MSc Students 2014-2015
Rachael Marie Colldeweih
The Geological investigations of selected Theban Tombs, Luxor (Egypt)
The Theban Tombs at Sheikh Abd el-Qurna, also known as Tombs of the Nobles, are located a few kilometres west of the river Nile close to Luxor, Egypt, between the famous Valleys of the Kings and Queens. Starting about 4000 years ago, the Theban Tombs were cut into a tilted sedimentary rock sequence that belongs to the Theban Formation of Tertiary age. Many of the rock cut tombs show partial or entire collapse of pillars and ceilings.
The primary aim of the thesis is a detailed documentation of the geological settings of specific tombs of the Theban Necropolis and to evaluate potential causes of early tomb damage. Therefore, it will be necessary to develop detailed geological maps of the tombs and their surroundings. Mapping will focus on lithology and on rock mass structures, such as fractures, faults, and tension cracks. Geological structures will be identified and characterised with standard in-situ investigation, aerial photo interpretation, and with analysing new and existing photogrammetric models and laser scans to obtain fracture statistics of the different sedimentary rock layers.
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Nathaniel Coupy
Assessing photogrammetric approaches for rock mass characterization in underground excavations
Geological mapping of underground excavations is an important task for engineering geologists. It is used as a record of geological evidence, for short-term assessment of support requirements or as back analysis for further fine-tuning of geological models. The process of hand mapping in an underground environment is however challenging, time-consuming, potentially dangerous, and relies on the subjective observations of the operator with limited objective documentation.
Photogrammetry is a process that allows the reconstruction of 3D models through a pair of 2D photographs, using the representation of the same object from various points of view. The process has been in use and studied extensively above ground, proving to be efficient. Photogrammetry were also applied underground, in order to improve the geological record, decrease the mapping time and improve safety. The main tasks studied to date include geological and structural characterisation of the rock mass, assessment of rock damage and deformation (convergence) and study of structural and technical elements, such as as-built profiles.
For this thesis, the Solbakk tunnel, part of the Ryfast project in the area of Stavanger, Norway, has been used to gather photogrammetric data for rock mass characterisation and to compare with traditional mapping and logging methods. The contractor uses the splatter approach for photogrammetry data collection and provided 3D models for further analysis and comparison to the systematic fan approach used for the data collected as part of this thesis.
This thesis investigates the applicability of the photogrammetric approach to rock mass characterisation in a drill and blast tunnel. The two different acquisition methods (splatter approach and systematic, fanned approach) were compared in terms of similarity in the resulting 3D models. When applied to underground mapping, performed at an industrial scale, the models’ accuracy proves to be rather insensitive to the collection method. The fan project tends to provide greater detail quality for the smallest structures, while undergoing greater line of sight occlusion. This is counterbalanced in the case of the splatter method, where the dynamic approach reduces the occlusion but requires higher ISO to overcome the lack of stability, decreasing the image quality.
The rock mass characterisation focused on the RQD, Q-value, RMR and GSI determinations, based on 17 drill and blast faces, modelled in 3D by the contractor, using the splatter approach. The RQD values obtained based upon the 3D models were compared to the equivalent borehole value and prove to be of equal magnitude, if a bit greater. In addition, oriented RQD determinations were conducted on selected faces, by analysing separately the face and the walls of a same model. The difference in RQD value is negligible (about 5%). Moreover, the holistic approach prevents excessive bias due to orientation.
The Q-values determined on the basis of the models have been compared to the values assigned by the project geologist through conventional face mapping. The results from the photogrammetric approaches are slightly more optimistic, although always in the same order of magnitude and rock mass class. The RMR and GSI values obtained on the basis of the 3D models are in the range of the rock mass classes derived from the Q-index.
The parameters needed for the calculations of the rock mass classes related to the mid to large scale geometry of the discontinuities, such as spacing, length, orientation, or derived RQD, can be reliably determined on the basis of photogrammetric 3D models. Some parameters focussing on textural elements, such as alteration, weathering or small-scale roughness, can be inferred with the help of photogrammetry if they are prominent, such as coloured alteration of the rock or if the images are detailed and close-up view of the rock face. Eventually, parameters related to rock material strength or in-situ stress field must be determined through external sources, such as literature review, laboratory tests or onsite measurements.
The photogrammetric approach proves to be time-efficient and provides valuable results that are similar to the traditional methods, such as borehole logging and face mapping. The 3D models are believed to provide a broader amount of information, overcoming the orientation bias inherent to a borehole or the bias due to the operator.
Martin Benjamin Engeler
Kristina Elsbeth Ernst
Analysis of the impact of exfoliation fracturing on rockfall hazards in the Upper Aar Valley
Glacial erosion and retreat produce steep landforms prone to rockfall, while time-dependant weathering processes and fracture propagation loosen rock blocks promoting detachment. Some observations in alpine valleys point to elevated slope failure activity in areas of greatest stress release by deglaciation, while others emphasise the role of stress redistribution and induced fracturing, i.e. exfoliation fractures. Some studies reveal spatial correlation between glacial trimlines and landslide activity, while others suggest that most slope failures originate from weathered slopes above the ice limit. Clearly, determination of the relationship between glacial erosion, topographic form, age of surface exposure, exfoliation fracturing and rockfall activity is not easy.
This project will focus on mapping rockfall release areas in the Grimsel region of the Central Alps and correlating these with the local fracture patterns (especially exfoliation fractures) and measures of topographic form. In addition, known surface-exposure ages of the bedrock surfaces at different elevations, and rock mass quality will be considered. Rockfall release areas are defined here as parts of the slope where blocks have detached since glaciers last eroded the surface, being evident as sharp casts and corners in contrast to smoothed glacial surfaces.
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Martin Philipp Jung
Erin Rose Pilaar Lindsay
Monitoring and mapping groundwater induced rock slope deformations near the Lago Bianco Pump Storage Plant
The objective of this MSc thesis is to prove the hypothesis of groundwater pressure related reversible deformations of Alpine mountain slopes. For this purpose we will build and install permanent GPS and possibly also climate stations at one or two borehole locations of the Lago Bianco Pump Storage project (early summer 2015). Then the student will map geotechnically and hydrogeologically relevant properties in a section through the investigated boreholes (summer/fall 2015). In 2016 the coupled hydro-mechanical behavior of the mountain slopes in these sections will be studied in detail, mainly based on 2D numerical modelling of recharge induced groundwater pressures and surface deformations with the codes SEEP/SIGMA or RS2.
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