Mapping and Analysis of Exfoliation Fractures with Emphasis of Exfoliation Joint Spacing in a New Gallery of the Upper Aare Valley, Central Swiss Alps

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Mapping and Analysis of Exfoliation Fractures with Emphasis of Exfoliation Joint Spacing in a new Gallery of the Upper Aare Valley, Central Swiss Alps

Project Framework: At present, a new gallery is excavated with drill and blast between Handegg and Gerstenegg in the Central Aar Granite of the Upper Aare Valley. Most of the gallery is unlined. The area is well-known for exfoliation joint sets (Talklüfte), i.e. relatively young joint sets that are parallel to today's or a former landscape surface. These joints can have a major impact on the stability and safety of near-surface excavations, tun- neling performance, and they can decisively influence the stability of slopes. In addition, exfoliation joints are characteristically restricted to the shallow subsurface with a maximum depth of around 100-200 meters and their spacing is thought to increase with depth (e.g. Jahns 1943).

In order to understand the formation mechanisms, the underlying stresses, lateral distribution, and depth development of exfoliation in an Alpine setting, the Chair of Engineering Geology is currently doing research on this topic using several approaches including mapping, numerical modelling, and also laboratory tests are planned. This project will contribute to our present research.

Project Goals and Approach: The goal of this thesis is to map the excavation surfaces (sidewalls) of this new gallery, with special emphasis on exfoliation joint sets, and to analyze the resulting geometric fracture properties (length, spacing, orientation) in the context of gallery depth and current land surface orientation above the gallery. Mapping of the gallery (probably a few weekends in summer 2011) might be complemented by mapping of existing core. Further galleries in the vicinity will also help you to collect data concerning exfoliation.

Exfoliation joint spacing in the Upper Aare Valley shall be analysed statistically and compared with data from other areas of different morphology and tectonic setting. Existing theories to exfoliation joint spacing are to be tested (e.g. Johnson 1970). You will also have the option to model exfoliation fractures with a numerical code (FRACOD; e.g. Lanaro et al. 2008).

You will learn fundamental techniques of engineering geological data acquisition, statistical analysis of fracture properties including computer based data processing, and visualization. You are welcome to also propose new ideas.

Main Supervisors: Prof. Simon Löw, Co-Supervisor: Martin Ziegler

Suggested Reading: Jahns, R. H. (1943): Sheet structure in granites: its origin and use as a measure of glacial erosion in New England. In: The Journal of Geology, 51 (2): 71–98. Johnson, A. M. (1970): Physical processes in geology. A method for interpretation of natural phenomena - intrusions in igneous rocks, fractures and folds, flow of debris and ice. 577 pp. San Francisco: Freeman, Cooper & Company. 357-399 pp. Lanaro, F.; Amemiya, K. & Yamada, A. (2008): Modelling the formation of sheeting joints with FRACOD2D (FRActure propagation CODe). In: Lanaro, F.; Matsui, H. (ed.): BEM-DDM modelling of rock damage and its implications on rock laboratory strength and in-situ stresses (JAEA-Research, 2007-093): 151–177. Sutter, B. (2008): Kluftmuster und Kluftgenese am Grimselpass. Geologisch-geotechnische Eigenschaften und Tiefenwirkung der Trennflächensysteme. Masterarbeit. Betreut von Prof. Dr. Simon Löw und Dr. Keith Ev- ans. 97 pp. ETH Zürich, Geologisches Institut.

For further information please contact Martin Ziegler (NO G 65, Phone: 044 632 23 42, Email: [email protected])