mined out areas. The aggregation degree of localised microseismic events, the b value, and the energy index and apparent volume value were used to quantitative stability assessment of overall and bench slopes. At present, the microseismic monitoring technology has become an indispensable method in ground movement monitoring and geotechnical hazard management at the Sandaozhuang open pit mine.