Rock Mechanics/Geophysics Larry Costin, Sandia National Labs Paul Young, University of Toronto Discussion Points November 12, 2004 DUSEL Workshop

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 We are here

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 Moment magnitude PFC synthetic seismicity 0 48 days Potyondy and Cundall, Recorded seismicity PFC simulation Excavation damage Hazzard et al, 2000

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 High rate of MS activity during excavation. Decay of MS events with pressurisation. Increase around chamber again, especially in the roof, during heating. A : Tunnel Excavation B : Bulkhead Key Excavation C : Bulkhead Seal Construction D : Chamber Fill and Pressurization to 2MPa E : Chamber Pressurization to 4MPa F : Chamber Heating to 80°C 95% of the events occur within 1.4m of the chamber wall. Events during heating do not extend further than during excavation

URL TSX Seismic Velocity Measurements : Temporal Changes to Rock Properties Raypath P6_R13 Large decrease as clay key excavated and bulkhead built. Peaks due to evaporation experiment. Increase during heating. Raypath P4_R8 Increase during excavation. Decrease during pressurization. Large increase during heating. SW NE P4 R8 SW NE R13 P6

How do Earthquakes Scale? M w = -4 M w = 8 URL AE (M w ~-7 to -5) URL MS (M w ~-4 to -1) (from McGarr, 1999) Stress Drop Moment Magnitude

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?