Sarah M. Springman

Shallow seismic surveying of an Alpine rock glacier

To map the internal structure and lower boundary of an alpine rock glacier, we recorded three shallow seismic profiles and drilled four ∼70‐m‐deep holes through to the underlying bedrock. Although analysis of the seismic data using standard reflection processing schemes did not yield conclusive results because of the dominantly low‐frequency returned signals and the presence of strong source‐generated noise, tomographic inversions of first‐arrival times were successful in mapping several critical subsurface features. A thin, low‐velocity layer of loose boulders, air voids, and snow was found to extend across the entire surveyed area. Below this layer, two distinct velocity regimes superimposed on a general increase in velocity with depth were identified. A broad regime of high velocities was interpreted to contain boulders with numerous ice‐filled voids, whereas an adjacent regime of relatively low velocities was explained in terms of boulders with air‐ and water‐filled voids. This latter region of degrad...

A coefficient of restitution of rock materials

At a macroscopic scale, even a purely elastic contact between rock particles is accompanied by energy dissipation. The resulting hysteretic loop of the stress/strain path during such a loading and unloading event suggests that grains recover slower to their original shape than when they were first deformed. This contact behaviour may be simulated in distinct element codes by utilizing a hysteretic damping contact model. In this research, values for the elastic coefficient of restitution for components of a molasse conglomerate were measured using a newly developed drop-test apparatus. These values can be used to calibrate or to verify constitutive models that incorporate strain-rate-independent, elastic hysteretic damping.

MULTIDISCIPLINARY INVESTIGATIONS ON THREE ROCK GLACIERS IN THE SWISS ALPS: LEGACIES AND FUTURE PERSPECTIVES

Abstract This paper recognizes the contribution of Professor Wilfried Haeberli for his inspiration and leadership in the field of permafrost science and his generous encouragement, both direct and indirect, to the ETH Researchers who have, through him, endeavoured to contribute to this fascinating research area. The multidisciplinary investigations described in this paper have focused on three rock glaciers, Muragl, Murtèl‐Corvatsch and Furggwanghorn, all of which have been subject to a varying degree of prior study, and which are continuing to attract new generations of researchers to understand and explain the processes and predict future behaviour. This paper marks a stage at which it is possible to summarize some advances in the state of the art and associated innovations that can be attributed to early motivation by Wilfried Haeberli and offers a tribute as well as gratitude for his ongoing feedback and advice. Some thoughts on the development of thermokarst due to water ponding and flow, and a conceptual model of geotechnical mechanisms that aim to explain some aspects of rock glacier kinematics, are also introduced.

Modelling of soil-structure interaction for a piled bridge abutment in plane strain FEM analyses

Abstract Full-height piled bridge abutments constructed on soft clay are prone to soil–structure interaction effects. A series of geotechnical centrifuge tests of this type of structure has been undertaken, and an accompanying series of plane strain finite element analyses are reported. Some aspects of the structure do not conform to a plane strain analysis (most notably the piles), and the methods used to incorporate this soil–structure interaction are described. Success of the methods is illustrated by good comparison with the centrifuge test results, and the numerical analyses revealed interaction effects which could not be specifically identified in the centrifuge tests.

Landslide triggering experiment in a steep forested slope in Switzerland

A landslide triggering experiment was carried out on a 37°- 40° steep forest slope in North-East Switzerland by sprinkling water artificially to represent an extreme rainfall event. This project is part of a multidisciplinary collaboration, which includes geotechnical engineering, hydrology, hydrogeology, forest engineering, geophysics and photogrammetry. A three dimensional model of the ground was developed from non-invasive geophysical surveys, insitu probing, combined sprinkling and dye tracer tests and shallow test pits. Laboratory tests were carried out on undisturbed samples under various degrees of saturation This paper mainly focuses on the characterisation of the site.

Experimental modelling of debris flow behaviour using a geotechnical centrifuge

Physical modelling of debris flows has been carried out in the geotechnical drum centrifuge at ETH Zurich. A new apparatus to model debris flows in the centrifuge is described. The apparatus permits the final reach of a typical debris flow to be modelled within the centrifuge, with unconsolidated material flowing down a slope to deposit as a fan around the drum. Experiments are described for both fixed base conditions and erodible bases. Tests to examine the verification (modelling) of models show that debris flow behaviour is governed mainly by friction and consolidation processes, although some resolution is required between flow behaviour downslope and flow arrest during runout. The results are compared with bulk parameters determined for field-scale debris flows. It is found that some important flow mechanisms, such as contact-dominated behaviour and high pore pressures, are developed that are closer to those developed at field-scale than tests conducted at 1g. Velocity profiles for erodible beds are ...

