Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Scale and Stress Effects on Hydro-Mechanical Properties of Fractured Rock Masses
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

In this thesis, the effects of size and stress on permeability, deformability and strength of fractured rock masses are investigated. A comparison study was carried out to examine the effects of considering, or not considering, the correlation between distributions of fracture apertures and fracture trace lengths on the hydro-mechanical behavior of fractured rocks. The basic concepts used are the fundamental principles of the general theory of elasticity, Representative Elementary Volume (REV), the tensor of equivalent permeability, and the strength criteria of the fractured rocks.

Due to the size and stress dependence of the hydro-mechanical properties of rock fractures, the overall effective (or equivalent) hydro-mechanical properties of the fractured rocks are also size and stress-dependent. However, such dependence cannot be readily investigated in laboratory using small samples, and so numerical modeling becomes a necessary tool for estimating their impacts. In this study, a closed-form relation is established for representing the correlation between a truncated lognormal distribution of fracture apertures and a truncated power law distribution of trace lengths, as obtained from field mapping. Furthermore, a new nonlinear algorithm is developed for predicting the relationship between normal stress and normal displacement of fractures, based on the Bandis model and the correlation between aperture and length.

A large number of stochastic Discrete Fracture Network (DFN) models of varying sizes were extracted from some generated large-sized parent realizations based on a realistic fracture system description from a site investigation programme at Sellafield, UK, for calculating the REV of hydro-mechanical properties of fractured rocks. Rotated DFN models were also generated and used for evaluation of the distributions of directional permeabilities, such that tensors of equivalent permeability could be established based on stochastically established REVs. The stress-dependence of the permeability and the stress-displacement behaviour were then investigated using models of REV sizes. The Discrete Element Method (DEM) was used for numerical simulation of the fluid flow, deformability properties and mechanical strength behavior of fractured rocks.

The results show significant scale-dependency of rock permeability, deformability and strength, and its variation when the correlation between aperture and trace length of fractures are concerned, with the overall permeability and deformability more controlled by dominating fractures with larger apertures and higher transmissivity and deformability, compared with fracture network models having uniform aperture. As the second moment of aperture distribution increases, a fractured rock mass shows more discrete behavior and an REV is established in smaller value of second moment with much larger model size, compared with the models with uniform fracture aperture. When the fracture aperture pattern is more scattered, the overall permeability, Young’s modulus and mechanical strength change significantly.

The effect of stress on permeability and fluid flow patterns in fractured rock is significant and can lead to the existence or non-existence of a permeability tensor. Stress changes the fluid flow patterns and can cause significant channeling and the permeability tensor, and REV may be destroyed or re-established at different applied stress conditions. With an increase in the confining stress on the DEM models, the strength is increased. Compared with the Hoek-Brown criterion, the Mohr-Coulomb strength envelope provides a better fit to the results of numerical biaxial compression tests, with significant changes of the strength characteristic parameters occurring when the second moment of the aperture distribution is increased.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , xiv, 76 p.
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1040
Keyword [en]
Aperture-trace length correlation; Discrete Fracture Network (DFN); Representative Elementary Volume (REV); Strength; Stress-Strain curve; Discrete Element Method (DEM); Stress effect; Deformability of fractures
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:kth:diva-4772ISBN: 978-91-7415-003-2 (print)OAI: oai:DiVA.org:kth-4772DiVA: diva2:13871
Public defence
2008-06-04, V3, Mark och Vatenteknik, Teknikringen 72, Mark och Vatenteknik, 10:00
Opponent
Supervisors
Note
QC 20100702Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2010-07-02Bibliographically approved
List of papers
1. Hydraulic properties of fractured rock masses with correlated fracture length and aperture
Open this publication in new window or tab >>Hydraulic properties of fractured rock masses with correlated fracture length and aperture
2007 (English)In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 44, no 5, 704-719 p.Article in journal (Refereed) Published
Abstract [en]

Permeability of fractured rocks is investigated considering the correlation between distributed fracture aperture and trace length, based on a newly developed correlation equation. The influence of the second moment of the lognormal distribution of apertures on the existence of representative elementary volume (REV), and the possibility of equivalent permeability tensor of the fractured rock mass, is examined by simulating flow through a large number of stochastic discrete fracture network (DFN) models of varying sizes and varying fracture properties.

