Kim, F.; Penumadu, D.; Gregor, J.; Kardjilov, N.; Manke, I.; Schulz, V.; Wiegmann, A.: High Resolution Dual Modality (Neutron and X-ray) Imaging of Partially Saturated Sand and Direct Numerical Simulation Based on Realistic Microstructure. In: 46th US Rock Mechanics/Geomechanics Symposium 2012 : Chicago, Illinois, USA, 24 - 27 June 2012 / [ARMA, American Rock Mechanics Association]. , 2012, p. 12-465/1-7

Abstract:
High resolution neutron (~13.7 μm/voxel) and X-ray (~11.2 μm/voxel) tomography imaging of partially water saturated sand specimens was performed at Helmholtz Zentrum Berlin (HZB). Two different sand grain morphologies (round and angular) were used. Partially saturated silica sand is a three phase material consisting of solid phase (Silica: SiO2), gas phase (air), and liquid phase (water). Due to different attenuation characteristics of neutrons and X-rays to these three phases of interest, neutron and X-ray images provided unique but complementary information. While the water phase contrast is well identified with cold neutron images without using a contrast agent, the detailed structure of silica sand phase is much clearly shown in X-ray images due to low attenuation of air/water phases to X-rays. A detailed description of neutron and X-ray tomography for visualizing and quantifying microstructure of an assemblage of sand grains is provided in this paper. An automatic approach to register the dual modality image information in the same coordinate is also demonstrated and a technique to match different resolutions from neutron and X-ray imaging techniques is addressed. Direct numerical simulation technique based on the realistic pore geometry obtained from X-ray tomography of dry sand specimen is also demonstrated. Pore morphology method was used to obtain simulated capillary water distribution and capillary pressure – saturation curve for dry sand specimen with complex initial void size distribution in three dimensions based on the measured tomography data