Calibrating HPT-profiles with micro-CT scans using upscaling from pore to field scale

Abstract

The potential of calibrating HPT-profiles with micro-CT scans using upscaling from pore-scale to field-scale has been investigated. Undisturbed samples ranging from clayey silt to fine sand have been retrieved along a 9m deep HPT-profile and taken to the laboratory. Kapton® polyimide tubes ranging from 3-5mm were pushed into the cores and sealed on both sides for micro-CT scanning with a Zeiss Xradia 610 Versa with a voxel size ranging between 0.56 – 2.02μm. A pore-network-model was extracted from the segmented images and loaded into PoreFlow to determine absolute hydraulic conductivities. An HPT-profile is calibrated to the results obtained with micro-CT scans and compared to 0.5 – 2m slug tests along the profiles for verification. HPT is not suited for low-K soils. Therefore, we focus our comparison between lab, field and HPT test on sandy soil types. Good results were observed when the profile is calibrated to samples obtained from a fine sand section. To expand this workflow to coarser soil types, the use of sodium silicates, known as waterglass is assessed in retrieving coarse undisturbed soil samples by gelatinizing the pore space making the sediments more cohesive. The technique shows potential in combination with micro-CT scanning as an appliance for retrieving undisturbed coarse materials from the subsurface.