Authors: Belem, T; Mbonimpa, M; Oke, J; Gélinas, LP

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Belem, T, Mbonimpa, M, Oke, J & Gélinas, LP 2023, 'Assessment of static liquefaction susceptibility of early age cemented paste backfills', in GW Wilson, NA Beier, DC Sego, AB Fourie & D Reid (eds), Paste 2023: Proceedings of the 25th International Conference on Paste, Thickened and Filtered Tailings, University of Alberta, Edmonton, and Australian Centre for Geomechanics, Perth, pp. 154-169,

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The use of cemented paste backfills (CPB) for stope filling as a tailings management method becomes almost indispensable for flexible, selective and safe underground mining operations. For CPB to play the role of secondary ground support, it must develop a certain uniaxial compressive strength (UCS). The UCS value is almost linearly proportional to the binder content used. However, the cost of the binder represents 8 to 16% of the operating costs of mining with cemented backfill. That is the reason why mining companies seek to reduce the binder cost by reducing the amount of binder in the CPB mixtures. Unfortunately, a reduction in the binder content could cause a significant decrease in CPB strength, particularly at early ages. Such a CPB strength reduction, under undrained conditions, may cause liquefaction-induced failures at early ages due to seismic shaking or static loading. Static liquefaction can occur if the CPB show contractive behaviour during undrained loading and if there is a triggering mechanism present. The triggering mechanism can be due to a rapid rate of CPB raising (overloading), changes in porewater pressure or reduction in lateral confinement. The objective of this study is to experimentally assess the static liquefaction susceptibility of CPB containing low percentages of HS Portland cement (1.5, 1.75 and 2 wt%) at early ages (3 and 7 days). For each cement percentage and both curing times, isotropically consolidated undrained (CIU) triaxial compression tests were performed. Preliminary results are provided and the conditions for static liquefaction triggering are either null effective minor stress or when the pore pressure ratio (ru) reaches or is close to unity (ru = u/’3 = 1). The results showed that only the CPB studied using 1.5 wt% cement reached the condition of initial static liquefaction temporarily (axial strain in the range 0.5–3.5%) before resisting against liquefaction development (dilative behaviour).

Keywords: static liquefaction, cemented paste backfill (CPB), unconfined compressive strength (UCS), consolidated undrained triaxial, contractive behaviour

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