Triaxial constant stress and constant strain rate tests on ice-rich permafrost samples

Abstract

A range of mechanical compression tests were conducted on frozen soil samples at temperatures close to the melting point of ice to determine both the creep and the strength properties under triaxial stress conditions. The samples were obtained from two rock glaciers in the Swiss Alps. For comparison, additional samples were prepared artificially for testing. The results showed that the minimum creep strain rate increases exponentially with increasing temperature and applied deviatoric stress. The applied strain rate is the main parameter influencing resistance. However, test results show that the micromechanical behaviour is similar for all tests and independent of the applied loading condition. Measurements of the volumetric strain showed that the sample composition has a major influence, so samples with high air void ratios resulted in continuous contraction (i.e., reduction of the sample volume), whereas samples with low volumetric air and ice contents demonstrated dilatant behaviour.Key words: permafrost, frozen soil, creep, strength, triaxial testing, self-healing.

A new model for estimating subsurface ice content based on combined electrical and seismic data sets

“…For a porosity of 0.5 (Arenson and Springman, 2005 found porosities between 0.4-0.8 from boreholes in Muragl rock glacier) this leads to a solution space between around 600-4500 m s −1 and above 1000 m, depending on the prescribed values given in Table 1. A quick evaluation of the model performance can be performed by analysing the extreme cases of high air, high water and high ice contents.…”

“…At both field sites borehole data and additional geophysical data are available for model validation (Musil et al, 2002;Maurer et al, 2003;Arenson and Springman, 2005;Hilbich et al, 2009). The tomographic geoelectric and refraction seismic data sets for the case studies presented here were obtained during several field campaigns and include an almost 300 m cross profile near the tongue of Muragl rock glacier and a shorter 145 m longitudinal profile at Murtèl rock glacier (Fig.…”

“…5d). Ground temperature is measured in the boreholes using a thermistor string attached to a data logger and is available every 6 h, laboratory analysis of core samples regarding ice-, air-and rock content are only available from boreholes BH 4/99 at Muragl and BH 1/00 at Murtèl (Arenson and Springman, 2005). Hereby, the ice content was determined by melting the sample, analysing the volume of the solid particles and calculating the volume of the air and ice by assuming that the specific gravity of ice at a temperature close to the melting point is 0.917 Mg m −3 .…”

“…The volume of the unfrozen water was neglected. Due to uneven sample surfaces, Arenson and Springman (2005) cautioned that the calculated volumetric ice contents can be under-and the volumetric air contents overestimated for samples with high contents of solid particles. …”

“…However, except for laboratory analysis of field probes obtained near the surface or within boreholes (e.g. Arenson and Springman, 2005), the composition of the subsurface material can only be inferred through indirect geophysical investigations (for a review see Hauck and Kneisel, 2008 and references herein). Due to the complexity of the subsurface, a combination of geophysical methods (e.g.…”