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Analytical solution of coupled stress-flow-transport processes in a single rock fracture
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
2011 (English)In: Computers & Geosciences, ISSN 0098-3004, E-ISSN 1873-7803, Vol. 37, no 9, 1437-1449 p.Article in journal (Refereed) Published
Abstract [en]

A closed-form solution is presented for modeling the coupled stress-flow-transport processes along a single fracture embedded in a porous rock matrix. Necessary assumptions were made to simplify the subject into a two-dimensional (2D) problem, considering the changes of fracture aperture and matrix porosity under various stress conditions. The cubic law was assumed to be valid for the fluid flow in the fracture, with an impermeable rock matrix. For transport mechanisms, advective transport along the fracture, longitudinal hydrodynamic dispersion in the flow direction, and the matrix diffusion were considered in three different transport models under constant concentration or constant flux (Danck- werts’) inlet boundary conditions. This analytical solution can be used as a constitutive model, or as an example for validation of similar constitutive models, for modeling the coupled hydro-mechanical- chemical (HMC) processes in fracture networks of crystalline rocks. The influences of stress/deformation processes on different transport mechanisms in a single fracture under different inlet boundary conditions were studied for the first time. The results show that changes of fracture, as controlled by a combination of normal closure and shear dilatancy, have a significant influence on the solute concentration distribution both along the fracture and in the rock matrix, as well as on the solute residence/breakthrough time, especially when shear-induced dilatancy occurs. Under compressions, the decreasing matrix porosity slightly increases the solute concentration along the fracture and in the rock matrix.

Place, publisher, year, edition, pages
2011. Vol. 37, no 9, 1437-1449 p.
Keyword [en]
Analytical solution, Fluid flow, Single rock fractures, Stress, Transport
National Category
Geotechnical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-42354DOI: 10.1016/j.cageo.2011.02.015ISI: 000295201500024Scopus ID: 2-s2.0-80051555169OAI: oai:DiVA.org:kth-42354DiVA: diva2:446867
Note
QC 20111010Available from: 2011-10-10 Created: 2011-10-10 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Stress Effects on Solute Transport in Fractured rocks
Open this publication in new window or tab >>Stress Effects on Solute Transport in Fractured rocks
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The effect of in-situ or redistributed stress on solute transport in fractured rocks is one of the major concerns for many subsurface engineering problems. However, it remains poorly understood due to the difficulties in experiments and numerical modeling. The main aim of this thesis is to systematically investigate the influences of stress on solute transport in fractured rocks, at scales of single fractures and fracture networks, respectively.

For a single fracture embedded in a porous rock matrix, a closed-form solution was derived for modeling the coupled stress-flow-transport processes without considering damage on the fracture surfaces. Afterwards, a retardation coefficient model was developed to consider the influences of damage of the fracture surfaces during shear processes on the solute sorption. Integrated with particle mechanics models, a numerical procedure was proposed to investigate the effects of gouge generation and microcrack development in the damaged zones of fracture on the solute retardation in single fractures. The results show that fracture aperture changes have a significant influence on the solute concentration distribution and residence time. Under compression, the decreasing matrix porosity can slightly increase the solute concentration. The shear process can increase the solute retardation coefficient by offering more sorption surfaces in the fracture due to gouge generation, microcracking and gouge crushing.

To study the stress effects on solute transport in fracture systems, a hybrid approach combing the discrete element method for stress-flow simulations and a particle tracking algorithm for solute transport was developed for two-dimensional irregular discrete fracture network models. Advection, hydrodynamic dispersion and matrix diffusion in single fractures were considered. The particle migration paths were tracked first by following the flowing fluid (advection), and then the hydrodynamic dispersion and matrix diffusion were considered using statistic methods. The numerical results show an important impact of stress on the solute transport, by changing the solute residence time, distribution and travel paths. The equivalent dispersion coefficient is scale dependent in an asymptotic or exponential form without stress applied or under isotropic compression conditions. Matrix diffusion plays a dominant role in solute transport when the hydraulic gradient is small.

Outstanding issues and main scientific achievements are also discussed.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. x, 108 p.
Series
Trita-LWR. PHD, ISSN 1650-8602
Keyword
Fractured rocks, Solute transport; Stress effects, Coupled stress-flow-transport processes; Analytical solution; Particle mechanics model; Fracture surface damage; Discrete element method; Particle tracking method
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-42361 (URN)978-91-7501-099-1 (ISBN)
Public defence
2011-11-04, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note
QC 20111011Available from: 2011-10-11 Created: 2011-10-10 Last updated: 2011-10-11Bibliographically approved

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