Consolidation and dynamic response of a layered mine tailings deposit in centrifuge tests

Tailings from a mining project located in a seismically active region were used to construct and test a layered deposit on the geotechnical centrifuge at the Center for Earthquake Engineering Simulation (CEES) at Rensselaer Polytechnic Institute (RPI). A set of six centrifuge tests was conducted to evaluate consolidation rate, settlement accumulation, shear strength evolution, and response to seismic loading. The material was liquid at disposal, so instrumentation of every layer proved to be a challenge. A total height of about 30 m of mine tailings was deposited in prototype scale (80 g). Brief consolidation of each layer took place at a lower centrifugal acceleration, thus enabling the material to gain some strength and facilitating instrumentation, while simultaneously modeling a few days between disposal of subsequent layers. Miniature pore pressure transducers were used to measure water pressure and settlement, bender elements for shear wave velocity, linear variable differential transformers (LVDTs) for displacement, and miniature accelerometers for dynamic loading. The complete deposit consolidated at 80 g for more than two years in prototype scale, but most settlement, excess pore pressure dissipation, and stiffness increase occurred within the first 0.5 years. A mild slope was excavated at the surface after consolidation and the deposit was then subjected to a moderately strong harmonic motion consisting of 50 cycles. Signs of liquefaction were detected in the pore pressure, acceleration and lateral displacement readings up to mid-depth, and the slope was somewhat flattened after dynamic loading.