Estimation of pore fluid pH effect on Skempton’s pore pressure parameter Bw
Debnath Mondal, Debasis Roy, Saswati Ghatak
In the proceedings of: GeoVirtual 2020: 73rd Canadian Geotechnical ConferenceABSTRACT: Since near-surface aerobic biologic processes produce CO2, the amount of biogenic CO2 is expected to influence pore fluid compressibility. Consequently, pore water pressure development during events that deform a soil mass that holds microorganisms that produce CO2 rapidly is also expected to depend on CO2 production, as will be the liquefaction susceptibility of such soils. However, bacterial metabolic processes, life cycle, and CO2 production affect pore fluid pH as well. That, in turn, would affect CO2 solubility. The relationship between Skempton’s pore water pressure parameter, Bw – the ratio of pore water pressure rise during rapid deformation of soil mass to the corresponding incremental mean normal stress – and the amount of CO2 production is expected to be pH-dependent. A pH-dependent relationship between Bw and CO2 amount has been derived here from theoretical considerations. The relationship was validated against the data from a series of closed-system laboratory experiments on loose sand that hosted two species of aerobic soil bacteria, Lysinibacillus sp. (DRG3) and Bacillus megaterium (RB-05). These species were minimally sustained within pore space in such a manner that one of three distinct metabolic pathways was triggered; one involving the production of exocellular metabolic substances (EPS), while the other two involving the production of EPS and calcite in the presence and absence of urea. Amounts of CO2, pH, and the corresponding values of Bw were tracked over up to 72 hours for these cases. Bw estimates from the theoretical relationship derived herein were found to agree reasonably with experimentally obtained values.
RÉSUMÉ: Puisque les processus biologiques aérobies en surface peuvent produire du CO2, on s’attend à ce que la quantité de CO2 biogénique influence la compressibilité des fluides poreux. Par conséquent, le développement de la pression de l’eau des pores lors d’événements qui déforment une masse de sol qui contient rapidement des micro-organismes qui produisent rapidement du CO2 devrait dépendre de la production de CO2, tout comme la susceptibilité à la liquéfaction de ces sols. Cependant, les processus métaboliques bactériens, le cycle de vie et la production de CO2 affectent également le pH des fluides pores. Cela affecterait à son tour la solubilité du CO2. La relation entre le paramètre de pression de l’eau des pores de Skempton, Bw – le rapport de l’augmentation de la pression de l’eau des pores lors de la déformation rapide de la masse du sol au stress normal moyen progressif correspondant – et la quantité de production de CO2 devrait être dépendante du pH. Une relation dépendante du pH entre la quantité de Bw et de CO2 a été dérivée ici de considérations théoriques. La relation a été validée par rapport aux données d’une série d’expériences de laboratoire à système fermé.
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Mondal, Debnath, Roy, Debasis, Ghatak, Saswati (2020) Estimation of pore fluid pH effect on Skempton’s pore pressure parameter Bw in GEO2020. Ottawa, Ontario: Canadian Geotechnical Society.
@article{Mondal_GEO2020_256,
author = {Mondal, Debnath}, {Roy, Debasis}, {Ghatak, Saswati},
title = Estimation of pore fluid pH effect on Skempton’s pore pressure parameter Bw ,
year = 2020
}
title = Estimation of pore fluid pH effect on Skempton’s pore pressure parameter Bw ,
year = 2020
}