Scholarly record

QUANTIFYING CO2-INDUCED EXCESS PORE PRESSURE IN SATURATED MINE WASTE: SEQUENTIAL REACTIVE TRANSPORT AND TWO-PHASE FLOW MODEL

Donata Wardani

Abstract

A recent experimental study identified a novel "hydro-chemo-mechanical" trigger for soil liquefaction: internal pore-pressure build-up generated by carbon dioxide (CO2) accumulation during the buffering of acidic mine water by carbonate-rich soil. However, the interpretations of the experiment were constrained by heterogeneity and the underestimation of pressure build-up due to system failure following the peak pressure. This study addresses these limitations by developing a numerical framework to quantify the transition from chemical reaction to physical overpressure in saturated mine waste. Based on the experimental setup of Wardani et al. (2025), we employ a 1D reactive transport model (RTM) under local equilibrium assumptions to simulate neutralisation by carbonate minerals. The resulting gas generation rates are then used as source terms in the OpenGeoSys (OGS) Hydro – Two-Phase – Mechanical (H2M) module to predict gas pressure and the corresponding liquid pressure. Simultaneously, H2M simulations are conducted using different source term configurations: (1) measured free CO2 gas discharged, (2) combined measured free gas and dissolved CO2, (3) measured free gas coupled with dissolved CO2 calculated via PHREEQC. While data collection is ongoing, preliminary findings demonstrate higher gas and liquid pressures when dissolved CO2 is considered. This confirms that the accumulation of dissolved CO2 is a primary contributor to pressure peaks in rigid, saturated systems, where the addition of highly compressible CO2 mass into the aqueous phase increases the total pore pressure even in the absence of a distinct gas phase. Furthermore, the H2M models incorporate different material properties in each setup, accounting for the heterogeneity inherent in mine waste. This framework provides a robust predictive tool for assessing the "inner initiation" of liquefaction in lignite overburden dumps, specifically as a function of CO2-induced excess pore pressure. The final results will be presented in the full-text paper and at the conference.

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