Rock Mechanics/Seismology - Virginia Tech

Rock Mechanics/Seismology - Virginia Tech

Rock Mechanics/Geophysics Larry Costin, Sandia National Labs Paul Young, University of Toronto Discussion Points DUSEL Workshop November 12, 2004 We are here Path Forward Identify the big questions that can be addressed by DUSEL in a unique way Develop a roadmap for evolution of experiments & facilities Define infrastructure requirements Integrate with other groups to identify experiment sets with compatible infrastructure requirements Identify significant education outreach opportunities Motivation Significant trend toward greater utilization of underground space Critical infrastructure High hazard facilities Environmental protection Urban development Current engineering practice has heavy reliance on empirical design rules Influence of discontinuities Environmental factors Time-dependent behavior Lack of characterization methods for spatial variability Few opportunities for long-term R&D efforts

The Big Questions? Long-term degradation processes physical, chemical, coupled leading to weakening, rock fall, collapse over many years. Effect of spatial variability of rock mass properties on in situ stresses and stability of openings. Characterizing spatial variability. Validation of methods. Measurement of in situ stresses. TMHC(B) coupled processes and model validation. Validation of mechanics concepts DEM methods. Geophysical imaging and/or characterization of discontinuities and other features affecting rock mass behavior. Data fusion can we improve detection and characterization with data from multiple sensor types? Unique Opportunities? Ability to mine through ground truth validation of measurement and characterization methods. Long-term access for science. Ability to make measurements/observations over many years. Deep earth geophysics observatory. International collaboration. URL Experience Excavation scale testing for numerical model validation Mine-by Experiment Tunnel Sealing eXperiments to simulate radioactive waste repository conditions TSX Seismic methods used for remote detection and quantification of damage Monitoring and Modelling Results: URL Mine-by PFC simulation Excavatio n damage Potyondy and Cundall, 2001 Recorded seismicity PFC synthetic seismicity

48 days Hazzard et al, 2000 0 Moment magnitude -2.2 -3.7 URL Tunnel Sealing Experiment (TSX) Phases: Excavation (1997/98); Pressurisation (1999/02); Heating (2003); Cooling and Depressurisation (2004). Scale: Seal 20m x 4.4m x 3.5m URL TSX Induced Seismicity (1997 2003) Response to Excavation, Pressurization, and Heating A : Tunnel Excavation 95% of the events occur within 1.4m of the chamber wall. Events during heating do not extend further than during excavation Distance to Chamber Wall (m) 3 A B C D B : Bulkhead Key Excavation E F

C : Bulkhead Seal Construction 2 D : Chamber Fill and Pressurization to 2MPa 1 0 29/08/03 10/02/03 25/07/02 06/01/02 20/06/01 02/12/00 16/05/00 29/10/99 12/04/99 24/09/98 08/03/98 20/08/97 01/02/97 High rate of MS activity during excavation. Decay of MS events with pressurisation. Increase around chamber again, especially in the roof, during heating.

E : Chamber Pressurization to 4MPa F : Chamber Heating to 80C -120 -120 -140 -160 -140 -180 -200 -160 22/08/2003 -80 -100 23/05/2003 -80 21/02/2003 -20 22/11/2002 22/08/2003 23/05/2003 21/02/2003 22/11/2002 23/08/2002

24/05/2002 22/02/2002 23/11/2001 24/08/2001 40 Raypath P4_R8 20 0 1.5 0 -20 -40 -60 20 4.5 0 3.5 -20 2.5 -40 4.5 3.5 1.5 2.5 1.5 0.5 -100

-60 0.5 -0.5 -0.5 -1.5 -2.5 -1.5 -3.5 -2.5 -4.5 -3.5 Raypath P6_R13 -4.5 -200 -5.5 % Change in Youngs Modulus 60 % Change in Youngs Modulus Sand in Chamber 25/05/2001 23/02/2001 Clay Key Excavation 23/08/2002 -60

24/05/2002 22/08/2003 23/05/2003 20 22/02/2002 23/11/2001 21/02/2003 22/11/2002 24/11/2000 25/08/2000 26/05/2000 25/02/2000 26/11/1999 27/08/1999 Vs 24/08/2001 25/05/2001 23/08/2002 Water in Chamber 23/02/2001 24/05/2002 22/02/2002 23/11/2001 24/08/2001

25/05/2001 23/02/2001 24/11/2000 Clay Bulkhead Built 24/11/2000 25/08/2000 26/05/2000 25/02/2000 26/11/1999 28/05/1999 26/02/1999 27/11/1998 28/08/1998 29/05/1998 27/02/1998 28/11/1997 29/08/1997 E 25/08/2000 26/05/2000 25/02/2000 26/11/1999 27/08/1999

28/05/1999 26/02/1999 27/11/1998 28/08/1998 29/05/1998 30/05/1997 Vp 27/08/1999 28/05/1999 26/02/1999 27/11/1998 28/08/1998 29/05/1998 27/02/1998 -180 28/11/1997 P6 27/02/1998 R13 -40 28/11/1997 NE 0 29/08/1997 R8

30/05/1997 SW Velocity Change (m/s) P4 29/08/1997 NE Velocity Change (m/s) SW 30/05/1997 URL TSX Seismic Velocity Measurements 1997-2003: Temporal Changes to Rock Properties 4.5 3 -1.5 -5.5 Raypath P4_R8 Increase during excavation. Decrease during pressurization. Large increase during

heating. -3 Temperature Increase Pressure Increase Raypath P6_R13 Large decrease as clay key excavated and bulkhead built. Peaks due to evaporation experiment. Increase during heating. How do Earthquakes Scale? URL MS (Mw~-7 to -5) (Mw~-4 to -1) (from McGarr, 1999) Stress Drop URL AE Mw = -4 Moment Magnitude Mw = 8 Some questions left unanswered Can we use geophysical techniques to estimate permeability? How do we predict and validate the long term strength and behaviour of fractured rock? How do earthquake processes scale?

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