Contemporary glacier retreat triggers a rapid landslide response, Great Aletsch Glacier, Switzerland

The destabilization and catastrophic failure of landslides triggered by retreating glaciers is an expected outcome of global climate change and poses a significant threat to inhabitants of glaciated mountain valleys around the globe. Of particular importance are the formation of landslide-dammed lakes, outburst floods, and related sediment entrainment. Based on field observations and remote sensing of a deep-seated landslide, located at the present-day terminus of the Great Aletsch Glacier, we show that the spatiotemporal response of the landslide to glacier retreat is rapid, occurring within a decade. Our observations uniquely capture the critical period of increase in slope deformations, onset of failure, and show that measured displacements at the crown and toe regions of the landslide demonstrate a feedback mechanism between glacier ice reduction and response of the entire landslide body. These observations shed new light on the geomorphological processes of landslide response in paraglacial environments, which were previously understood to occur over significantly longer time periods.

Rock Glacier Degradation and Instabilities in the European Alps: A Characterisation and Monitoring Experiment in the Turtmanntal, CH

Global climate change is impacting sensitive alpine cryogenic regions, through slope instabilities in rocks and soils. Significant temperature increase at the air-ground surface interface may be accompanied by increased rainfall, more extreme storms and additional severe rise in mean global temperatures in the coming decades, enhancing risk of mass movement hazards to human life and infrastructure. Rock glaciers and degrading permafrost on steep Alpine slopes are particularly susceptible to warming and phase change in either massive or interstitial ground ice, which may lead to release of water, accelerated motions, initiation of landslides and instabilities. Accumulated failure in soil elements, determined on artificial frozen specimens of rock glacier materials at temperatures below 0 °C, is linked to these processes at field scale. A geophysical and geotechnical field characterisation and monitoring experiment is being conducted on a rock glacier that is undergoing thermally induced creep and growth of thermokarst. Preliminary investigations are described in this contribution.

Mechanisms controlling the behaviour of double-porosity clay fills; in situ and centrifuge study

Abstract Two instrumented embankments built on a double-porosity landfill of clayey lumps were monitored in situ and modelled in a geotechnical drum centrifuge. Field measurements of hydrostatic levelling, depth reference points and pore pressure gauges showed high and variable compressibility of the landfills. Introductory modelling in a mini-centrifuge, combined with oedometer testing, demonstrated the key mechanisms in the double-porosity fills: irreversible deformation at low stress ranges as a result of rearrangement of the lumps, and reversible deformation (swelling) at higher stresses, similar to the behaviour of reconstituted material. Placing fill under water resulted in high initial void ratios followed by large deformations while loading. Dry filling followed by saturation may be recommended for further development of the landfills in future. Data from the geotechnical centrifuge models confirmed that permeability was controlled by the complex structure of the clay fills. Similarly to the field measurements, there were significant initial settlements on loading as a result of compression of open macro-voids. The double-porosity structure in the fresh fill allowed excess pore pressures to dissipate quickly, which accelerated the consolidation process initially. Thereafter, dissipation was controlled by the permeability of the intragranular pores in the clay, once the intergranular pores had closed.

Numerical modelling of slope–vegetation–atmosphere interaction: An overview

The behaviour of natural and artificial slopes is controlled by their thermo-hydro-mechanical conditions and by soil–vegetation–atmosphere interaction. Porewater pressure changes within a slope related to variable meteorological settings have been shown to be able to induce soil erosion, shrinkage–swelling and cracking, thus leading to an overall decrease of the available soil strength with depth and, ultimately, to a progressive slope collapse. In terms of numerical modelling, the stability analysis of partially saturated slopes is a complex problem and a wide range of approaches from simple limit equilibrium solutions to advanced numerical analyses have been proposed in the literature. The more advanced approaches, although more rigorous, require input data such as the soil water retention curve and the hydraulic conductivity function, which are difficult to obtain in some cases. The quantification of the effects of future climate scenarios represents an additional challenge in forecasting slope–atmosphere interaction processes. This paper presents a review of real and ideal case histories regarding the numerical analysis of natural and artificial slopes subjected to different types of climatic perturbations. The limits and benefits of the different numerical approaches adopted are discussed and some general modelling recommendations are addressed.