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Breaking the ice

Sarah Springman, who at the end of 1996 left Cambridge University to take the chair of geotechnical engineering at Zurich's Federal Institute of Technology, provides a personal view on geotechnical research in Switzerland.

Apart from the obvious changes in languages and culture, leaving Cambridge for Switzerland necessitated a new engineering outlook, particularly in terms of the impact of the local landscape and the temperature regime. From Fens to Alps, one difference is immediately clear - that of a large scale vertical dimension.

The amount of 'stored' potential energy in future 'soil' at above 2,500m to 3,000m, both as it remains on a rock face, and even immediately after weathering in an accumulation zone, is considerable. Periodically this is briefly exchanged for kinetic energy, with significant associated damage.

Recent collaborative activity in Switzerland has caused several research and governmental groups to be combined into a Natural Hazards Commission (CENAT)*. The strongly rising incidence of large scale natural events which can severely damage existing infrastructure, has forced the local councils, cantons and federal government to move from a policy of total safety (at all costs) to that of a risk culture.

Of interest to the geotechnical engineers are problems associated with landslides, debris flows, earthquakes and melting of alpine permafrost, which fall alongside analogous work on avalanches, rockface and glacier instabilities. However, the intention is that multidisciplinary research teams may be formed, drawing from whatever range of expertise that may be necessary to find the best solution - essentially a problem rather than a discipline-oriented approach.

One area of concern is the melting of so-called warm alpine permafrost (0degrees to -3degreesC), which collects as a frozen mass of ice and granular material (of all sizes) at above 2,500m altitude, and creeps slowly downhill at a rate of up to 0.5m per year.

Until very recently, research in this area has been the preserve of geographers, geomorphologists and glaciologists, although the new Permafrost & Climate in Europe (PACE) project is also beginning investigations from a geotechnical engineering viewpoint**. With the increasing likelihood of thaw to significant depths, the associated behaviour changes from essentially cohesive (but creeping) to granular and frictional, hence more geotechnical understanding is required.

The complex inhomogeneity of these creeping permafrost bodies, or rock glaciers, is influenced by local geometry, including the supply of newly weathered rock and snow. The temperature, particle size distributions and the relative percentage of ice, soil and air play a major role in controlling both the time-dependent deformation and the likelihood of failure occurring within this flowing mass of up to several million cubic metres of material.

In summer, the frozen soil melts down to a certain depth allowing an 'active' layer, which is alternately frozen and thawed (dependent on the season), to be formed. Water flow in this layer can often be a source of instability, and in 1987 several failure events occurred in the Alps due to melting of ice just within or above the permafrost. With the current fear of ambient temperature rise, it is likely that increasing volumes of material will belong in the active zone, and that greater volumes of interstitial ice (and snow) will melt each year.

Consequently, a programme of research is now under way to establish the spatial distribution of material within a rock glacier (including depth to solid rock). A combination of surface geophysics, cold air drilled boreholes and cross hole geophysics will be performed.

Secondly, the thermo-mechanical response of the frozen material will be investigated, mainly using laboratory triaxial tests on the undisturbed cores obtained from the boreholes. Temperature, stress level and strain rate will be varied for monotonic tests to failure. Creep tests at a varying percentage of the expected failure load will also be carried out.

Finally, the boreholes will be instrumented and used to deliver depth related data of temperature and deformation (until the inclinometers shear off). In addition, surface measurements of temperature and deformation will be conducted.

Preliminary numerical analysis of the rock glacier flow will also be carried out to investigate the growth of some of the unusual surface

features which develop near the snout of the rock glacier. This will be a prelude to more detailed numerical analysis at a later stage which will incorporate an appropriate constitutive model with the data obtained from the geotechnical testing.

Ultimately, it is intended that a combination of surface geophysics and numerical analysis may be used to predict when degrading permafrost may be approaching instability.

The Institutes for Geotechnical Engineering, Geophysics and the Laboratory for Hydraulics (Glaciology section) from the Swiss Federal

Institute of Technology, Zurich (ETHZ) are combining in the research team, funded for three years from 1 September by the ETHZ research fund. Investigators are: Professor Sarah Springman, Lukas Arenson, Dr Ashraf El-Hamalawi (Geotechnics), Dr Hansruedi Maurer, Martin Musil (Geophysics) and Dr Daniel Vonder Muehll, Dr Hilmar Gudmundsson (Glaciology).

Contact: springman@igt.baum.ethz.ch

Complementary contacts

*Competence Centre for Natural Hazards (CENAT):

http://www.cenat.ch

**Permafrost & Climate in Europe (PACE):http://www.cf.ac.uk/uwc/earth/pace/

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