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Stochastic analysis of strength and deformability of fracture rocks using multi-fracture system realizations
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.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In this paper, a systematic numerical framework is presented to predict stochastic variationsof strength and deformation parameters of fracture rocks, using multiple realizations ofstochastic discrete fracture network (DFN) models at established representative elementaryvolume (REV). Fifty 2D square geometrical models, which are generated using the MonteCarlo technique of the fracture system based on the data obtained from a real site, aregenerated for stochastic analysis of results of stress-deformation behaviors from a series of350 compressive numerical experiments, using the discrete element method (DEM). The Chi-Squared goodness-of-fit test was used to frequency and probability and cumulativedistribution functions (PDF-CDF) of the strength and deformability of fracture rocksdistributions. The results show that (i) the Young’s modulus and Poisson’s ratio during elasticdeformation stages have normal and lognormal distributions, respectively, (ii) both thefriction angle and cohesion derived from Mohr-Coulomb (M-C) strength criterion obeynormal distributions, (iii) the m and s parameters of Hoek-Brown (H-B) strength criterionhave lognormal distributions. The results of stochastic analysis show that it is a usefultechnique for evaluating random variations of strength and deformability parameters of thefractured rock, in cases where there is significant scatter in the rock and fracture parameters.

Keywords [en]
Discrete Element Methods (DEM-DFN), Stress-Deformation Analysis, UDEC, Failure Criteria, Numerical Experiment, Stochastic Realization
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-155716OAI: oai:DiVA.org:kth-155716DiVA, id: diva2:762159
Note

QS 2014

Available from: 2014-11-10 Created: 2014-11-10 Last updated: 2014-11-11Bibliographically 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. p. xvi, 97
Series
TRITA-LWR. PHD, ISSN 1650-8602 ; 2014:07
Keywords
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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