Numerical modelling of thermally and hydraulically coupled processes in hydrating cemented tailings backfill columns

Abstract

A coupled thermo-hydro-chemical (THC) model has been developed to study the thermally and hydraulically coupled processes in hydrating cemented paste backfill (CPB). Afterwards, the THC model is validated against laboratory data (CPB made of Portland cement and CPB that contains mineral admixtures) and field CPB column studies (CPB cured in underground mine environments). In addition, the validated THC model is applied to simulate and predict the thermal (e.g. temperature development and thermal conductivity), hydraulic (e.g. water drainage, suction or negative pore-water pressure development and hydraulic conductivity) and physical (porosity) evolutions of the CPB columns under different conditions, such as various CPB temperatures and water-to-binder ratios. The presented outcomes can contribute to a better understanding of the coupled thermal-hydraulic processes that occur in CPB and the thermal and hydraulic behaviours of CPB structures, as well as a better design of stable, durable and cost-effective CPB mixtures. IntroductionThe technology of cemented paste backfill (CPB, a mixture of binders, water and tailings) [1-5] is widely used in underground mining practices all around the world [6][7][8][9][10][11][12]. The utilisation of CPB technology not only allows a significant reduction in the cost and environmental issues associated with surface tailings storage facilities (e.g. tailings dams), but also provides a safe working environment for miners by supporting the surrounding ore body and rock [13][14][15][16].Mechanical stability, environmental and durability properties, as well as thermal properties, are important performance characteristics of CPB structures [17][18][19]. Once placed into underground openings, CPB structures should bear enough strength or show acceptable mechanical stability to support adjacent stopes during mining operations, and thereby ensure the safety of the mine workers. The uniaxial compressive strength (UCS) is the most common parameter used to evaluate the stability of CPB structures in practice. However, the strength (UCS and shear strength) and effective stress development within the CPB are strongly affected by the thermal (e.g. heat induced by the binder hydration) and hydraulic (e.g. positive pore-water pressure, negative pore-water pressure or suction) processes that occur within the CPB and their interactions

Transportability and pressure drop of fresh cemented coal gangue-fly ash backfill (CGFB) slurry in pipe loop

“…According to the data in Table 1 the chemical reaction (i.e., cement hydration) contributes to the generation of ettringite and C-S-H [23][24][25]. These hydration products that have cementing properties precipitate among the coal gangue particles and integrate them together.…”

A coupled thermo–hydro-mechanical–chemical model for underground cemented tailings backfill

“…The temperature can further affect CPB properties in binder hydration, such as the strength , microstructure, saturated hydraulic conductivity ) and self-desiccation intensity and rate (Wu et al, 2013); (ii) thermal gradients can lead to mechanical deformation through thermal expansion or contraction; and (iii) the temperature level is also a significant influencing factor in the surface evaporation rate (Ghirian and Fall, 2013a).…”

“…A thermo-chemo-mechanical (TCM) model (Fall and Nasir, 2009) was proposed to simulate the response of CPB under thermal loading conditions. In order to describe the coupled thermal and hydraulic processes within CPB, a thermo-hydro-chemical (THC) model was developed (Wu et al, 2013). A hydro-chemo-mechanical (HCM) model which couples cement hydration with conventional consolidation analysis was presented by Helinski et al (2007).…”

A coupled chemo‐viscoplastic cap model for simulating the behavior of hydrating cemented tailings backfill under blast loading

“…In order to quantify the evolution of the binder hydration process, as mentioned earlier, the equation for the degree of binder hydration proposed by Schindler and Schindler and Folliard for cementitious materials is adopted. This equation has been successfully applied to predict the progress of binder hydration for CPB (e.g., Wu et al ), and is expressed as where ξ is the degree of binder hydration that represents the fraction of the binder that has reacted at an equivalent age t e , τ is the hydration time parameter at the current temperature of the cement‐based material, β is the hydration shape parameter, and ξ u the ultimate degree of binder hydration, which depends only on the water‐binder ratio ( w / c ) and has been modified by Wu et al as …”