The Impact of Fracture Geometry on the Hydromechanical Behaviour of Crystalline Rock
Doktorsavhandling, 2015

Effective construction of tunnels in fractured crystalline rock requires a unified approach for handling rock mechanics and hydrogeological issues. Traditionally, rock mechanics and hydrogeology not only use different nomenclature, they also measure parameters such as e.g. aperture differently. A description of fractures that includes both fracture surface- and void geometry could be used as a basis for a conceptual model that allows complexity to be added to the descriptions of hydraulic and mechanical behaviour without contradictions. In this work, hydromechanically coupled experimental setups and methods were developed and used to improve a conceptual model of hydromechanical (HM) fracture behaviour at low compressive stress. Key aspects of the model are hydraulic aperture, fracture normal stiffness, the number of contacts between the surfaces, and the aspect ratio, i.e. the relationship between contact point distance and aperture, thus describing the voids between the surfaces. The experimental setups that were developed comprised equipment for in situ measurements of mechanical deformation due to stepwise hydraulic injection of fractures close to a tunnel, and a laboratory HM permeameter used in conjunction with fracture topography and aperture scanning. The latter produced high-resolution aperture maps of samples at 1.0 MPa, which were related to the flow rates, estimated hydraulic aperture and stiffness from the HM permeameter tests of the samples. Aiming at a common aperture-stiffness relationship for laboratory and in situ tests at different scales, the results were compared to a previously suggested relationship linking hydraulic aperture and normal stiffness. A relationship that has been devised from in situ hydraulic interference tests and is assumed to be valid for low comp-ressional stress across fractures with limited prior deformation. The few laboratory samples tested and the in situ tests performed show agreement with the aperture-stiffness relationship. A relationship and a conceptual model that have potential to provide support to future studies on hydromechanical behaviour of crystalline rock.

Laboratory experiments

Fracture aperture

In situ experiments

Conceptual model

Äspö HRL

Fracture geometry

Stereo photogrammetry

Hydromechanical coupling

Fracture normal stiffness

Hörsal VG, Sven Hultins Gata 6, Chalmers
Opponent: Dr. Thomas W. Doe, Golder Associates Inc. Redmond, Washington, USA

Författare

Johan Thörn

Chalmers, Bygg- och miljöteknik, Geologi och geoteknik

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Assigning Fracture Stiffness from In-Situ Deformation Measurements

1st International Discrete Fracture Network Engineering Conference, 20-22 oct 2014, Vancouver, Canada,; (2014)

Paper i proceeding

Hydromechanical characterization of fractures close to a tunnel opening: A case study

ISRM International Symposium - EUROCK 2012,; (2012)

Paper i proceeding

A new apparatus and methodology for hydromechanical testing and geometry scanning of a rock fracture under low normal stress

International Journal of Rock Mechanics and Minings Sciences,; Vol. 79(2015)p. 216-226

Artikel i vetenskaplig tidskrift

Hydraulic and Hydromechanical Laboratory Testing of Large Crystalline Rock Cores

Rock Mechanics and Rock Engineering,; Vol. 48(2015)p. 61-73

Artikel i vetenskaplig tidskrift

Styrkeområden

Building Futures (2010-2018)

Ämneskategorier

Samhällsbyggnadsteknik

Geologi

ISBN

978-91-7597-274-9

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 3955

Hörsal VG, Sven Hultins Gata 6, Chalmers

Opponent: Dr. Thomas W. Doe, Golder Associates Inc. Redmond, Washington, USA

Mer information

Skapat

2017-10-07