Antonio Bobet and Laura PyrakNolte

1
MECHANICAL AND GEOPHYSICAL CHARACTERIZATION OF
ROCK DAMAGE
Antonio Bobet and Laura Pyrak-Nolte Purdue
University
2
OUTLINE Objectives Motivation and
Background Experiments proposed Conclusions
3
Determine the fracturing mechanisms associated
with frictional fractures in brittle
materials Determine the seismic attributes
needs to characterize, geometrically and
mechanically, fracturing mechanisms Couple
mechanical response with geophysical
observations Evaluation of stiffness and
saturation of fracture from geophysical
measurements Upscale laboratory experiments to
DUSEL Evaluation of theoretical fracture
mechanics framework and geophysical theories
4
Laboratory Small - scale Tests Tensile Fracture
P- (square) and S-wave (circle) transmission
across tensile fracture
P-wave transmission
5
Laboratory Small - scale Tests Shear Fracture
S-wave transmission
6
Induce damage Changing stress field
through excavation - additional drifts may
be needed Unload pre-existing
discontinuities - shear zones Continuous
monitoring Geophysical sensors - seismic
wave transmission Other methods - AE
Couple mechanics of fracture and wave
transmission Upscale Fracture Mechanics and
Geophysical Theories
7
damage zone
Conceptual experiment setup
8

• CONCLUSIONS
• Damage assessment is important in rock
  mechanics
• Laboratory experiments show
• P- and S-wave transmission effective to detect
  damage
• possible to correlate mechanics with geophysics
• Large-scale tests needed DUSEL
• Experiments can be carried out at many scales
• Long-term experiments are possible
• Preliminary work needed
• stress field at DUSEL site, including pore
  pressures.
• rock mass properties and behavior at the test
  site.
• identification and characterization of
  suitable discontinuities.
• frictional strength and permeability of target
  discontinuities
• need additional laboratory work to couple
  mechanics-geophyisics