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Anisotropy of strength and deformability of fractured rocks
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
2014 (English)In: Journal of Rock Mechanics and Geotechnical Engineering, ISSN 1674-7755, Vol. 6, no 1, 156-164 p.Article in journal (Refereed) Published
Abstract [en]

Anisotropy of the strength and deformation behaviors of fractured rock masses is a crucial issue fordesign and stability assessments of rock engineering structures, due mainly to the non-uniform and nonregulargeometries of the fracture systems. However, no adequate efforts have been made to study thisissue due to the current practical impossibility of laboratory tests with samples of large volumes containingmany fractures, and the difficulty for controlling reliable initial and boundary conditions forlarge-scale in situ tests. Therefore, a reliable numerical predicting approach for evaluating anisotropy offractured rock masses is needed. The objective of this study is to systematically investigate anisotropy ofstrength and deformability of fractured rocks, which has not been conducted in the past, using a numericalmodeling method. A series of realistic two-dimensional (2D) discrete fracture network (DFN)models were established based on site investigation data, which were then loaded in different directions,using the code UDEC of discrete element method (DEM), with changing confining pressures. Numericalresults show that strength envelopes and elastic deformability parameters of tested numerical modelsare significantly anisotropic, and vary with changing axial loading and confining pressures. The resultsindicate that for design and safety assessments of rock engineering projects, the directional variations ofstrength and deformability of the fractured rock mass concerned must be treated properly with respectto the directions of in situ stresses. Traditional practice for simply positioning axial orientation of tunnelsin association with principal stress directions only may not be adequate for safety requirements.Outstanding issues of the present study and suggestions for future study are also presented.

Place, publisher, year, edition, pages
2014. Vol. 6, no 1, 156-164 p.
Keyword [en]
Anisotropy, Strength criterion, Deformation behavior, Numerical experiments, Fractured rock mass, Discrete element method (DEM), Discrete fracture network (DFN)
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-155712DOI: 10.1016/j.jrmge.2014.01.009Scopus ID: 2-s2.0-84925287460OAI: oai:DiVA.org:kth-155712DiVA: diva2:762153
Note

QC 20141111

Available from: 2014-11-10 Created: 2014-11-10 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Strength and deformability of fractured rocks
Open this publication in new window or tab >>Strength and deformability of fractured rocks
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents a systematic numerical modeling framework to simulate the stress-deformation and coupled stress-deformation-flow processes by performing uniaxial and biaxial compressive tests on fractured rock models with considering the effects of different loading conditions, different loading directions (anisotropy), and coupled hydro-mechanical processes for evaluating strength and deformability behavior of fractured rocks. By using code UDEC of discrete element method (DEM), a series of numerical experiments were conducted on discrete fracture network models (DFN) at an established representative elementary volume (REV), based on realistic geometrical and mechanical data of fracture systems from field mapping at Sellafield, UK. The results were used to estimate the equivalent Young’s modulus and Poisson’s ratio and to fit the Mohr-Coulomb and Hoek-Brown failure criteria, represented by equivalent material properties defining these two criteria.

The results demonstrate that strength and deformation parameters of fractured rocks are dependent on confining pressures, loading directions, water pressure, and mechanical and hydraulic boundary conditions. Fractured rocks behave nonlinearly, represented by their elasto-plastic behavior with a strain hardening trend. Fluid flow analysis in fractured rocks under hydro-mechanical loading conditions show an important impact of water pressure on the strength and deformability parameters of fractured rocks, due to the effective stress phenomenon, but the values of stress and strength reduction may or may not equal to the magnitude of water pressure, due to the influence of fracture system complexity. Stochastic analysis indicates that the strength and deformation properties of fractured rocks have ranges of values instead of fixed values, hence such analyses should be considered especially in cases where there is significant scatter in the rock and fracture parameters. These scientific achievements can improve our understanding of fractured rocks’ hydro-mechanical behavior and are useful for the design of large-scale in-situ experiments with large volumes of fractured rocks, considering coupled stress-deformation-flow processes in engineering practice. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. xvi, 97 p.
Series
TRITA-LWR. PHD, ISSN 1650-8602 ; 2014:07
Keyword
Fractured crystalline rocks, Numerical experiments, Discrete element methods (DEM), Discrete fracture network (DFN), Representative elementary volume (REV), Coupled hydro-mechanical processes, Anisotropy, Effective stress, Failure criteria, Stochastic realizations
National Category
Engineering and Technology
Research subject
Land and Water Resources Engineering
Identifiers
urn:nbn:se:kth:diva-155719 (URN)978-91-7595-324-3 (ISBN)
Public defence
2014-11-25, F3, Lindstedsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20141111

Available from: 2014-11-11 Created: 2014-11-10 Last updated: 2014-11-11Bibliographically approved

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