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Preisig, Giona

Nom
Preisig, Giona
Affiliation principale
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Ancien.ne collaborateur.trice
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https://libra.unine.ch/handle/123456789/159

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  • Publication
    Métadonnées seulement
  • Publication
    Accès libre
    Regional Flow Simulation in Fractured Aquifers Using Stress-Dependent Parameters
    (2011)
    Preisig, Giona 
    ;
    Cornaton, Fabien Joel
    ;
    Perrochet, Pierre 
    A model function relating effective stress to fracture permeability is developed from Hooke's law, implemented in the tensorial form of Darcy's law, and used to evaluate discharge rates and pressure distributions at regional scales. The model takes into account elastic and statistical fracture parameters, and is able to simulate real stress-dependent permeabilities from laboratory to field studies. This modeling approach gains in phenomenology in comparison to the classical ones because the permeability tensors may vary in both strength and principal directions according to effective stresses. Moreover this method allows evaluation of the fracture porosity changes, which are then translated into consolidation of the medium..
  • Publication
    Accès libre
    Regional Flow and Deformation Analysis of Basin-Fill Aquifer Systems Using Stress-Dependent Parameters
    Preisig, Giona 
    ;
    Cornaton, Fabien Joel
    ;
    Perrochet, Pierre 
    Changes in effective stress due to water pressure variations modify the intrinsic hydrodynamic properties of aquifers and aquitards. Overexploited groundwater systems, such as basins with heavy pumping, are subject to nonrecoverable modifications. This results in loss of permeability, porosity, and specific storage due to system consolidation. This paper presents (1) the analytical development of model functions relating effective stress to hydrodynamic parameters for aquifers and aquitards constituted of unconsolidated granular sediments, and (2) a modeling approach for the analysis of aquifer systems affected by effective stress variations, taking into account the aforementioned dependency. The stress-dependent functions were fit to laboratory data, and used in the suggested modeling approach. Based on only few unknowns, this approach is computationally simple, efficiently captures the hydromechanical processes that are active in regional aquifer systems under stress, and readily provides an estimate of their consolidation.
  • Publication
    Accès libre
    Simulation of flow in fractured rocks using effective stress-dependent parameters and aquifer consolidation
    Preisig, Giona 
    ;
    Cornaton, Fabien Joel
    ;
    Perrochet, Pierre 
    Effective stress plays an important role in aquifer dynamics, especially in those affected by high variations of water pressures. Increasing/decreasing effective stresses affect hydrogeological parameters, even in media of high stiffness, such as fractured rocks. This study presents a modelling approach of groundwater flow in fractured rocks and aquifer deformation taking into account the dependency of hydrogeological parameters on effective stress. This approach has been illustrated by modelling a fractured aquifer dynamic, the Zeuzier arch dam settlement. The calibrated model showed agreement with measured data. This simulation method could be used to study the sensitivity of aquifers to variations in effective stress due to water pressure.
  • Publication
    Accès libre
    Modelling Discharge Rates and Ground Settlement Induced by Tunnel Excavation
    Preisig, Giona 
    ;
    Dematteis, A.
    ;
    Torri, R
    ;
    Monin, N.
    ;
    Milnes, Ellen 
    ;
    Perrochet, Pierre 
    Interception of aquifers by tunnel excavation results in water inflow and leads to drawdown of the water table which may induce ground settlement. In this work, analytical and numerical models are presented which specifically address these groundwater related processes in tunnel excavation. These developed models are compared and their performance as predictive tools is evaluated. Firstly, the water inflow in deep tunnels is treated. It is shown that introducing a reduction factor accounting for the effect of effective stress on hydrodynamic parameters avoids overestimation. This effect can be considered in numerical models using effective stress-dependent parameters. Then, quantification of ground settlement is addressed by a transient analytical solution. These solutions are then successfully applied to the data obtained during the excavation of the La Praz exploratory tunnel in the Western Alps (France), validating their usefulness as predictive tools.