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Water pressure effects on strength and deformability of fractured rocks under low confining pressures
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.
2015 (English)In: Journal of Rock Mechanics and Geotechnical Engineering, ISSN 1674-7755, Vol. 48, no 3, 971-985 p.Article in journal (Refereed) Published
Abstract [en]

The effect of groundwater on strength anddeformation behavior of fractured crystalline rocks is one ofthe important issues for design, performance and safetyassessments of surface and subsurface rock engineeringproblems. However, practical difficulties make the directin situ and laboratory measurements of these properties offractured rocks impossible at present, since effects of complexfracture system hidden inside the rock masses cannot beaccurately estimated. Therefore, numerical modeling needs tobe applied. The overall objective of this paper is to deepenour understanding on the validity of the effective stressconcept, and to evaluate the effects of water pressure onstrength and deformation parameters. The approach adopteduses discrete element methods to simulate the coupled stressdeformation-flow processes in a fractured rock mass withmodel dimensions at a representative elementary volume(REV) size and realistic representation of fracture systemgeometry. The obtained numerical results demonstrate thatwater pressure has significant influence on the strength, butwith minor effects on elastic deformation parameters, comparedwith significant influence by the lateral confiningpressure. Also, the classical effective stress concept to fracturedrock can be quite different with that applied in soilmechanics. Therefore, one should be cautious when applyingthe classical effective stress concept to fractured rock media.

Place, publisher, year, edition, pages
2015. Vol. 48, no 3, 971-985 p.
Keyword [en]
Coupled hydro-mechanical, Effective stress, Discrete element methods (DEM-DFN), UDEC, Failure criteria, Fractured crystalline rocks
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-155713DOI: 10.1007/s00603-014-0628-3ISI: 000352905100006Scopus ID: 2-s2.0-84928376984OAI: oai:DiVA.org:kth-155713DiVA: diva2:762155
Note

Updated from E-publ to published. QC 20150630

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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