MSc Students 2011-2012

Aeberli, Martin Paul

Stress Profile through the Central Gotthard Massif

The central part of the Gotthard Massif between Airolo and Sedrun shows low seismic activity and a poor coverage with in-situ stress measurements, even though a large number of underground excavations projects have been realized in this region, the most recent being the Gotthard Base Tunnel (GBT). In the Gotthard Massif section between the intermediate adits of Faido and Sedrun, the GBT has been excavated at a depth ranging between 1000 and 2500 meters and was confronted with stress induced failures of variable intensity. Such stress induced failures ranged from minor flaking to spalling and violent rock burst. These stress induced failures can be “back-analyzed” to characterize stress conditions around the tunnel excavation (primary and secondary stresses), if the appropriate strength properties of the rock are known. Such stresses in the central part of the external massifs of the Alps would be extremely valuable for many practical and fundamental questions. Therefore the goals of this MSc thesis are to carry out systematic back-analyses of stress induced failures along the central section of the GBT, the derive a high-resolution stress profile at tunnel elevation and to interpret this profile.

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Alpiger, Andrea Klara

Hydrogeology of the Great Aletsch glacier region

Recent observations in Swiss Alpine valleys have highlighted impressive natural rock slope deformations associated with a raising and lowering groundwater table throughout the year. In a glaciated catchment, portions of the groundwater regime are likely controlled by the glacial meltwater cycle, in contrast to adjacent unglaciated areas, therefore a unique annual groundwater signal may be expected. This project will focus on evaluation of the regional groundwater table around an active glacier through seasonal and spatial mapping of springs. Field data will help clarify how groundwater in rock slopes adjacent and down-valley of the glacier responds to changing ice extents. These outcomes can then motivate analysis of predicted hydro-mechanical deformations and progressive fracturing as ground-water conditions develop through time. The study area for this project is the Great Aletsch glacier, especially the areas between Riederalp and the Maerjelesee.

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Burkhard, Jonas Lukas

Donau, Jörg

Fries, Mathias Michael Andreas H.

Empirical and theoretical investigations on spatter blocks

Rock fall is a prominent hazard in steep mountainous terrain. Today numerous modeling programs simulating that kind of process exist on the market predicting the total kinetic energy, bouncing height etc. So far the development of spatters is not considered when a block falls e.g. on a road or another block. When a block is splitting up in many fragments the created spatters fly through the air like bullets and endanger life, damage buildings and constructions. This is not only a problem occurring in rock fall events but also during blasting. The overall goal of the study is to acquire the theoretical framework of the development of spatter blocks and to compare and calibrate the theory with real events as basic concept for further modeling. The work includes field work on several site studies where in a rock fall event or during blasting the formation of spatter blocks has been observed (e.g. Gurtnellen, Lopper tunnel, Lostallo, Kandersteg).

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Gschwind, Sophie Giacomina Elisabeth

The relationship between failure behavior of Opalinus Clay and sedimentary subfacies types

Many rock mechanical tests have been conducted on the Opalinus Clay. Most of these mechanical tests utilized specimens from the shaly facies. The mechanical properties of other facies types such as the sandy facies were only barley investigated and the geological knowledge gained from small scale mapping and thin section analysis were not sufficiently considered. This is of particular interest since new studies demonstrated that the mineralogical composition may have an influence on the mechanical properties. For example Klinkenberg et al. (2009) showed that the failure strength of the shaly facies decreases with increasing carbonate content due to localized accumulations of shell fragments. However, a clear link to the existing detailed small scale mapping with an adapted sampling strategy which encompasses all available subfacies types is still missing. The aim of this proposal is to fill up this gap and to profit from the detailed geological knowledge about the sandy facies, which has been elaborated in the framework of the SO experiment and other experiments the past 1.5 years.

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Gübeli, Markus Sebastian

The origin of annual pore-pressure variations in the Rotondo granite at 1 km depth

Since March 2000, pore pressure has been measured to 10 Pa precision in two intervals in a borehole drilled from the Bedretto gallery that intersects the Furka rail tunnel near its middle. The overburden at the intersection is about 800 m, and the rock is Rotondo granite. The intervals are approximately 30 and 45 m away from the nearest excavation wall, and show mean ambient pore pressure levels of 4.2 and 5.2 MPa respectively. Pore pressure variations due to the Solid Earth Tides, atmospheric loading and distant earthquakes are evident in the records. However, the largest variations occur at annual periods, and have magnitudes of approximately 0.17 and 0.22 MPa for the nearest and furthest intervals respectively. The form of the annual variation is not sinusoidal but rather saw-tooth like, involving a near-constant increase in pressure during summer and autumn, and a corresponding decrease in winter and spring. The reversal in trend occurs over a period of 2-4 weeks, and tends to be more rapid at the spring-summer event. The origin of the annual signal is uncertain, although it appears to be correlated with the presence or absence of snow cover on the mountains. As such, it could reflect a mechanism that is important for groundwater hydrogeology in Alpine areas. The objective of this thesis is to identify the factors that control the observed annual pore pressure fluctuation at 800 m depth.