The REV size of the DFN models increases with the increase of the second moment of the lognormal distribution, for both the correlated and uncorrelated cases. The variation of overall permeability between different stochastic realizations is an order of magnitude larger when the aperture and length are correlated than when they are uncorrelated. The mean square error of the directional permeability increases with increasing value of the second moment of the lognormal distribution function, and good fitting to an ellipsis of permeability tensor can only be reached with very large sizes of DFN models, compared with the case of constant fracture aperture, regardless of fracture trace length.

Keyword
aperture distribution; correlation permeability; fracture rocks; representative elementary volume (REV); discrete fracture network (DFN); CRYSTALLINE ROCK; FIELD DATA; NETWORKS; FLOW; DISTRIBUTIONS; CONNECTIVITY; PERMEABILITY; MEDIA; MODEL; TRANSMISSIVITY
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-8519 (URN)10.1016/j.ijrmms.2006.11.001 (DOI)000245872400004 ()2-s2.0-33847284549 (Scopus ID)
Note
QC 20100701Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2017-12-14Bibliographically approved
2. Stress effects on permeability in fractured rock mass with correlated fracture length and aperture
Open this publication in new window or tab >>Stress effects on permeability in fractured rock mass with correlated fracture length and aperture
2008 (English)In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 45, no 8, 1320-1334 p.Article in journal (Refereed) Published
Abstract [en]

The effect of stress on permeability and fluid flow patterns in fractured rock masses is studied when distributed fracture aperture is correlated with fracture trace length, using a discrete element method (DEM). The basic assumptions are that the rock matrix is impermeable and linearly elastic, and that the fluid flows only in fractures. A new nonlinear algorithm is developed for prediction of normal stress-normal displacement behavior of fractures based on the Bandis model and the correlation between aperture and length. The results show that when small stress ratios (K = horizontal/vertical stress) are applied at the model boundaries, the overall permeability of the fracture network is generally decreased. However, contribution from a few large fractures of higher hydraulic conductivity prevents drastic reduction of the overall permeability, compared with models that assume uniform fracture apertures. With large values of the stress ratio, both the overall permeability and flow patterns are controlled by a combination of highly conductive larger fractures and fractures with shear slipping and dilation, with much increased overall permeability and shear-induced flow channeling. With increasing stress ratios, it becomes more and more difficult to establish an equivalent permeability tensor and representative elementary volume (REV) of a fractured rock, compared with the unstressed model. These results show significant difference between correlated and non-correlated aperture and fracture length distributions, and highlight more significant scale and stress dependence of hydro-mechanical behavior of fractures rocks when geometric parameters of rock fractures are correlated.

Keyword
Stress effect; Scale effect; Equivalent permeability tensor; Aperture-trace length correlation; Fracture rocks; Discrete fracture network; Deformability of fractures; Discrete element method; HYDRAULIC-PROPERTIES; FLUID-FLOW; FIELD DATA; NETWORKS; TENSOR; MODEL; DEFORMATION; STIFFNESS; JOINT; CALIBRATION
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-8520 (URN)10.1016/j.ijrmms.2008.01.015 (DOI)000260926500009 ()2-s2.0-55749098480 (Scopus ID)
Note
QC 20100701Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2017-12-14Bibliographically approved
3. Stress and scale effects of the hydraulic properties of fractured rocks
Open this publication in new window or tab >>Stress and scale effects of the hydraulic properties of fractured rocks
2008 (English)In: Boundaries of rock mechanics: recent advances and challenges for the 21st century : proceedings of the International Young Scholars' Symposium on Rock Mechanics, 28 April-2 May, 2008, Beijing, China / [ed] Meifeng Cai, Jin'an Wang, 2008, 41-48 p.Conference paper, Published paper (Refereed)
Abstract [en]

