A Large Block Test to Study the Energetic Failure of Rock – Application to Rock-Bursting and Earthquake Mechanics Maochen Ge, Eliza Richardson, Chris Marone, Derek Elsworth, EMS, PSU & Erik Westman, VPI

Objectives Develop an improved understanding of the deformation and energetic failure of rock masses –Contribute to the safe design of structures (e.g. infrastructure and caverns) –Improved understanding of rock failure in space and time –Address a “big” question: Rupture mechanics and AE/MS/RB/Equake scaling

Slide-Hold-Slide Friction Experiments Hold periods of 30 – 10 4 [sec]Hold periods of 30 – 10 4 degree-C, peak coefficient is independent of hold degree-C, peak value increases with increase of hold

Slide-Hold-Slide Friction Experiments Frictional strengthening is likely due to augmentation in cohesion (contact area) that may result from pressure solution

Scale Effects in Geo-hydrology – Space and Time Spatial Scale, m Permeability, m Lab scaleField scale Regional scale ?

Constitutive Relations for Transport Behavior

Approach The Challenge – –Understanding rock-bursting and minimizing impact The Opportunities – –Understanding failure processes at field scale and linking failure with source mechanisms –Understanding fundamental rate and state constitutive laws – and scale-up: In space In time

Five months of seismicity at Mponeng Over 80,000 events Colors grade from cool to warm as events become more recent

Creighton Mine, Canada

Approach The Challenge – –Understanding rock-bursting and minimizing impact The Opportunities – –Understanding failure processes at field scale and linking failure with source mechanisms and event scaling –Understanding fundamental rate and state constitutive laws – and scale-up: In space In time

Multiple pillars (of differing dimension) constructed at multiple depths; may include discontinuities Experimental Arrangement

Environmental Loads Excavation Excess fluid pressures Monitoring Scales Run of facility Cavern Test Monitoring and Testing Imaging – seismics & ERT – rupture types, sizes and locations Solid – stress, strain, extension, 4-D seismics, tilt Fluid – liquid and gas - pressure and composition – permeability and reactive chemistry Fluid pressure Flow and reaction

How does this experiment optimize the use of DUSEL? Time, t Spatial scale, x,y,z Depth, z ->  Principal Attributes 1.Unusual spatial scale – bridges laboratory scale to field scale 2.Long-term access 3.Depth gives stress and thermal regimes……

Important Questions Mechanisms of the triggering of rupture Mechanisms of strength-gain and fault-healing –Role of reactive fluids –Role of pressure solution and other mechanisms Understanding the transition - quiescent rupture and energetic failure. Bridging the gap between laboratory and field scales Illuminating fundamental mechanics of Rate and State friction constitutive laws –Representation of seismic and interseismic fault behaviors –Earthquake nucleation, coseismic rupture and earthquake afterslip Role of fault roughness and gouge on frictional properties and stability ………………….

Expected Results Address Issues Relating to: Stability of large openings against energetic failure Improved understanding of the energetic failure of rock –Small scale for civil and mined underground structures –Large scale (space and time) for earthquake mechanics

Experimental Requirements Contained and remote – possibly part of a “Large Experiment” Facility Duration – Long term experiment (10y) on large volume natural fault/fracture. Subsidiary short-term expts (~1,s to ~10,s of meters edge-dimension) for short term on block periphery Reusability – Not likely for small experiments, possible for large block. No compatibility with physics experimentation – except monitoring of cavern excavation sequence Needs appropriate fault/stress/strength structure