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Hoffmann, Marc Emmanuel

Geomechanical Analysis of the rock slope instability Kilchenstock (Glarus)

The rock slope instability at the Kilchenstock is located close to the village Linthal, is well known since approximately 1200. In the 19th century a larger rock fall destroyed parts of the church. During the summer 1930 heavy rain fall events triggered several rock falls and mudflows reaching the village at the toe. In the same year Albert Heim recommended to evacuate the village due to an impending collapse of the entire rock slope. An estimated volume of 100’000 m3 of rock collapsed at this time, but a collapse of the entire slope did not happen. Several larger events followed in the following years (e.g. 1932) and protection embankments have been built. Recent observations of newly formed morphological features suggest that the scenario of a global failure as proposed by Albert Heim should be investigated in detail and eventually monitored.

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Koch, Simone

Borehole logging and hydrogeology of the Okavango Delta, Botswana

The Okavango delta is a largely closed basin that is a hugely important wildlife region that lies at the SW end of the East Africa Rift System. Although the surface hydrology has been well studied, little is known about the hydrogeological structure of the shallow subsurface. In 2007, extensive large-scale and high-resolution small-scale airborne transient electromagnetic surveys were flown to delineate the electrical conductivity structure of the shallow subsurface. These have been supplemented by surface geophysical surveys using seismics and radar. The results have revealed a structure that consists of a high-resistivity layer extending down to 50-100 m, succeeded by a low-resistivity layer that extends to the interface with a lower high-resistivity layer at about 200 m. The upper high-resistivity layer undoubtedly consists of gravels saturated with fresh water. However, the nature of the low two layers are uncertain. One hypothesis is that the low-resistivity layer represents a clay aquaclude overlying an unknown fresh-water aquifer that might be a proto-Okavango delta. An alternative is that the low-resistivity layer represents a zone saturated with salt water and that the underlying higher-resistivity body represents basement. There are no boreholes in the delta that are sufficiently deep to distinguish between the two hypotheses.

The Applied Geophysics group of the Geophysics Institute of the ETH Zurich, who have been leaders in the analysis of the airborne and surface geophysics data, have recently received approval to drill boreholes to 300-400 m depth in the delta to address the issue. One part of the research program will be to run geophysical logs in the holes to determine the hydrogeological nature of the shallow subsurface. The proposed Masters project will be to run the logs and participate in producing a hydrogeological model of the subsurface by jointly interpreting geophysical and logging data. The fieldwork will be conducted during October-November 2012, and the student must participate. Travel and accommodation expenses will be provided. The student must have successfully completed the course on borehole geophysics offered in the spring semester.

Kupferschmied, Nicolas

Hydraulic tomography in fractured rocks

During the last decade interest on the use of hydraulic tomography in hydrogeological investigation has substantially increased, primarily due to the ability to characterize heterogeneity in the subsurface at a high resolution. We will test in this study a travel time based tomographic methodology to characterize fractured rock aquifers. As application site the Lötschberg Base Tunnel in the Canton of Bern is chosen. The novel data acquisition is structured in three steps: 1) we examine in situ measurements collected previously in the Lötschberg Base Tunnel, to obtain the statistics to characterize the fractures, 2) the statistics will be used to create a stochastic model that captures the geometrical distribution of fractures, 3) random fracture realizations generated by the stochastic model will be transformed into a deterministic flow model. For each hydraulic discrete fracture model a suite of tomographic cross-well test will be simulated and inverted utilizing a travel time based inversion scheme. The results will give us the opportunity to get insights in the spatial diffusivity distribution of the test site and to verify the potential of the chosen inverse scheme to reconstruct the spatial distribution of the fractured systems.

Maselli, Maurizio Gregorio

Nagelisen, Jan Pascal Vincent

Obersee Rock Avalance

Reist, Fabian

Characterization of unconsolidated sediments based on hydraulic and tracer testing at the test site Widen, Thur valley

The objective of the proposed master thesis is to identify and to reconstruct hydraulic subsurface structures and their physical properties governing solute transport in unconsolidated porous aquifer materials. The master thesis comprises the following hydrogeological field and lab work that will be performed at the Widen test site in the Thur valley close to Frauenfeld:
• Installation of multi-chamber wells and wellbore coring
• Performance and analysis of sieve analysis
• Performance and analysis of multi-level slug tests
• Performance and analysis of multi-level cross-well pumping tests
• Performance and analysis of a forced gradient tracer test
The gained information will be used to set-up a numerical flow and transport model of the Widen site.

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Schlegel, Petra Anna

Detection of anhydrite with geophysical borehole logging methods regarding the application of shallow geothermics

Wymann, Linda Patricia

The influence of saturation on the strength of Opalinus Clay

After the excavation of a repository tunnel in clay rock such as Opalinus Clay the rock mass is exposed to relative humidity and temperature changes in the tunnel. These changes may have a seasonal variation. Low relative humidity in the tunnel may cause de-saturation of the rock around the tunnel (to a limited depth), higher humidity may cause re-saturation. It is well known that the strength of a clay rock depends substantially on the saturation degree. Thus, de-saturation may have a positive effect on the strength, re-saturation a negative. Observations in different Underground Research Laboratories revealed that seasonal changes in relative humidity and temperature cause increasing tunnel convergences in the long term and are thus relevant for the design of a repository tunnel.

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