Aquathermal effect of anomalous pressure generation in consolidating minefill

Abstract

Recycling cement-amended tailings into subsurface cavities has delivered competitive socioeconomic revenue for underground mining. However, recent instances of anomalous thermal pressure in consolidating backfill have raised growing concerns over the current design philosophy. This study demonstrates that the excellent hydraulic sealing and considerable chemical energy inherent in cemented backfill can spontaneously generate substantial thermal pressurization through constrained pore-fluid expansion. An analytical solution is hence developed for characterizing the non-isothermal behaviour of hydrating backfill based on classical thermo-poroelasticity. The influence of preparation condition and mix design on the pressure evolution in time domain and during spontaneous heat generation is then thoroughly examined, successfully pinpointing the causal mechanism responsible for typical thermal pressure anomalies. It is demonstrated that the anomalous pressure is attributable to both the conservative binder usage, which increases the intrinsic heat load, and the elevated initial temperature, which promotes water volume expansion. The fundamental influence of temperature-sensitive water expansivity on the path dependence of thermal pressurization is also elucidated. This study thus contributes to a comprehensive understanding of the thermally correlated pressure anomalies that frequently occur in field operations. These critical findings would also hold practical implications for designing successful backfill solutions in challenging mine environments.