Instabilities in alpine permafrost: strength and stiffness in a warming regime e-bog

Global climate change is contributing to hazards to infrastructure in cold regions, asengineers try to quantify uncertainties through a risk-based consideration of sensitivity andconsequences, and thereby to mitigate the risks arising from permafrost degradation. Agradually rising Mean Annual Air Temperature, combined with more extreme rainfallconditions and fewer 'freezing degree days', mean that the water phase in soil that has beenfrozen for many years in the form of permafrost, is likely to thaw and release groundwaterinto the voids. Since the properties of warm permafrost can change significantly as itstemperature rises, climate change can affect not only the thickness of the active layer andthe depth of permanently frozen ground, but also the constitutive behaviour of the permafrostlayer. This has significance not only for movements and stability in permafrost slopes butalso in rock glaciers, which are ice-rich geomorphological landforms. Furthermore,permafrost degradation is causing changes in land surface characteristics and drainagesystems, as warming of rock glaciers leads to accelerated creep. Instabilities may also betriggered as the constitutive properties of permafrot change, either in the form of active layerdetachments or at depth through the warming permafrost. Catastrophic debris flows mayalso occur. Dr Yamamoto has conducted a fundamental and highly innovative experimental investigationinto the effect of time and temperature on the creep and shear strength properties ofanalogue alpine permafrost, under a range of stress conditions that would be experienced indifferent locations of a rock glacier. She has developed new equipment to maintain thetemperature in the frozen soil specimens at C in the previously unexplored rangebetween 0 and -0.5C, and to record acoustic emissions during creep and shearing. Furthermore, she has carried out novel micromechanical investigations into the changesoccurring in the solid, ice, air and unfrozen water mixture as a result of shearing. The resultsof the laboratory tests have been used to provide a deeper insight, not only into theconstitutive behaviour of frozen soils, but also a greater qualitative understanding of thegeotechnical performance of rock glaciers under warming conditions. In addition, she has extended an existing mechanical constitutive model for soils thatincludes both soil creep and shear behaviour to develop a semi-coupled Thermal-Hydro-Mechanical (THM) constitutive model. The model, when implemented in a finite elementpackage, allows the laboratory element test data to be predicted, which also validates keyaspects of her model rather well. This represents a significant step towards achievingquantitative predictions of the influence of temperature variation on the performance of rockglaciers. Dr Yuko Yamamoto has made original and significant discoveries about the thermomechanicalresponse of frozen soils under a range of stress path tests, by developing andusing a range of state-of-the-art experimental techniques and combining these with powerfulanalytical and numerical methods to interpret and model behaviour of permafrost soils. Herresearch paves the way for future work that will lead to quantitative modelling ofgeomorphological process in permafrost landforms, such as the creep and stability of rockglaciers. Prof. Dr. Sarah M. Springman II CBE FREng