Mining Induced Ground Motions in a Tailings Dam

Abstract

Mining induced seismicity can expose tailings dams to ground motions with potential to trigger a failure, if the structure reaches a certain level of vibrations that could exceed the seismic coefficient design criteria from pseudostatic analysis. Despite the cited risk, mainly for dams that are closer to open pits, few dams in Brazil are monitored by microseismic systems, and there are no references in the literature about continuous seismic monitoring both in open pit (source) and tailings dam, which represents the motivation of this paper. A microseismic system was commissioned in Cajati Mine, São Paulo, to record seismic events continuously in an array of 16 geophones (14 Hz and 4.5 Hz), installed in boreholes near the open pit (12 sensors) and in the dam (4 sensors), has measured values of PGA (Peak Ground Acceleration) and PGV (Peak Ground Velocity) related to 2,972 induced events from rock removal in the open pit. During the period monitored, the total of 109 events have triggered sensors in both structures, producing 920 seismograms, with the highest values of PGA and PGV of 0.0135 m/s2 (0.1358% of g) and 0.0892 mm/s. The highest PGA value is 36 times lower than the vertical coefficient of 3% of g defined by Brazilian technical standard to dam design criteria, normally used in common pseudostatic analysis from geotechnical engineers. A routine microseismic monitoring brings a new set of valuable actionable data and information to support the management of geotechnical tailings dams’ risks, under the conditions of vibrations induced by mining production.