Block failure analysis using digital joint network …...4 Analytical Stereographic projection Key...
Transcript of Block failure analysis using digital joint network …...4 Analytical Stereographic projection Key...
Block failure analysis
using digital joint network
characterisation
A. Buyer & W. Schubert
Institute of Rock Mechanics and Tunnelling
Graz University of Technology
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Introduction
Discontinuity Controlled Block Failure
Description
Photo: SchubertPhoto: Schubert
„Rock is heavy and tends to fall down!“
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▪Mapping and description of the joint network geometry ▪ Conventional/manual▪ Digital
▪Definition of the rock mass geometry▪ Block size▪ Block shape▪ Block orientation
▪ Joint properties
▪Stress conditions
Introduction
Discontinuity Controlled Block Failure
Prediction
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▪Analytical▪ Stereographic projection
▪ Key Block Theory
▪Numerical▪ UDEC (2D) / 3DEC (3D)
▪ DDA
▪ UnWedge
▪ Etc.
Introduction
Discontinuity Controlled Block Failure
Analysis
Pötsch (2005)
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▪ Manual mapping of the joint network geometry is insufficient in:▪ Objectivity
▪ Statistical representivity
➢Rock mass models are:➢non-deterministic
➢unspecific
Improving the geotechnical design by applying digital rock mass characterization methods
Introduction
Academic Void and Objectives
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▪Vector-based joint plane detection (JPD)
▪Pixel-based joint trace detection (JTD)
➢Highliy detailed structure map of the joint network geometry
▪Direct implementation of the structure map into 3DEC ▪ Deterministic DFN approach
➢Explizit in joint position, orientation and size
Methodology
Assessment of the Joint Network Geometry
Mapping and modelling
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▪Discrete Element Modelling using 3DEC v.5.2 (Itasca CG, Inc.)
▪Deterministic DFN modelling
▪Actual tunnel specifications
▪Rigid body movement only
▪Sensitivity analysis regarding▪ Joint friction angles
▪ Circumferential stressconditions (K)
Methodology
Numerical Analysis
Model layout
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Case Study – Foliated rock mass
Joint Mapping
Combination of JTD and JPD
Set
ID
Dip Direction
[°]
Dip Angle
[°]
SA
[°]
Concentration DoO
[%]
CoC
[°]
NoM Colour
JS1 196 72 23.5 12.6 84.2 1.9 489 Green
JS2 325 5 18.5 19.9 90.0 1.2 703 Blue
JS3 059 77 21.8 14.5 86.2 1.8 467 Red
JS4 320 40 18.1 20.6 90.3 1.4 493 Yellow
JS5 114 85 27.8 9.2 78.3 2.6 361 Orange
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Case Study – Foliated rock mass
Numerical Analysis
Impressions
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Case Study – Foliated rock mass
Numerical Analysis
Sensitivity of j and K on SVB,0.01
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▪Good match between digital and manual joint mapping
▪Very good detection of the foliation by JTD (even internal folding)
▪Good detection of joint planes by JPD
▪Statistical assessment of the joint size distribution for the DFN worked well
Case Study – Foliated rock mass
Conclusion
Joint mapping
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▪Good match between actual and modelled excavation profile▪ Block detachments localized in correlation with geological documentation
▪ Detaching volumes rather low
▪Sensitivity analyses▪ High influence of j in case of block sliding (SSS-3)
▪ Increasing influence of K in case of confined blocks in the roof section (SSS-4)
Case Study – Foliated rock mass
Conclusion
Block stability analyses
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