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

Abstract: 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.