CIV1499HS, 2005
Material Fracture Dynamics: Experimental Methods
Lab Experiments
1. Elastic Wave Velocity Measurements (9h)
In this study, elastic wave velocities of several rocks are first measured as a function of
thermal treatment. Both P and S wave velocities will be measured in dry and wet conditions on
cubic samples along three different directions. The 5 rock samples of each rock will be thermally
treated at room temperature, 200oC, 400oC, 600oC, 800oC respectively. The rocks investigated
here are the following:
• Westerly granite sample, which is a well investigated granite, with coarse grain size
(150 µm) and very low initial anisotropy (<1%) as well. Initial P wave is equal to ~5.5km/s
while final should be lower than 3km/s due to quartz alpha-beta phase transition.
Cracking should be isotropic. Apart from the highly fractured specimen, effect of
saturation should be small.
• A canadian shield gneiss with coarse grain size (1mm). It is initially very anisotropic
(>20% presumably). Fast initial P wave is equal to 5.5km/s wile final should be lower than
3km/s due to quartz alpha-beta phase transition. Cracking should be anisotropic. Apart
from the highly fractured specimen, effect of saturation should be small.
• Carrara marble sample, which is a well investigated marble, with an initial coarse
grain size (150 µm) and low initial elastic anisotropy (<1%). Initial P wave was equal to
~5.6km/s while final P-wave should be lower than 3km/s. Final elastic anisotropy should
be negligible. Apart from the highly fractured specimen, effect of saturation should be
small.
• Fontainebleau sandstone is a coarse sandstone, with an initial porosity of ~10%, with
fine to medium grain size (0.1-1mm). It is initially almost isotropic and present a very high
permeability. Initial P wave is equal to 4km/s wile final should be lower than 3km/s due to
quartz alpha-beta phase transition. Cracking should be isotropic. Due to high porosity,
effect of saturation should be small.
The goal is to monitor the evolution of cracking, P wave anisotropy and shear wave
splitting as a function of thermal cracking and saturation. In the first lab, the students will learn
how to measure P and S wave velocities on 4 intact samples (one of each rock) using first
arrivals, double picking and/or cross-correlation techniques. In the second, they will measure the
P and S wave velocities (if possible, shear wave splitting as well) on 16 different samples in dry
conditions. In the third, they will measure P and S wave velocities on a few saturated samples (all
the sandstones, the most fractured specimens of granite, gneiss and marble).
They will have to produce a purely experimental report where they will have to show for
each rock:
• 1. the evolution of P and S wave velocities as a function of temperature treatment and
saturation.
• 2. The evolution of P wave anisotropy and amplitudes as a function of temperature
treatment and saturation.
• 3. The evolution of Shear wave splitting and S wave amplitudes as a function of
temperature treatment and saturation.
The data will be inverted and analyzed using Kachwin and other effective medium
theories and poro-elasticity later on during the program.
2. Brazilian Disk (9h)
Using Acoustic Emission (AE) techniques to study the evolution of failure processes
under Mode I fracture propagation using Cracked Chevron Notched Brazilian Disc (CCNBD). An
introduction to seismic theory will be given, with emphasis on techniques used in the InSite
software. This will include: (1) source location methods; (2) auto-picking techniques; (3)
frequency filtering; and (4) source mechanism calculation. The parameters from each technique
will be described as well as ways of optimizing the values for a particular experiment. This
session of the laboratory experiment consists of the following three subsections:
In the first lab, we monitor AE during Mode I fracture toughness test using the CCNBD
method. The rock sample is a Lac du Bonnet granite disc (diameter=20 cm, thickness=5.1cm)
which came from Canada's Underground Research Laboratory where the concept of deep
radioactive waste disposal is being studied. This CCNBD test is designed to measure the fracture
toughness at the tip of a "V"-shaped notch cut as well as the AE response to the nucleation and
propagation of tensile fracturing. An array of 20 transducers is used to give good 3D coverage of
the specimen. Using ESG Hyperion Giga Ram Recorder to monitor AE activity and ultrasonic
velocities, we will record during the test triggered and continuous full waveform data on 16
channels sampled at 10 MHz as the specimen is being loaded in a MTS servo control system at a
rate of 0.0005 mm/s.
In the second and third labs we will work with the AE data obtained form the similar
previous test. Detail of the steps includes:
• 1. Plotting of load and AE hits versus time for fracture initiation and dynamic failure.
• 2. Sensor location calibration using pulsing method and lead breaks to adopt the best
velocity structure for further analysis.
• 3. Hypocenter location and assessment of the evolution of fracture propagation with
time (pre-peak and post peak) using INSITE software.
• 4. Evaluation of fracture process zone properties using AE data.
• 5. Analysis of wave velocities surveys measured at different time across the fracture
plane before and after failure.
• 6. Focal mechanism analysis based on first motion polarity methods related to various
stage of loading, i.e. pre and post peak failure.
• 7. Event amplitude analysis related to pre and post peak periods.
The lab report would be prepared based on the objective of the test and analysis of the
data for the points outlined above.
3. A Concrete Structure Application (9h)
This part of the course will involve an experiment using AE and velocity measurements
on a concrete structure, a number of meters in size. The measurements will be used to image
and interpret the fractures induced in the structure as a result of changing load conditions.
Differences in the equipment used in this larger scale experiment, compared to the earlier smaller
scale experiments in rock, will be described. The software InSite will be used to process select
time periods of AE data (for source locations and magnitudes), as well as P-wave (and S-wave)
velocity change with time. Advanced interpretation methods will be applied to velocity raypaths
passing through regions where cracks are believed to be occurring. The software Kachwin will be
used to process the data to interpret microcrack parameters and orientations. The software will
also be applied to velocity results from measurements made in Part 1 of the course on cubic rock
specimens. Each student will be provided with the InSite and Kachwin software, as well as the
concrete data on CD. A report on the concrete experiment results will be produced, including a
section on the advance interpretation methods applied to fractured concrete and rock.