The paper investigates the stress and scale effects on the hydraulic permeability of fractured rocks considering the correlation between distributed fracture aperture and trace length, where the fracture aperture and trace length follow a truncated lognormal distribution and a power-law distribution, respectively This parameter correlation of fractures leads to larger REV size and permeability magnitudes of the DEM models compared with the case of using constant apertures, which vary with stress conditions, and with the overall permeability more controlled by large-sized fractures.

Series
Proceedings and Monographs in Engineering, Water and Earth Sciences
Keyword
LENGTH; APERTURE; MASSES; PERMEABILITY
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-8522 (URN)10.1201/9780203883204.pt2 (DOI)000256216600009 ()2-s2.0-56449083705 (Scopus ID)978-0-415-46934-0 (ISBN)
Conference
International Young Scholars' Symposium on Rock Mechanics, Beijing, PEOPLES R CHINA, APR 28-MAY 02, 2008
Note
QC 20100702. Uppdaterad från manuskript till konferensbidrag (20100702). Tidigare titel: Stress and scale-dependency of the hydraulic properties of fractured rocks.Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2010-07-06Bibliographically approved
4. Scale and stress effects on permeability tensor of fractured rocks with correlated fracture length and aperture
Open this publication in new window or tab >>Scale and stress effects on permeability tensor of fractured rocks with correlated fracture length and aperture
2008 (English)In: Thermo-Hydromechanical and chemical coupling in geomaterials and applications: Proceedings of the 3rd International Symposium GeoProc’2008 / [ed] Nicolas Burlion, Jian-Fu Shao, 2008, 439-446 p.Conference paper, Published paper (Refereed)
Abstract [en]

The effect of stress on permeability tensor and Representative Elementary Voliume (REV) of fractured rock masses is studied using a Discrete Element Approach (DEM). A new nonlinear model of rock fractures is developed for prediction of normal stress-normal displacement behavior of fractures based on the correlation between fracture aperture and length distributions. The results show that at small differential stress ratios K (=horizontal/vertical stresses) the overall permeability of fracture networks is generally decreased. However contribution from a few large fractures of higher hydraulic conductivity prevents drastic reduction of the overall permeability, compare with DFN models of constant fracture apertures regardless of fracture trace length. With large values of differential stress ratios, the overall permeability of the DFN models is controlled by a combination of highly conductive larger fractures and fractures with shear slipping and dilation. With increasing differential stress ratios (K=1,3,4 and 5) the REV of a fractured rock may exist at much larger model sizes comparing with the model without stress (K=0).

National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-8523 (URN)978-1-84821-043-1 (ISBN)
Conference
3rd International Symposium GeoProc’2008, Lille, France
Note
QC 20100702. Uppdaterad från manuskript till konferensbidrag (20100702).Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2010-07-06Bibliographically approved
5. Effects of size and stress on deformability and strength of fractured rocks with correlated fracture aperture and length
Open this publication in new window or tab >>Effects of size and stress on deformability and strength of fractured rocks with correlated fracture aperture and length
2008 (English)In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545Article in journal (Other academic) Submitted
Keyword
Aperture; Correlation; Strength; Stress-Strain curve; Representative Elementary Volume (REV); Discrete Fracture Network (DFN); Discrete Element Method (DEM)
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-8521 (URN)
Note
QS 20120314Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2017-12-14Bibliographically approved

Open Access in DiVA

fulltext(2276 kB)1710 downloads
File information
File name FULLTEXT01.pdfFile size 2276 kBChecksum MD5
6d0b6ef9d58d54b0ada7ee652910b66f8abc5ea327c3610ecad0542301f0fefbbe047c62
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Baghbanan, Alireza
By organisation
Engineering Geology and Geophysics
Earth and Related Environmental Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 1710 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 1155 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf