Hydraulic conductivity relations in soil and fractured rock : fluid component and phase interaction effects

Sammanfattning: The hydraulic conductivity of soil and fractured rockdetermines the rate at which fluids and dissolved chemicals flowthrough the subsurface, for given conditions at the boundary.Hence, the estimation of relevant parameters for quantificationof hydraulic conductivity relations constitutes a critical basisfor accurate model predictions. This dissertation addressesdifferent phenomena affecting hydraulic conductivity.Specifically, hydraulic conductivity relations in the presence ofa non aqueous phase in soil are investigated through laboratory,field and model studies. Results show that the volatilisation ofa multicomponent non-aqueous phase liquid (NARL) can lead toconsiderable changes in the chemical NAPL tomposition and thephysical NAPL properlies, such as viscosity. Apart from theexpected influence of changed viscosity, the changes in chemicalNAPL tomposition greatly influence the NAPL conductivity ininteracting soils (clay and peat). Moreover, pore sizeheterogeneity and macropore existence atTect relative hydraulicconductivity. A relatively simple procedure is presented fordetecting such heterogeneities in the laboratory. The procedureprovides consistent evidente of pore-size homogeneity in pornusmedium samples.Methods are developed for the measurement and estimation ofunsaturated transmissivity relations in fractured rock. They areapplied to the case of degassing of deep groundwater, which is aphenomenon that may influence the characterisation of fracturehydraulic properties, e.g., in investigations related to thefinal storage of radioactive nuclear waste in deep bedrock.Modelled relative transmissivities are found to be sensitive toassumptions regarding phase occupancy in different fiactureaperture regions. The asauroption that both water and gas canco-exist in wide aperture regions is consistent with laboratoryobservations of both the actual gas phase occupancy and relativetransmissivities in transparent rock fracture replicas underdegassing conditions. Derived model resuhs are also consistentwith field observations of the occurrence, or the absente, ofdegassing effects for different boundary pressures and bubblepressures. The statistical description of fi-acture aperturevariability used in the developed models provides an alternativeapproach to tommon porous medium type of relative hydraulicconductivity relations for unsaturated flow. It may also beuseful in various applications involving two-phase flow infiactured rock. For groundwater degassing applications, resultsimply that degassing effects in borehole tests of singlefiactures should generally be small.Keywords:hydraulic conductivity, unsaturated flow,transmissivity, NAPL, multi component liquid, mass transfer,soil, pore size distribution, drainage curve, fractured rock,aperture distribution, bubble pressure, degassing, nuclearwaste.