Browsing by Author "Ladefoged, Julia"

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Microstructures and Compressive Strength of Lake Ice in Sweden A structural Documentation and Compressive Strength Analysis of Lake Ice Cores from Uppsala, using the SonReb Method
(2023-08-18) Ladefoged, Julia; University of Gothenburg/Department of Earth Sciences; Göteborgs universitet/Institutionen för geovetenskaper
Lake ice have been utilized by humans through centuries, as transportation routes and recreational activities to name a few (Sharma et al., 2019). Despite our frequent usage of lake ice there is a lack of extensive knowledge of it. In contrast to sea ice and continental ice, microstructures of lake ice have been sparsely investigated (Kirillin et al., 2012), and current research lack visual documentations and extensive descriptions. microstructures in lake ice and their relation to compressive strength could increase our understanding of different ice characteristics and mechanical properties of lake ice, and furthermore provide valuable information to minimize the risks of traveling on ice. This thesis provides a high resolution documentation of microstructures and grain geometries of 5 lake ice cores from 3 different lakes. Furthermore, the thesis explore the possibilities of using the SonReb method to determine the compressive strength of lake ice. The 5 investigated ice cores display two distinct structural patterns. The first pattern consist of large grained transparent ice with preferred vertical c-axis distribution, interpreted as a S1 ice. On top of the S1 ice there is a fine grained opaque ice with randomly oriented c-axes, interpreted as a superimposed T1 ice from Michel’s(1971) classification. The second type consist of a layered ice with lenses of larger grains with varying sizes, with preferred vertical c-axis orientation. The lenses are enclosed in a matrix and alternating layers of a smaller grained ice with a preferred c-axis orientation superimposed on a random orientation. No existing formation model can fully explain the observed layered structure, which clearly demonstrates the necessity of further research of microstructures in lake ice. Due to instrumental complications with the Schmidt hammer and the uniaxial press, only relative uncalibrated strengths could be determined with the ultra sound. The measurements indicate a slightly larger vertical compressive strength compared to other orientations(30°, 60°, Horizontal, 120° & 150°), as well as an increased strength in litoral samples compared to pelagic ice samples.
Structures of the deep bedrock in Gothenburg. A structural documentation of the GE1 drill core
(2021-07-12) Ladefoged, Julia; University of Gothenburg/Department of Earth Sciences; Göteborgs universitet/Institutionen för geovetenskaper
Gothenburg Energy, SGU and Gothenburg University are currently investigating the possibilities of a deep geothermal energy plant in Gothenburg. In their first investigations there have been a 1 km drilling in Högsbo. The aim of this thesis was to provide a structural documentation of the rocks from the first 555m of the Gothenburg Energy 1 (GE1) drill core, as well as determining the rebound number and the P-wave propagation time through different lithologies of the drill core. The lithologies and radioactive isotope concentrations has been described by Hynynen (2021) and a combined log of the core will be included in both theses. The foliation throughout the core is generally dipping gently to moderately to the south, southeast and north, relative to the orientation, however the foliation is changing with depth. The fractures of the core exhibit different dip and dip direction depending on depth, but most of the fractures are dipping moderately to gently to the east and southeast. There is no indication of increased number of fractures with depth. The angular relation between mean foliation sets and mean fracture sets indicate there are older fractures which have been folded with the foliation and younger fractures which cross the foliation. Overprinting foliation and folded folds have been observed at several locations, implying at least two different deformation events have altered the bedrock. Measured Lineations on fracture planes are mostly plunging steeply, indicating vertical movements. Lineations on foliation planes are plunging gently to the N-S and NW-SE, resembling the orientations of the intersection lineations from the observed overprinting foliations. They could therefore be interpreted as lineations with similar origin. Further research is needed to draw any conclusions from the investigated mechanical properties. Similarly further investigations are needed to evaluate if Högsbo would be suitable for a deep geothermal energy plant.